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Nonmedical use of prescription stimulants in the United States
Drug and Alcohol Dependence 84 (2006) 135–143
Nonmedical use of prescription stimulants in the United States夽 Larry A. Kroutil a,∗ , David L. Van Brunt b , Mindy A. Herman-Stahl a , David C. Heller a , Robert M. Bray a , Michael A. Penne a b
a RTI International, 3040 Cornwallis Road, Research Triangle Park, NC 27709, USA Lilly Research Laboratories, Lilly Corporate Center, DC0825, Indianapolis, IN 46285, USA
Received 17 June 2005; received in revised form 17 December 2005; accepted 21 December 2005
Abstract Objective: This study estimated prevalences and correlates of stimulant diversion in the United States and examined relationships between diversion and measures of abuse or dependence. Methods: We conducted descriptive and multivariate analysis of data from the National Survey on Drug Use and Health. Key measures were nonmedical use (misuse) of any prescription stimulant, any stimulant other than methamphetamine, and stimulants indicated for attentiondeficit/hyperactivity disorder (ADHD). Results: Lifetime stimulant misuse included some misuse of longer-acting ADHD drugs. The majority of past-year misuse involved drugs other than methamphetamine, particularly for youth aged 12–17. Past year misuse was more prevalent among persons aged 12–25, compared with older adults, and among Whites, compared with other groups. Prevalences in large metropolitan areas were lower than or similar to those in less populated areas. About 13% of past-year stimulant misusers met the survey criteria for dependence or abuse, as did about 10% of persons aged 12–25 who misused only nonmethamphetamine stimulants. Conclusions: Most stimulant misuse in the United States (particularly among youth) involved prescription drugs other than methamphetamine. The problem is not limited to metropolitan areas. © 2006 Elsevier Ireland Ltd. All rights reserved. Keywords: Attention-deficit/hyperactivity disorder (ADHD); Stimulants; Methamphetamine; Nonmedical use; Correlates
1. Introduction Stimulants are prescribed for effective treatment of a variety of medical conditions, including narcolepsy, attentiondeficit/hyperactivity disorder (ADHD), and obesity. Despite the therapeutic value of these medications, concerns have arisen about their diversion for nonmedical use (i.e., misuse). In 1998, 夽 Findings that were recently released from the 2004 NSDUH, subsequent to the initial preparation of this manuscript, indicated that the prevalences of past-year misuse of any stimulant and of methamphetamine have been stable from 2002 through 2004 for persons aged 12 years or older and among adult age groups. Among youths aged 12–17 years, however, the past-year prevalence of any stimulant misuse in 2004 (2.0%) was found to be significantly lower than the prevalence in 2002 (P < 0.01); the prevalence in 2003 and 2004 was stable [see SAMHSA, 2005. Results from the 2004 National Survey on Drug Use and Health: National Findings. Author, Rockville, MD (Office of Applied Studies, NSDUH Series H-28, DHHS Publication No. SMA 05-4062)]. ∗ Corresponding author. Tel.: +1 919 541 6067; fax: +1 919 485 5555. E-mail address: [email protected] (L.A. Kroutil).
0376-8716/$ – see front matter © 2006 Elsevier Ireland Ltd. All rights reserved. doi:10.1016/j.drugalcdep.2005.12.011
Goldman et al. conducted a review on ADHD, motivated in part by public concern surrounding the increase in production and use of methylphenidate (Ritalin) and resulting questions about the prevalence of diversion. This study concluded that stimulant misuse and diversion were not a major problem at the time but speculated that trends toward expanding production could increase diversion in the future. According to the Drug Enforcement Administration, the methylphenidate production quota (i.e., the amount approved for manufacturing) increased from 1768 kg in 1990 to 14,957 kg in 2000 (Woodworth, 2000). Concomitantly, the number of adolescents and adults being treated for ADHD with prescription stimulants has risen steadily since 1990 (Goldman et al., 1998; Robison et al., 1999). In a recent survey of physicians, 19% reported concern over stimulant diversion for nonmedical use, notwithstanding the established efficacy of stimulants for the treatment of ADHD (Stockl et al., 2003). Concern over the misuse of these medications has garnered popular media attention as well (Zamiska, 2004; Degrandpre, 2000).
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Public health concern is warranted, as both treatment admissions and law enforcement data suggest that problems relating to nonmedical stimulant use are increasing (Drug and Alcohol Services Information System, 2004; Strom et al., 2004). Further, the side effects of legitimate medical use of ADHD stimulants can be sufficiently serious to warrant immediate discontinuation (Barkley et al., 1990). In early 2005, the U.S. Food and Drug Administration (FDA, 2005a) issued a public health advisory for two amphetamine products used to treat ADHD, Adderall® and Adderall XR® , due to reports of sudden, unexplained deaths of pediatric patients taking these medications. In June 2005, the Pediatric Advisory Committee to the FDA (2005b) reported concerns about potential adverse psychiatric or cardiovascular events associated with methylphenidate products; the FDA indicated plans to make labeling changes to describe these events. Given the potential for serious side effects among patients taking these medications under medical supervision, there is even more reason for concern about adverse physical or psychiatric problems associated with use of these medications outside of any such supervision. Recent data from the National Survey on Drug Use and Health (NSDUH, formerly the National Household Survey on Drug Abuse [NHSDA]) indicate that an estimated 21 million persons aged 12 or older in the United States, or about 9%, have used prescription stimulants nonmedically at some point in their lifetimes. This estimate includes an estimated 12 million persons reporting nonmedical use of methamphetamine, which is often produced illegally. In both 2002 and 2003, however, more than half of the target population who used stimulants nonmedically in the past year reported using stimulants other than methamphetamine (Substance Abuse and Mental Health Services Administration [SAMHSA], 2004a). Despite evidence of nonmedical stimulant use by a substantial number of persons, little is known about the types of stimulants that are misused, the characteristics of these users, and associated problems. Although the published reports of findings from NSDUH cover a broad spectrum of substances, these reports present no more than limited descriptive information on misuse of any prescription stimulants relative to misuse of methamphetamine. Further, these reports do not provide informative demographic breakdowns that distinguish prescription stimulants as a group from street drugs. Nor do these standard reports offer covariate-adjusted comparisons of these prevalences. Therefore, the present study addresses gaps in knowledge about prescription stimulant misuse by analyzing NSDUH data in greater detail. We focus on non-methamphetamine and ADHD-specific drugs. The study objectives were to identify (a) important demographic and geographic correlates of nonmedical stimulant use for users of different subtypes of stimulants, (b) correlates of nonmedical use when potential confounding factors are taken into account, and (c) relationships linking different subtypes of nonmedical stimulant use with survey-based syndromes of Diagnostic and Statistical Manual of Mental Disorders (DSM-IV) drug dependence or abuse (American Psychiatric Association, 1994).
2. Methods 2.1. Data sources We used the public use file from the 2002 NSDUH, an annual survey of the civilian, noninstitutionalized population aged 12 or older in the United States (excluding homeless people not living in shelters), as our principal data source (SAMHSA, 2003). We used the combined 2000 and 2001 NSDUH public use files for analyses of substance dependence or abuse because the 2002 file did not contain adequate numbers of respondents for reliable estimation of the prevalence of dependence or abuse clinical features among important subgroups of stimulant misusers. All data files were converted into SAS Version 8 data files for analysis. NSDUH uses a multistage, probability sampling design. Selection of dwelling units in all 50 states and the District of Columbia is followed by inperson screening of sampled dwelling units to identify eligible members aged 12 or older, then random selection of eligible household residents for interview. Interviews are conducted over the course of the year. Respondents in 2002 were given a US$30 gratuity for participation. NSDUH respondents are typically interviewed in their homes. Questions about drug use (including nonmedical stimulant use) and other sensitive behaviors are self-administered using audio computer-assisted self-interviewing. The computer-assisted design reduces opportunities for inconsistent answers by skipping respondents out of questions that do not apply, based on respondents’ prior answers. The occurrence of inconsistent data is further reduced through the use of consistency checks built into the questionnaire program for key items. These consistency checks alert respondents when they have entered an answer that is inconsistent with a previous answer (e.g., misuse of methamphetamine in a more recent period than the most recent period reported for misuse of any stimulant), thereby providing respondents with an opportunity to resolve inconsistencies while the interview is in progress (Kroutil and Handley, 2004). These interview design features do not eliminate missing data, however, because respondents can indicate that they do not know an answer or can refuse to answer. Further, the consistency checks mentioned above do not cover every possible inconsistency in the drug use questions. Therefore, when drug use data are missing or ambiguous, statistical imputation procedures are used to classify respondents as users or nonusers or to assign a definite period when they last used a given drug. The 2002 NSDUH had a weighted screening response rate of 91% and a weighted interview response rate of 79%. Data from a total final sample of 68,126 computer-aided interviews were weighted to yield estimates that would be representative for the U.S. population, based on the 2000 census. After processing the data to protect respondent confidentiality (including subsampling, dropping or recoding identifying variables, and reweighting), the final analytic sample size for the 2002 public use file was 54,079 (SAMHSA, 2004b). The 2000 and 2001 surveys followed procedures similar to the 2002 survey’s, except that respondents were not given a gratuity. The 2000 and 2001 surveys had weighted interview response rates of 73–74%. Weights for these survey years were based on population projections from the 1990 census. Because of the above changes to the survey in 2002 and improved data collection procedures beginning in 2001, the 2002 survey marked a new baseline for measuring trends in substance use. Therefore, data from 2002 are not combined with data from prior survey years. The corresponding sample sizes for the 2000 and 2001 public use files were 58,680 and 55,561, respectively, for a combined sample size of 114,241 (SAMHSA, 2004c, 2004d).
2.2. Key definitions Demographic definitions in this report are generally similar to definitions used in NSDUH tables and reports. For health insurance coverage, we created a variable with nonoverlapping categories: (a) private health insurance; (b) Medicaid or the Children’s Health Insurance Program (but no private coverage); (c) any other coverage, such as Medicare (but neither ‘a’ nor ‘b’); (d) no coverage. Population density was defined according to whether persons lived in a large metropolitan area with a population of 1 million or more, a small metropolitan area with a population of less than 1 million, or a nonmetropolitan area.
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Table 1 ADHD stimulants reported in the 2002 NSDUH public use data Druga
Estimated number of lifetime users, in thousands (S.E.)
Durationb
How reported by respondents
Ritalin® or methylphenidate Cylert® Dexedrine® Dextroamphetamine Adderall® DextroStat® Concerta®
4524 (210) 207 (47) 3360 (226) 593 (86) 245 (25) 1 (1)e 5 (2)e
Short-acting Long-acting Short-acting Short-acting Intermediate-acting Short-acting Extended-release
Solicitedc Solicited Solicited Solicited Volunteeredd Volunteered Volunteered
Source: SAMHSA (2003). a Proprietary drug names are listed according to how questions were asked or based on information that respondents volunteered. For example, respondents were asked, “Have you ever, even once, used Ritalin or Methylphenidate that was not prescribed for you or that you took only for the experience or feeling it caused?” Generic (nonproprietary) drug names are not given if respondents were not asked the generic name or if they volunteered a brand name as “some other stimulant” they had used. b Duration of effect between doses, depending on the medication—short-acting: 3–6 h; intermediate-acting: 6–8 h; long-acting or extended-release: 8–12 h (see American Academy of Pediatrics, 2001). c Respondents were asked directly about lifetime nonmedical use of this stimulant. d Reported nonmedical use captured from respondents who specified use of this stimulant as “some other stimulant” they had used. Consequently, these reports are likely to underestimate the true prevalence. e Low precision; use with caution. NSDUH classifies respondents as stimulant misusers if they report using any prescription-type stimulant, even once, without a doctor’s prescription or for the experience or feeling it caused. Thus, the survey specifically assesses prescription drug misuse (i.e., use outside of legitimate therapeutic use). For the purposes of this study, the term misuse hereafter refers to this nonmedical use. Respondents were classified as past-year misusers if they reported that their most recent misuse was within 1 year of the interview date. We created three main measures of past-year misuse from the data: misuse of (a) any stimulant; (b) non-methamphetamine stimulants, which excluded past-year methamphetamine use; (c) ADHD-specific stimulants, defined as stimulants with specific indications for the treatment of ADHD (Table 1). These were binary measures (i.e., measures of either past-year misuse of one or more drugs in the category of interest or no past-year misuse). For the non-methamphetamine measure, we excluded past-year methamphetamine misusers because NSDUH did not distinguish between respondents who misused methamphetamine and those who misused other stimulants in that same period. Thus, the non-methamphetamine measure captured information on respondents whose stimulant misuse in the past year principally or solely involved diverted prescription medications, as opposed to illegally manufactured “street” drugs. Table 1 indicates the specific ADHD stimulants captured in the 2002 data. Again, because the past-year stimulant measure in NSDUH did not differentiate between misuse of ADHD stimulants and misuse of other stimulants in that period, we first identified respondents whose lifetime misuse of stimulants was limited to ADHD stimulants. By definition, past-year users in this subgroup had to have used ADHD stimulants in that period. Unlike the anystimulant and non-methamphetamine measures, the source variables for the ADHD-specific stimulant measure were not statistically imputed to eliminate missing data. This measure was taken for consistency with the NSDUH source variables for lifetime misuse of Ritalin® /methylphenidate, Cylert® , Dexedrine® , and dextroamphetamine, which treated respondents with missing data as equivalent to nonusers. The number of respondents affected by such missing data was low (e.g., only 39 respondents in the 2002 file with missing data for lifetime misuse of Ritalin® /methylphenidate). This assumption introduces some conservative bias into the data, and these estimates should therefore be considered underestimates of the prevalences of actual misuse. The public use files also included variables from non-clinician field survey assessments of stimulant dependence, stimulant abuse, or any stimulant dependence or abuse, based on DSM-IV (American Psychiatric Association, 1994). NSDUH classifies misusers as dependent if they report at least three out of seven DSM-IV dependence criteria for stimulants in the past 12 months. It classifies misusers as abusing if they do not meet the criteria for stimulant dependence but report at least one out of four DSM-IV abuse criteria.
2.3. Analytic approach Analyses consisted of computing weighted population prevalence estimates and estimation of study relationships using logistic regression models. Analyses and tests of statistical significance were performed using SUDAAN Software for Statistical Analysis of Correlated Data (version 8.02) to take into account the sample design (RTI International, 2001). For the analyses of substance dependence and abuse using combined 2000 and 2001 survey data, analysis weights for each year were divided by 2 to produce annual average population counts. We used the standard difference in proportions test to identify statistically significant differences between percentages. Standard NSDUH criteria were implemented to identify unreliable estimates. Estimates deemed unreliable are marked and require cautious interpretation in light of their statistical imprecision. For logistic regression models, past-year misuse measures among persons aged 12 or older served as response variables. We specified separate models for each type of stimulant misuse (any stimulant, non-methamphetamine, and ADHD-specific stimulants). Covariate terms in these regression models included sex of the respondent (male/female), age, self-designated race/ethnicity, population density, family income, family receipt of government benefits, and type of health insurance. Income, receipt of government benefits, and health insurance coverage were not strongly correlated with one another in the data (Pearson correlation coefficients of −0.36 to 0.33). Educational attainment was age dependent and therefore not included.
3. Results In 2002, an estimated 21 million persons aged 12 years or older were found to have misused at least one prescription stimulant at least once in their lifetimes. Most of these persons (15 million, or 70%) had misused stimulants other than methamphetamine at least once. An estimated 7.3 million persons reported misusing ADHD stimulants in their lifetimes, representing 34.7% of all lifetime stimulant misusers and nearly half (49.4%) of those reporting misuse of non-methamphetamine stimulants. Among those reporting misuse of ADHD stimulants in their lifetimes, 2.9 million persons, or 39.3%, had misused ADHD stimulants exclusively. An estimated 2.6% of persons aged 12–17 years and 5.9% of persons aged 18–25 years had
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Table 2 Percentages and estimated numbers (in thousands) of nonmedical stimulant users in the past year, by stimulant category and age group: 2002 Characteristic
Stimulant category Any STIMa
Non-METHb
ADHD STIM onlyc
Percent (S.E.)
Number, in thousands (S.E.)
Percent (S.E.)
Number, in thousands (S.E.)
Percent (S.E.)
Number, in thousands (S.E.)
Total, 12 or older
1.4 (0.07)
3210 (161)
0.7 (0.05)
1618 (108)
0.3 (0.02)
757 (58)
Age group 12–17 18–25 26 or older
2.6 (0.15) 3.7 (0.19) 0.8 (0.08)
640 (38) 1136 (58) 1434 (143)
1.7 (0.12) 2.0 (0.14) 0.3 (0.05)
417 (29) 606 (43) 595 (93)
0.9 (0.09) 1.3 (0.12) 0.1 (0.02)
226 (21) 394 (36) 137 (40)
Gender Male Female
1.5 (0.10) 1.3 (0.08)
1664 (117) 1547 (96)
0.7 (0.07) 0.7 (0.06)
764 (75) 854 (71)
0.4 (0.04) 0.3 (0.03)
453 (44) 304 (34)
Race/ethnicity Not Hispanic White Black Other Hispanic
1.6 (0.08) 0.5 (0.14) 1.0 (0.16) 1.0 (0.23)
2667 (138) 121 (36) 133 (22) 289 (66)
0.9 (0.06) 0.3 (0.10) 0.3 (0.07) 0.3 (0.06)
1409 (101) 79 (26) 43 (9) 87 (18)
0.4 (0.03) 0.0 (0.02) 0.2 (0.06) 0.2 (0.05)
654 (55) 12 (5) 31 (8) 61 (16)
Population density MSA, ≥1 million MSA, <1 million Not in MSA
1.1 (0.09) 1.7 (0.13) 1.4 (0.15)
1140 (90) 1319 (105) 751 (78)
0.5 (0.05) 0.9 (0.08) 0.7 (0.12)
562 (57) 680 (62) 376 (64)
0.3 (0.04) 0.4 (0.05) 0.3 (0.05)
296 (41) 314 (35) 148 (24)
STIM: stimulant; non-METH: non-methamphetamine; ADHD STIM: stimulant used to treat ADHD; MSA: metropolitan statistical area. Source: SAMHSA (2004b). a Estimates for nonmedical stimulant use in this table may differ slightly from published NSDUH estimates because of subsampling and reweighting of data for the public use file. b Used a stimulant nonmedically in the past 12 months but did not use methamphetamine in this period. c Persons who were lifetime nonmedical users only of ADHD stimulants and who used these stimulants nonmedically in the past year.
ever misused ADHD stimulants. In addition, 1.7% of persons aged 12–17 years and 3.5% of persons aged 18–25 years had misused ADHD stimulants exclusively. Misuse of ADHD stimulants most frequently involved methylphenidate and Dexedrine® , but longer-acting formulations were reported as well (Table 1). The numbers of persons reporting misuse of each of these ADHD stimulants in Table 1 sum to more than 7.3 million because persons could be lifetime misusers of more than one ADHD stimulant. Estimated numbers of persons in different categories of pastyear misuse are shown in Table 2. Of the estimated 3.2 million persons who misused any prescription stimulant in the past year, slightly more than half (1.7 million) were aged 12–25 years. However, this age group comprised more than 60% of the 1.6 million misusers of non-methamphetamine stimulants and more than 80% of the 0.8 million misusers of ADHD stimulants. Females comprised fewer than one-half of past-year misusers of any prescription stimulant (1.5 million) and ADHD stimulants (0.3 million) but comprised a slight majority (0.9 million) of misusers of non-methamphetamine stimulants. Selected correlates of different categories of past-year misuse also are shown in Table 2, expressed as percentages of misusers within specific demographic groups. Except where noted, all differences cited in the text were statistically significant at P < 0.05. Any stimulant misuse was more prevalent among persons aged 12–25 years, as compared with older adults. For persons who had misused only ADHD stimulants, young adults aged 18–25
years also had a higher prevalence of misuse in the past year (1.3%), compared with persons aged 26 or older (0.1%) and a slightly higher prevalence compared with persons aged 12–17 years (0.9%). Moreover, misuse of non-methamphetamine stimulants was the predominant form of stimulant misuse among persons aged 12–25. Of the estimated 1.8 million persons in this age group who misused stimulants in the past year, 1.0 million (58%) misused non-methamphetamine stimulants. In addition, most (0.6 million) of the 1.0 million non-methamphetamine stimulant misuse in this age group was exclusively with ADHD stimulants. Females were as likely as males to misuse any stimulant and non-methamphetamine stimulants. However, males had a slightly higher prevalence of ADHD stimulant misuse compared with females. Whites had higher prevalences of misuse of any stimulant, non-methamphetamine stimulants, and ADHD stimulants than did other racial/ethnic groups. The estimate of ADHD stimulant misuse among Blacks was not actually zero but rounded to zero when shown to the nearest tenth of a percent in Table 2. All prevalences for large metropolitan areas were lower than those in small metropolitan areas (P < 0.05). Prevalences of any stimulant misuse also were lower in large metropolitan areas, compared with nonmetropolitan areas; this pattern did not hold for non-methamphetamine and ADHD stimulants. Table 3 presents the covariate-adjusted odds ratios (ORs) for past-year misuse of any stimulants and ADHD stimulants
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Table 3 Adjusted odds ratios for nonmedical use of any stimulants and only ADHD stimulants in the past year among demographic subgroups: 2002 Any stimulant OR (95% CI)a
ADHD stimulant only OR (95% CI)
Gender Male Female
1.13 (0.94–1.36) 1.00 (–)
Age group 12–17 18–25 26 or older
3.53*** (2.77–4.50) 4.06*** (3.16–5.21) 1.00 (–)
13.64*** (7.33–25.36) 16.74*** (9.23–30.33) 1.00 (–)
Race/ethnicity White, not Hispanic Black, not Hispanic Other, not Hispanic Hispanic
1.00 (–) 0.19*** (0.10–0.34) 0.49*** (0.35–0.69) 0.37*** (0.22–0.60)
1.00 (–) 0.10*** (0.04–0.22) 0.44** (0.25–0.76) 0.40** (0.23–0.72)
Population density MSA, ≥1 million MSA, <1 million Not in MSA
0.99 (0.75–1.31) 1.26 (0.98–1.63) 1.00 (–)
1.23 (0.80–1.89) 1.34 (0.91–1.97) 1.00 (–)
Family income Less than US$ 10,000 US$ 10,000–19,999 US$ 20,000–29,999 US$ 30,000–39,999 US$ 40,000–49,999 US$ 50,000–74,999 US$ 75,000 or more
1.75** (1.24–2.48) 1.48* (1.05–2.08) 0.96 (0.68–1.35) 1.17 (0.80–1.71) 1.32 (0.88–1.97) 1.04 (0.76–1.41) 1.00 (–)
1.96** (1.22–3.14) 1.16 (0.69–1.95) 0.91 (0.53–1.57) 0.84 (0.46–1.55) 0.74 (0.37–1.49) 0.69 (0.43–1.10) 1.00 (–)
Family government assistance Yes No
1.45* (1.04–2.03) 1.00 (–)
0.66 (0.42–1.04) 1.00 (–)
Health insurance coverage Private insurance Medicaid or CHIP, not private Other health insuranceb No health insurance
0.47*** (0.35–0.64) 0.64* (0.43–0.97) 0.29*** (0.19–0.44) 1.00 (–)
1.54 (0.99–2.41) 1.16 (0.63–2.13) 1.80 (0.93–3.51) 1.00 (–)
1.52** (1.15–2.00) 1.00 (–)
(–): not applicable (reference group); MSA: metropolitan statistical area; CHIP: Children’s Health Insurance Program. Source: SAMHSA (2004b). a 95% CI: 95% confidence interval of the odds ratio. b Includes reports of Medicare coverage, military coverage for veterans and dependents, or respondents who were otherwise classified as having any coverage besides private health insurance, Medicaid, or CHIP. * P < 0.05 (odds ratio that was statistically significant from the reference group). ** P < 0.01 (odds ratio that was statistically significant from the reference group). *** P < 0.001 (odds ratio that was statistically significant from the reference group).
with respect to key study variables. (Similar models also were run for past-year methamphetamine and non-methamphetamine misuse, but these data are not shown in Table 3.) Consistent with the unadjusted data, the covariate-adjusted estimates showed that persons under the age of 26 years were more likely than their older counterparts to be misusers of any stimulant; the same was found for Whites versus non-Whites. In addition, compared to the experience of older adults, youths and young adults had more than 10 times the odds of being pastyear users of the ADHD stimulants (but not other stimulants). Covariate-adjusted male–female relationships also were consistent with estimates based upon unadjusted data. In addition, males were more likely than females to be past-year methamphetamine misusers (OR = 1.41; P < 0.05). Persons in the lowest income category had higher odds of being misusers of any stimulant and ADHD stimulants relative to persons in the highest
income category. Any stimulant misuse was less likely among persons with health insurance but was more likely among persons in families receiving government assistance; these patterns did not hold in the ADHD-specific stimulant analyses. Misuse of any stimulant and of ADHD-specific stimulants did not differ significantly by population density when the models controlled for the potential confounding effects of other characteristics, such as race/ethnicity. Despite the large sample size for the 2002 public use file, it did not have sufficient numbers of respondents in the stimulant subgroups to estimate dependence or abuse among the following key subgroups of past-year misusers: non-methamphetamine misusers who were aged 26 or older, male, non-White or Hispanic, or living in nonmetropolitan areas; ADHD-only users who were aged 26 or older, non-White or Hispanic, or living in nonmetropolitan areas when the data were subset further
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Table 4 Dependence on or abuse of stimulants in the past year among past-year users, by stimulant category, age group, and gender: 2000 and 2001 Stimulant category/age group/gender
Percent (S.E.) Dependence or abuse
Dependence
Abuse
Any Total, 12 or older 12–17 18–25 26 or older Male, 12 or older Female, 12 or older
13.0 (1.40) 14.3 (1.43) 10.8 (1.22) 14.3 (3.20) 11.8 (2.01) 14.3 (1.92)
9.3 (1.31) 6.2 (0.96) 8.5 (1.10) 12.0 (3.06) 8.1 (1.92) 10.8 (1.75)
3.7 (0.55) 8.1 (1.09) 2.3 (0.58) 2.3 (1.07) 3.7 (0.75) 3.6 (0.79)
Non-METHb Total, 12 or older 12–17 18–25 26 or older Male, 12 or older Female, 12 or older
9.2(1.27) 10.8(1.51) 8.9(1.61) 8.0(3.22) 9.0(1.88) 9.4(1.78)
5.7(1.11) 3.4(0.83) 6.6(1.36) 6.8(3.02) 5.3(1.58) 6.0(1.62)
3.5 (0.66) 7.4 (1.30) 2.3 (0.87) 1.2 (1.20)c 3.6 (1.08) 3.4 (0.77)
2.3 (0.70) 2.2 (0.87) 3.1 (1.29) 0.1 (0.09)c 1.2 (0.63) 3.5 (1.34)
2.5 (0.72) 3.5 (1.21) 2.5 (1.16) 0.0 (0.00)c 3.5 (1.20) 1.2 (0.63)
STIMa
ADHD STIM onlyd Total, 12 or older 12–17 18–25 26 or older Male, 12 or older Female, 12 or older
4.7 (1.03) 5.7 (1.47) 5.6 (1.77) 0.1 (0.09)c 4.7 (1.35) 4.8 (1.49)
Denominators are past-year stimulant users; STIM: stimulant; Non-METH: non-methamphetamine; ADHD STIM: stimulant used to treat ADHD. Source: SAMHSA (2004c,d). a Estimates for nonmedical stimulant use in this table may differ slightly from published NSDUH estimates due to subsampling and reweighting of data for the public use file. b Used a stimulant nonmedically in the past 12 months but did not use methamphetamine in this period. c Low precision; use with caution. d Persons who were lifetime nonmedical users only of stimulants prescribed for ADHD and who used these stimulants nonmedically in the past year.
by demographics. Exploratory analyses of the larger combined 2000 and 2001 data showed patterns of misuse by age group, gender, race/ethnicity, and population density that were similar to those in the 2002 data. For example, an estimated 13% of recent nonmethamphetamine misusers aged 12–17 years in the 2002 data crossed survey-based DSM-IV thresholds for stimulant dependence or abuse but with an associated standard error (S.E.) of 2.5%; the corresponding estimate for the combined 2000 and 2001 data was 10.8% but with an S.E. of only 1.5%. Similarly, 8–9% of non-methamphetamine misusers aged 18–25 years in the 2002 data (S.E.: 1.7%) qualified as cases of survey-assessed dependence or abuse, compared with 8.9% (S.E.: 1.6%) in the combined 2000 and 2001 data. Among female non-methamphetamine misusers, 12% (S.E.: 3%) reported threshold numbers of dependence or abuse symptoms in 2002, compared with 9.4% in the combined 2000 and 2001 data (S.E.: 1.8%). Table 4 presents NSDUH-based estimates of dependence or abuse based on the combined 2000 and 2001 data. An estimated 13% of past-year misusers of any stimulant were classified as meeting criteria for stimulant dependence or abuse. This figure translates to an annual mean value of approximately 303,000 active cases of stimulant dependence or stimulant abuse in the population. About 10% of respondents aged 12–25 years who were past-year misusers of non-methamphetamine stimulants
(75,000 persons) qualified for DSM-IV stimulant dependence or had experienced one or more clinical features of abuse; persons classified as cases of abuse had fewer than three clinical features of dependence. More than half of these non-methamphetamine misusers (39,000) had experienced three or more clinical features of stimulant dependence. Clinical features of stimulant dependence predominated among adult stimulant misusers, and clinical features of abuse predominated among youth. Females who misused stimulants also had somewhat higher prevalences of the survey-assessed stimulant dependence syndrome, as compared with males, though the differences were modest and not statistically significant. Among females who misused ADHDspecific stimulants exclusively, an estimated 8000 had experienced three or more clinical features of DSM-IV stimulant dependence, and an estimated 3000 had experienced fewer than three clinical features of dependence but one or more clinical features of DSM-IV stimulant abuse. These values compare with only 3000 male ADHD-specific stimulant misusers having three or more clinical features of dependence and 10,000 who otherwise had experienced one or more clinical features of DSM-IV stimulant abuse. 4. Discussion Without minimizing concerns about a growing problem of methamphetamine misuse in the United States, our findings
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indicate that most recent stimulant misuse involves the diversion of prescription drugs. Some of the reported lifetime misuse involved newer extended-release stimulants, indicating that longer-acting stimulant formulations are not exempt from misuse. Moreover, most recent stimulant misusers aged 12–25 years exclusively misused prescription (i.e., non-methamphetamine) stimulants. Consistent with NSDUH data on any illegal drug use, pastyear stimulant misuse is more prevalent among persons aged 25 years or younger (SAMHSA, 2004a). This age relationship is even more dramatic among persons whose misuse was limited to ADHD stimulants. There also appear to be gender differences in misuse. Although males and females were equally likely to have used stimulants nonmedically (unlike the situation for any illegal drug use), males were more likely than females to have misused ADHD-specific stimulants. The relative prevalence of stimulant dependence or abuse in the combined 2000 and 2001 survey data also indicates some notable age and gender differences for the ADHD-specific stimulant group, with females somewhat more likely to meet criteria for dependence and males more likely to meet criteria for nondependent abuse. In addition to age and gender differences, some prevalences of misuse were lower in large metropolitan areas, compared with smaller metropolitan or rural areas. Further, rural stimulant misuse is not limited to methamphetamine. These findings run counter to the NSDUH pattern for any illegal drug use, which is less prevalent in rural areas (SAMHSA, 2004a). In comparison, McCabe et al. (2004) reported that 4.1% of a sample of 1536 public school students in grades 6–11 in a large Midwestern city were lifetime misusers of ADHD stimulants. Although their findings may not generalize to the national experience with ADHD stimulants, their finding that Black students were less likely than White students to be ADHD stimulant misusers was consistent with this study’s results from NSDUH. Nonetheless, both our findings and those of McCabe et al. indicate that the prevalence of ADHD stimulant misuse is not a trivial value from the public health perspective. These study data may have important policy and public health implications. First, misuse of these drugs can place increased demand on the health care system, which now faces additional requirements to treat the consequences of stimulant misuse. Many of the prescription stimulants that are assessed in the NSDUH are classified as Schedule II drugs, meaning that they have been judged to have a high potential for dependence or abuse when used outside of appropriate medical supervision. Consistent with this classification, 1 in 10 respondents aged 12–25 years who recently had misused only non-methamphetamine stimulants was identified as dependent on or an abuser of stimulants. Although the higher prevalence of dependence among females was not significantly different from the corresponding prevalence for males, the findings are not dissimilar from estimates provided via other research, showing an increased risk for dependence among females (Wu and Schlenger, 2003). Second, diverted medicines by definition do not benefit the patients who are intended to be using them. Thus, the health care system still faces the burden of responding to disorders that are undertreated or not treated at all.
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An additional concern is the potential for diversion when students take ADHD medications to school or are dosed during school hours. For example, students may sell medications to classmates or steal them from classmates or from the school. Approximately 8% of public middle and high schools reported at least one episode of diversion of these medications during the 2000–2001 school year, and most of these diversion episodes at school involved students selling or giving their medications to classmates (United States General Accounting Office, 2001). McCabe et al. (2004) reported that nearly one-fourth of the students in their sample who had been prescribed ADHD stimulants had been approached at least once to sell, trade, or give away their medications. Although it is tempting to make specific recommendations regarding policies for prescribing or using stimulants based on these data, it is important to remember that the current data address only the demand side of the drug diversion problem, not the supply side (e.g., how these drugs are being diverted). Specific recommendations for policy change would require more complete examination of both the supply and demand sides of the problem—i.e., more than these data can provide. Nevertheless, the current data indicate that the misuse of stimulants associated with the diversion of prescription medicines is substantial enough to merit follow-up work in this area. The concerns about diversion of prescription stimulants should not be construed as recommendations against the use of these medications to treat ADHD or other disorders under appropriate medical supervision. As noted previously, the benefits of these medications to treat ADHD are widely recognized, including benefits for treatment of ADHD in adults (Goldman et al., 1998; Faraone et al., 2004; Hechtman and Greenfield, 2003; Kociancic et al., 2004). Several recent studies have indicated no increased risk for substance experimentation or disorders among youth who were treated with stimulants for ADHD, or reduced risk relative to persons whose ADHD was not treated pharmacologically (Barkley et al., 2003; Fischer and Barkley, 2003; Biederman, 2003; Wilens et al., 2003). Such findings are not counter to the present findings because stimulant misusers in NSDUH were not asked about treatment for ADHD. Furthermore, Fischer and Barkley (2003) controlled for conduct disorder in their analyses. If youth with conduct disorder also are misusing prescription stimulants, they could be at increased risk for substance use disorders. An important strength of this study is that estimates are based on nationally representative data that reduce constraints upon inferences to be made about nonmedical stimulant use in the general U.S. population. Further, the survey methods provided a way for respondents to report sensitive behaviors confidentially and allowed respondents with limited reading ability to listen to the questions on headphones. As noted in Section 2, the computer-assisted design also improved data quality by reducing opportunities for respondents to give inconsistent answers (Kroutil and Handley, 2004). In addition, the large sample size in 2002 provided sufficient numbers of nonmedical stimulant users in the data to examine correlates of use, even when the data were further subdivided by demographic characteristics. Although the 2002 sample did not
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provide sufficient precision for examining stimulant dependence or abuse among subgroups of nonmedical users, the availability of common measures facilitated pooling of the data from 2000 and 2001. Limitations of the study include the cross-sectional design, which allows associations to be identified but constrains causal inferences, and reliance on respondent self-reports. The latter may result in underestimates or overestimates of prevalence, depending on circumstances and processes such as respondent recall and willingness to report nonmedical use. In particular, respondents with limited reading or spelling ability or low motivation to disclose substance use could underreport the misuse of “other” stimulants for which they had to type in the names (see Table 1). This study also shared the limitations inherent in any secondary analysis of data—namely, that the variables and measures in the data set were not developed with these analyses in mind. Specifically, measures for nonmedical use of most specific stimulants (e.g., methylphenidate) were limited to lifetime use. Although the NSDUH data permitted identification of subgroups such as persons who had not used methamphetamine in the past year or had used only ADHD stimulants, the data did not permit identification of persons who may have used more than one type of stimulant in the past year. Our findings highlight the magnitude of ADHD stimulant misuse in the United States and raise important new questions. Future research might examine, for example, the past-year use of specific stimulants other than methamphetamine (with or without use of methamphetamine in that same period), which would help differentiate between persons who use any available stimulant and those who have clear preferences for certain types of stimulants. In addition, information on how nonmedical users obtain stimulants would allow the relative importance of specific sources of diversion to be estimated and would be helpful in determining who bears the economic burden of misuse. Further research on motivations for misusing stimulants, such as expectations of weight control or improved academic performance, could be helpful in designing appropriate prevention programs. Longitudinal research on nonmedical use of prescription stimulants also would be important in identifying individual-level changes in patterns of use over time. For example, longitudinal evidence would help to clarify whether persons who start out using diverted prescription medications move toward using street drugs later in life. Acknowledgements Study design and data collection were done by the Substance Abuse and Mental Health Services Administration. The current analysis was sponsored by Eli Lilly and Company. References American Psychiatric Association, 1994. Diagnostic and Statistical Manual of Mental Disorders, 4th ed. American Psychiatric Association, Washington, DC. American Academy of Pediatrics, Subcommittee on AttentionDeficit/Hyperactivity Disorder, Committee on Quality Improvement, 2001. Clinical practice guideline: treatment of the school-aged child
with attention-deficit/hyperactivity disorder. Pediatrics 108 (4), 1033– 1044. Barkley, R.A., Fischer, M., Smallish, L., Fletcher, K., 2003. Does the treatment of attention-deficit/hyperactivity disorder with stimulants contribute to drug use/abuse? A 13-year prospective study. Pediatrics 111, 97–109. Barkley, R.A., McMurray, M.B., Edelbrock, C.S., Robbins, K., 1990. Side effects of methylphenidate in children with attention deficit hyperactivity disorder: a systemic, placebo-controlled evaluation. Pediatrics 86, 184–192. Biederman, J., 2003. Pharmacotherapy for attention-deficit/hyperactivity disorder (ADHD) decreases the risk for substance abuse: findings from a longitudinal follow-up of youths with and without ADHD. J. Clin. Psychiatry 64 (Suppl. 11), 3–8. Degrandpre, R., 2000. Ritalin Nation: Rapid-Fire Culture and the Transformation of Human Consciousness. W.W. Norton & Company, New York. Drug and Alcohol Services Information System, 2004. Primary Methamphetamine/Amphetamine Treatment Admissions: 1992–2002. Faraone, S.V., Spencer, T., Aleardi, M., Pagano, C., Biederman, J., 2004. Meta-analysis of the efficacy of methylphenidate for treating adult attention-deficit/hyperactivity disorder. J. Clin. Psychopharmacol. 24, 24–29. Fischer, M., Barkley, R.A., 2003. Childhood stimulant treatment and risk for later substance abuse. J. Clin. Psychiatry 64 (Suppl 11), 19–23. Goldman, L.S., Genel, M., Bezman, R.J., Slanetz, P.J., 1998. Diagnosis and treatment of attention-deficit/hyperactivity disorder in children and adolescents. Council on Scientific Affairs, American Medical Association. JAMA 279, 1100–1107. Hechtman, L., Greenfield, B., 2003. Long-term use of stimulants in children with attention-deficit hyperactivity disorder: safety, efficacy, and long-term outcome. Paediatr. Drugs 5, 787–794. Kociancic, T., Reed, M.D., Findling, R.L., 2004. Evaluation of risks associated with short- and long-term psychostimulant therapy for treatment of ADHD in children. Expert. Opin. Drug Saf. 3, 93–100. Kroutil, L.A., Handley, W., 2004. General Principles and Procedures for Editing Drug Use Data in the 2002 NSDUH Computer-Assisted Interview. In 2002 National Survey on Drug Use and Health: Methodological resource book (prepared for the Substance Abuse and Mental Health Services Administration under Contract No. 283-98-9008). RTI International, Research Triangle Park, NC (available at http://www.drugabusestatistics. samhsa.gov/nhsda/2k2MRB/2k2EditsCore.pdf). McCabe, S.E., Teter, C.J., Boyd, C.J., 2004. The use, misuse and diversion of prescription stimulants among middle and high school students. Subst. Use Missue 39, 1095–1116. Robison, L.M., Sclar, D.A., Skaer, T.L., Galin, R.S., 1999. National trends in the prevalence of attention-deficit/hyperactivity disorder and the prescribing of methylphenidate among school-age children: 1990–1995. Clin. Pediatr. (PA) 38, 209–217. RTI International, 2001. SUDAAN User’s Manual: Release 8.0. RTI International, Research Triangle Park, NC. Stockl, K.M., Hughes, T.E., Jarrar, M.A., Secnik, K., Perwien, A.R., 2003. Physician perceptions of the use of medications for attention deficit hyperactivity disorder. J. Manage. Care Pharm. 9, 416–423. Strom, K.J., Wong, L., Fornnarino, L., Eicheldinger, C., Bethke, A., Ancheta, J., Rachal, V., 2004. The National Forensic Laboratory Information System: 2003 Annual Report. U.S. Drug Enforcement Administration, Washington, DC. Substance Abuse and Mental Health Services Administration (SAMHSA), 2003. Results from the 2002 National Survey on Drug Use and Health: National Findings. Substance Abuse and Mental Health Services Administration, Rockville, MD (Office of Applied Studies, NSDUH Series H-22, DHHS Publication No. SMA 03-3836). Substance Abuse and Mental Health Services Administration (SAMHSA), 2004a. Results from the 2003 National Survey on Drug Use and Health: Detailed Tables. Accessed October 8, 2004, at: http://www. drugabusestatistics.samhsa.gov/nhsda/2k3tabs/PDF/2k3tabs.pdf. Substance Abuse and Mental Health Services Administration (SAMHSA), Office of Applied Studies, 2004b. National Survey on Drug Use and Health, 2002 (computer file), second ICPSR version. Research Triangle
L.A. Kroutil et al. / Drug and Alcohol Dependence 84 (2006) 135–143 Institute (producer), Research Triangle Park, NC, 2004. Inter-university Consortium for Political and Social Research (distributor) Ann Arbor, MI (available at http://www.icpsr.umich.edu/SAMHDA/). Substance Abuse and Mental Health Services Administration (SAMHSA), Office of Applied Studies, 2004c. National Household Survey on Drug Abuse, 2000 (computer file), third ICPSR version. Research Triangle Institute (producer), Research Triangle Park, NC, 2004. Inter-university Consortium for Political and Social Research (distributor), Ann Arbor, MI (available at http://www.icpsr.umich.edu/SAMHDA/). Substance Abuse and Mental Health Services Administration (SAMHSA), Office of Applied Studies, 2004d. National Household Survey on Drug Abuse, 2001 (Computer file), second ICPSR version. Research Triangle Institute (producer), Research Triangle Park, NC, 2002. Inter-university Consortium for Political and Social Research (distributor), Ann Arbor, MI (available at http://www.icpsr.umich.edu/SAMHDA/). Substance Abuse and Mental Health Services Administration (SAMHSA), 2005. Results from the 2004 National Survey on Drug Use and Health: National Findings (Office of Applied Studies, NSDUH Series H-28, DHHS Publication No. SMA 05-4062), Rockville, MD. United States Food and Drug Administration, 2005a. Public Health Advisory for Adderall and Adderall XR. Accessed August 24, 2005 at: http://www.fda.gov/cder/drug/advisory/adderall.htm.
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United States Food and Drug Administration, 2005b. Statement on Concerta and Methylphenidate for the June 30, 2005 Pediatric Advisory Committee. Accessed August 24, 2005 at: http://www.fda.gov/ohrms/dockets/ac/05/ slides/2005-4152s2 07 Murphy.ppt. United States General Accounting Office, 2001. Attention Disorder Drugs: Few Incidents of Diversion or Abuse Identified by Schools (GAO-01-1011). United States General Accounting Office, Washington, DC. Wilens, T.E., Faraone, S.V., Biederman, J., Gunawardene, S., 2003. Does stimulant therapy of attention-deficit/hyperactivity disorder beget later substance abuse? A meta-analytic review of the literature. Pediatrics 111, 179–185. Woodworth, T., 2000. Statement of Terrance Woodworth, Deputy Director, Office of Diversion Control, Drug Enforcement Administration, before the Committee on Education and the Workforce, Subcommittee on Early Childhood, Youth, and Families, May 16, 2000. Wu, L.T., Schlenger, W.E., 2003. Psychostimulant dependence in a community sample. Subst. Use Misuse 38, 221–248. Zamiska, N., 2004. Pressed to do well on admissions tests, students take drugs—stimulants prescribed for attention disorders find new unapproved use. The Wall Street Journal. A1 ed., November 8, 2004.
Nonmedical use of prescription stimulants in the United States夽 Larry A. Kroutil a,∗ , David L. Van Brunt b , Mindy A. Herman-Stahl a , David C. Heller a , Robert M. Bray a , Michael A. Penne a b
a RTI International, 3040 Cornwallis Road, Research Triangle Park, NC 27709, USA Lilly Research Laboratories, Lilly Corporate Center, DC0825, Indianapolis, IN 46285, USA
Received 17 June 2005; received in revised form 17 December 2005; accepted 21 December 2005
Abstract Objective: This study estimated prevalences and correlates of stimulant diversion in the United States and examined relationships between diversion and measures of abuse or dependence. Methods: We conducted descriptive and multivariate analysis of data from the National Survey on Drug Use and Health. Key measures were nonmedical use (misuse) of any prescription stimulant, any stimulant other than methamphetamine, and stimulants indicated for attentiondeficit/hyperactivity disorder (ADHD). Results: Lifetime stimulant misuse included some misuse of longer-acting ADHD drugs. The majority of past-year misuse involved drugs other than methamphetamine, particularly for youth aged 12–17. Past year misuse was more prevalent among persons aged 12–25, compared with older adults, and among Whites, compared with other groups. Prevalences in large metropolitan areas were lower than or similar to those in less populated areas. About 13% of past-year stimulant misusers met the survey criteria for dependence or abuse, as did about 10% of persons aged 12–25 who misused only nonmethamphetamine stimulants. Conclusions: Most stimulant misuse in the United States (particularly among youth) involved prescription drugs other than methamphetamine. The problem is not limited to metropolitan areas. © 2006 Elsevier Ireland Ltd. All rights reserved. Keywords: Attention-deficit/hyperactivity disorder (ADHD); Stimulants; Methamphetamine; Nonmedical use; Correlates
1. Introduction Stimulants are prescribed for effective treatment of a variety of medical conditions, including narcolepsy, attentiondeficit/hyperactivity disorder (ADHD), and obesity. Despite the therapeutic value of these medications, concerns have arisen about their diversion for nonmedical use (i.e., misuse). In 1998, 夽 Findings that were recently released from the 2004 NSDUH, subsequent to the initial preparation of this manuscript, indicated that the prevalences of past-year misuse of any stimulant and of methamphetamine have been stable from 2002 through 2004 for persons aged 12 years or older and among adult age groups. Among youths aged 12–17 years, however, the past-year prevalence of any stimulant misuse in 2004 (2.0%) was found to be significantly lower than the prevalence in 2002 (P < 0.01); the prevalence in 2003 and 2004 was stable [see SAMHSA, 2005. Results from the 2004 National Survey on Drug Use and Health: National Findings. Author, Rockville, MD (Office of Applied Studies, NSDUH Series H-28, DHHS Publication No. SMA 05-4062)]. ∗ Corresponding author. Tel.: +1 919 541 6067; fax: +1 919 485 5555. E-mail address: [email protected] (L.A. Kroutil).
0376-8716/$ – see front matter © 2006 Elsevier Ireland Ltd. All rights reserved. doi:10.1016/j.drugalcdep.2005.12.011
Goldman et al. conducted a review on ADHD, motivated in part by public concern surrounding the increase in production and use of methylphenidate (Ritalin) and resulting questions about the prevalence of diversion. This study concluded that stimulant misuse and diversion were not a major problem at the time but speculated that trends toward expanding production could increase diversion in the future. According to the Drug Enforcement Administration, the methylphenidate production quota (i.e., the amount approved for manufacturing) increased from 1768 kg in 1990 to 14,957 kg in 2000 (Woodworth, 2000). Concomitantly, the number of adolescents and adults being treated for ADHD with prescription stimulants has risen steadily since 1990 (Goldman et al., 1998; Robison et al., 1999). In a recent survey of physicians, 19% reported concern over stimulant diversion for nonmedical use, notwithstanding the established efficacy of stimulants for the treatment of ADHD (Stockl et al., 2003). Concern over the misuse of these medications has garnered popular media attention as well (Zamiska, 2004; Degrandpre, 2000).
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Public health concern is warranted, as both treatment admissions and law enforcement data suggest that problems relating to nonmedical stimulant use are increasing (Drug and Alcohol Services Information System, 2004; Strom et al., 2004). Further, the side effects of legitimate medical use of ADHD stimulants can be sufficiently serious to warrant immediate discontinuation (Barkley et al., 1990). In early 2005, the U.S. Food and Drug Administration (FDA, 2005a) issued a public health advisory for two amphetamine products used to treat ADHD, Adderall® and Adderall XR® , due to reports of sudden, unexplained deaths of pediatric patients taking these medications. In June 2005, the Pediatric Advisory Committee to the FDA (2005b) reported concerns about potential adverse psychiatric or cardiovascular events associated with methylphenidate products; the FDA indicated plans to make labeling changes to describe these events. Given the potential for serious side effects among patients taking these medications under medical supervision, there is even more reason for concern about adverse physical or psychiatric problems associated with use of these medications outside of any such supervision. Recent data from the National Survey on Drug Use and Health (NSDUH, formerly the National Household Survey on Drug Abuse [NHSDA]) indicate that an estimated 21 million persons aged 12 or older in the United States, or about 9%, have used prescription stimulants nonmedically at some point in their lifetimes. This estimate includes an estimated 12 million persons reporting nonmedical use of methamphetamine, which is often produced illegally. In both 2002 and 2003, however, more than half of the target population who used stimulants nonmedically in the past year reported using stimulants other than methamphetamine (Substance Abuse and Mental Health Services Administration [SAMHSA], 2004a). Despite evidence of nonmedical stimulant use by a substantial number of persons, little is known about the types of stimulants that are misused, the characteristics of these users, and associated problems. Although the published reports of findings from NSDUH cover a broad spectrum of substances, these reports present no more than limited descriptive information on misuse of any prescription stimulants relative to misuse of methamphetamine. Further, these reports do not provide informative demographic breakdowns that distinguish prescription stimulants as a group from street drugs. Nor do these standard reports offer covariate-adjusted comparisons of these prevalences. Therefore, the present study addresses gaps in knowledge about prescription stimulant misuse by analyzing NSDUH data in greater detail. We focus on non-methamphetamine and ADHD-specific drugs. The study objectives were to identify (a) important demographic and geographic correlates of nonmedical stimulant use for users of different subtypes of stimulants, (b) correlates of nonmedical use when potential confounding factors are taken into account, and (c) relationships linking different subtypes of nonmedical stimulant use with survey-based syndromes of Diagnostic and Statistical Manual of Mental Disorders (DSM-IV) drug dependence or abuse (American Psychiatric Association, 1994).
2. Methods 2.1. Data sources We used the public use file from the 2002 NSDUH, an annual survey of the civilian, noninstitutionalized population aged 12 or older in the United States (excluding homeless people not living in shelters), as our principal data source (SAMHSA, 2003). We used the combined 2000 and 2001 NSDUH public use files for analyses of substance dependence or abuse because the 2002 file did not contain adequate numbers of respondents for reliable estimation of the prevalence of dependence or abuse clinical features among important subgroups of stimulant misusers. All data files were converted into SAS Version 8 data files for analysis. NSDUH uses a multistage, probability sampling design. Selection of dwelling units in all 50 states and the District of Columbia is followed by inperson screening of sampled dwelling units to identify eligible members aged 12 or older, then random selection of eligible household residents for interview. Interviews are conducted over the course of the year. Respondents in 2002 were given a US$30 gratuity for participation. NSDUH respondents are typically interviewed in their homes. Questions about drug use (including nonmedical stimulant use) and other sensitive behaviors are self-administered using audio computer-assisted self-interviewing. The computer-assisted design reduces opportunities for inconsistent answers by skipping respondents out of questions that do not apply, based on respondents’ prior answers. The occurrence of inconsistent data is further reduced through the use of consistency checks built into the questionnaire program for key items. These consistency checks alert respondents when they have entered an answer that is inconsistent with a previous answer (e.g., misuse of methamphetamine in a more recent period than the most recent period reported for misuse of any stimulant), thereby providing respondents with an opportunity to resolve inconsistencies while the interview is in progress (Kroutil and Handley, 2004). These interview design features do not eliminate missing data, however, because respondents can indicate that they do not know an answer or can refuse to answer. Further, the consistency checks mentioned above do not cover every possible inconsistency in the drug use questions. Therefore, when drug use data are missing or ambiguous, statistical imputation procedures are used to classify respondents as users or nonusers or to assign a definite period when they last used a given drug. The 2002 NSDUH had a weighted screening response rate of 91% and a weighted interview response rate of 79%. Data from a total final sample of 68,126 computer-aided interviews were weighted to yield estimates that would be representative for the U.S. population, based on the 2000 census. After processing the data to protect respondent confidentiality (including subsampling, dropping or recoding identifying variables, and reweighting), the final analytic sample size for the 2002 public use file was 54,079 (SAMHSA, 2004b). The 2000 and 2001 surveys followed procedures similar to the 2002 survey’s, except that respondents were not given a gratuity. The 2000 and 2001 surveys had weighted interview response rates of 73–74%. Weights for these survey years were based on population projections from the 1990 census. Because of the above changes to the survey in 2002 and improved data collection procedures beginning in 2001, the 2002 survey marked a new baseline for measuring trends in substance use. Therefore, data from 2002 are not combined with data from prior survey years. The corresponding sample sizes for the 2000 and 2001 public use files were 58,680 and 55,561, respectively, for a combined sample size of 114,241 (SAMHSA, 2004c, 2004d).
2.2. Key definitions Demographic definitions in this report are generally similar to definitions used in NSDUH tables and reports. For health insurance coverage, we created a variable with nonoverlapping categories: (a) private health insurance; (b) Medicaid or the Children’s Health Insurance Program (but no private coverage); (c) any other coverage, such as Medicare (but neither ‘a’ nor ‘b’); (d) no coverage. Population density was defined according to whether persons lived in a large metropolitan area with a population of 1 million or more, a small metropolitan area with a population of less than 1 million, or a nonmetropolitan area.
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Table 1 ADHD stimulants reported in the 2002 NSDUH public use data Druga
Estimated number of lifetime users, in thousands (S.E.)
Durationb
How reported by respondents
Ritalin® or methylphenidate Cylert® Dexedrine® Dextroamphetamine Adderall® DextroStat® Concerta®
4524 (210) 207 (47) 3360 (226) 593 (86) 245 (25) 1 (1)e 5 (2)e
Short-acting Long-acting Short-acting Short-acting Intermediate-acting Short-acting Extended-release
Solicitedc Solicited Solicited Solicited Volunteeredd Volunteered Volunteered
Source: SAMHSA (2003). a Proprietary drug names are listed according to how questions were asked or based on information that respondents volunteered. For example, respondents were asked, “Have you ever, even once, used Ritalin or Methylphenidate that was not prescribed for you or that you took only for the experience or feeling it caused?” Generic (nonproprietary) drug names are not given if respondents were not asked the generic name or if they volunteered a brand name as “some other stimulant” they had used. b Duration of effect between doses, depending on the medication—short-acting: 3–6 h; intermediate-acting: 6–8 h; long-acting or extended-release: 8–12 h (see American Academy of Pediatrics, 2001). c Respondents were asked directly about lifetime nonmedical use of this stimulant. d Reported nonmedical use captured from respondents who specified use of this stimulant as “some other stimulant” they had used. Consequently, these reports are likely to underestimate the true prevalence. e Low precision; use with caution. NSDUH classifies respondents as stimulant misusers if they report using any prescription-type stimulant, even once, without a doctor’s prescription or for the experience or feeling it caused. Thus, the survey specifically assesses prescription drug misuse (i.e., use outside of legitimate therapeutic use). For the purposes of this study, the term misuse hereafter refers to this nonmedical use. Respondents were classified as past-year misusers if they reported that their most recent misuse was within 1 year of the interview date. We created three main measures of past-year misuse from the data: misuse of (a) any stimulant; (b) non-methamphetamine stimulants, which excluded past-year methamphetamine use; (c) ADHD-specific stimulants, defined as stimulants with specific indications for the treatment of ADHD (Table 1). These were binary measures (i.e., measures of either past-year misuse of one or more drugs in the category of interest or no past-year misuse). For the non-methamphetamine measure, we excluded past-year methamphetamine misusers because NSDUH did not distinguish between respondents who misused methamphetamine and those who misused other stimulants in that same period. Thus, the non-methamphetamine measure captured information on respondents whose stimulant misuse in the past year principally or solely involved diverted prescription medications, as opposed to illegally manufactured “street” drugs. Table 1 indicates the specific ADHD stimulants captured in the 2002 data. Again, because the past-year stimulant measure in NSDUH did not differentiate between misuse of ADHD stimulants and misuse of other stimulants in that period, we first identified respondents whose lifetime misuse of stimulants was limited to ADHD stimulants. By definition, past-year users in this subgroup had to have used ADHD stimulants in that period. Unlike the anystimulant and non-methamphetamine measures, the source variables for the ADHD-specific stimulant measure were not statistically imputed to eliminate missing data. This measure was taken for consistency with the NSDUH source variables for lifetime misuse of Ritalin® /methylphenidate, Cylert® , Dexedrine® , and dextroamphetamine, which treated respondents with missing data as equivalent to nonusers. The number of respondents affected by such missing data was low (e.g., only 39 respondents in the 2002 file with missing data for lifetime misuse of Ritalin® /methylphenidate). This assumption introduces some conservative bias into the data, and these estimates should therefore be considered underestimates of the prevalences of actual misuse. The public use files also included variables from non-clinician field survey assessments of stimulant dependence, stimulant abuse, or any stimulant dependence or abuse, based on DSM-IV (American Psychiatric Association, 1994). NSDUH classifies misusers as dependent if they report at least three out of seven DSM-IV dependence criteria for stimulants in the past 12 months. It classifies misusers as abusing if they do not meet the criteria for stimulant dependence but report at least one out of four DSM-IV abuse criteria.
2.3. Analytic approach Analyses consisted of computing weighted population prevalence estimates and estimation of study relationships using logistic regression models. Analyses and tests of statistical significance were performed using SUDAAN Software for Statistical Analysis of Correlated Data (version 8.02) to take into account the sample design (RTI International, 2001). For the analyses of substance dependence and abuse using combined 2000 and 2001 survey data, analysis weights for each year were divided by 2 to produce annual average population counts. We used the standard difference in proportions test to identify statistically significant differences between percentages. Standard NSDUH criteria were implemented to identify unreliable estimates. Estimates deemed unreliable are marked and require cautious interpretation in light of their statistical imprecision. For logistic regression models, past-year misuse measures among persons aged 12 or older served as response variables. We specified separate models for each type of stimulant misuse (any stimulant, non-methamphetamine, and ADHD-specific stimulants). Covariate terms in these regression models included sex of the respondent (male/female), age, self-designated race/ethnicity, population density, family income, family receipt of government benefits, and type of health insurance. Income, receipt of government benefits, and health insurance coverage were not strongly correlated with one another in the data (Pearson correlation coefficients of −0.36 to 0.33). Educational attainment was age dependent and therefore not included.
3. Results In 2002, an estimated 21 million persons aged 12 years or older were found to have misused at least one prescription stimulant at least once in their lifetimes. Most of these persons (15 million, or 70%) had misused stimulants other than methamphetamine at least once. An estimated 7.3 million persons reported misusing ADHD stimulants in their lifetimes, representing 34.7% of all lifetime stimulant misusers and nearly half (49.4%) of those reporting misuse of non-methamphetamine stimulants. Among those reporting misuse of ADHD stimulants in their lifetimes, 2.9 million persons, or 39.3%, had misused ADHD stimulants exclusively. An estimated 2.6% of persons aged 12–17 years and 5.9% of persons aged 18–25 years had
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Table 2 Percentages and estimated numbers (in thousands) of nonmedical stimulant users in the past year, by stimulant category and age group: 2002 Characteristic
Stimulant category Any STIMa
Non-METHb
ADHD STIM onlyc
Percent (S.E.)
Number, in thousands (S.E.)
Percent (S.E.)
Number, in thousands (S.E.)
Percent (S.E.)
Number, in thousands (S.E.)
Total, 12 or older
1.4 (0.07)
3210 (161)
0.7 (0.05)
1618 (108)
0.3 (0.02)
757 (58)
Age group 12–17 18–25 26 or older
2.6 (0.15) 3.7 (0.19) 0.8 (0.08)
640 (38) 1136 (58) 1434 (143)
1.7 (0.12) 2.0 (0.14) 0.3 (0.05)
417 (29) 606 (43) 595 (93)
0.9 (0.09) 1.3 (0.12) 0.1 (0.02)
226 (21) 394 (36) 137 (40)
Gender Male Female
1.5 (0.10) 1.3 (0.08)
1664 (117) 1547 (96)
0.7 (0.07) 0.7 (0.06)
764 (75) 854 (71)
0.4 (0.04) 0.3 (0.03)
453 (44) 304 (34)
Race/ethnicity Not Hispanic White Black Other Hispanic
1.6 (0.08) 0.5 (0.14) 1.0 (0.16) 1.0 (0.23)
2667 (138) 121 (36) 133 (22) 289 (66)
0.9 (0.06) 0.3 (0.10) 0.3 (0.07) 0.3 (0.06)
1409 (101) 79 (26) 43 (9) 87 (18)
0.4 (0.03) 0.0 (0.02) 0.2 (0.06) 0.2 (0.05)
654 (55) 12 (5) 31 (8) 61 (16)
Population density MSA, ≥1 million MSA, <1 million Not in MSA
1.1 (0.09) 1.7 (0.13) 1.4 (0.15)
1140 (90) 1319 (105) 751 (78)
0.5 (0.05) 0.9 (0.08) 0.7 (0.12)
562 (57) 680 (62) 376 (64)
0.3 (0.04) 0.4 (0.05) 0.3 (0.05)
296 (41) 314 (35) 148 (24)
STIM: stimulant; non-METH: non-methamphetamine; ADHD STIM: stimulant used to treat ADHD; MSA: metropolitan statistical area. Source: SAMHSA (2004b). a Estimates for nonmedical stimulant use in this table may differ slightly from published NSDUH estimates because of subsampling and reweighting of data for the public use file. b Used a stimulant nonmedically in the past 12 months but did not use methamphetamine in this period. c Persons who were lifetime nonmedical users only of ADHD stimulants and who used these stimulants nonmedically in the past year.
ever misused ADHD stimulants. In addition, 1.7% of persons aged 12–17 years and 3.5% of persons aged 18–25 years had misused ADHD stimulants exclusively. Misuse of ADHD stimulants most frequently involved methylphenidate and Dexedrine® , but longer-acting formulations were reported as well (Table 1). The numbers of persons reporting misuse of each of these ADHD stimulants in Table 1 sum to more than 7.3 million because persons could be lifetime misusers of more than one ADHD stimulant. Estimated numbers of persons in different categories of pastyear misuse are shown in Table 2. Of the estimated 3.2 million persons who misused any prescription stimulant in the past year, slightly more than half (1.7 million) were aged 12–25 years. However, this age group comprised more than 60% of the 1.6 million misusers of non-methamphetamine stimulants and more than 80% of the 0.8 million misusers of ADHD stimulants. Females comprised fewer than one-half of past-year misusers of any prescription stimulant (1.5 million) and ADHD stimulants (0.3 million) but comprised a slight majority (0.9 million) of misusers of non-methamphetamine stimulants. Selected correlates of different categories of past-year misuse also are shown in Table 2, expressed as percentages of misusers within specific demographic groups. Except where noted, all differences cited in the text were statistically significant at P < 0.05. Any stimulant misuse was more prevalent among persons aged 12–25 years, as compared with older adults. For persons who had misused only ADHD stimulants, young adults aged 18–25
years also had a higher prevalence of misuse in the past year (1.3%), compared with persons aged 26 or older (0.1%) and a slightly higher prevalence compared with persons aged 12–17 years (0.9%). Moreover, misuse of non-methamphetamine stimulants was the predominant form of stimulant misuse among persons aged 12–25. Of the estimated 1.8 million persons in this age group who misused stimulants in the past year, 1.0 million (58%) misused non-methamphetamine stimulants. In addition, most (0.6 million) of the 1.0 million non-methamphetamine stimulant misuse in this age group was exclusively with ADHD stimulants. Females were as likely as males to misuse any stimulant and non-methamphetamine stimulants. However, males had a slightly higher prevalence of ADHD stimulant misuse compared with females. Whites had higher prevalences of misuse of any stimulant, non-methamphetamine stimulants, and ADHD stimulants than did other racial/ethnic groups. The estimate of ADHD stimulant misuse among Blacks was not actually zero but rounded to zero when shown to the nearest tenth of a percent in Table 2. All prevalences for large metropolitan areas were lower than those in small metropolitan areas (P < 0.05). Prevalences of any stimulant misuse also were lower in large metropolitan areas, compared with nonmetropolitan areas; this pattern did not hold for non-methamphetamine and ADHD stimulants. Table 3 presents the covariate-adjusted odds ratios (ORs) for past-year misuse of any stimulants and ADHD stimulants
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Table 3 Adjusted odds ratios for nonmedical use of any stimulants and only ADHD stimulants in the past year among demographic subgroups: 2002 Any stimulant OR (95% CI)a
ADHD stimulant only OR (95% CI)
Gender Male Female
1.13 (0.94–1.36) 1.00 (–)
Age group 12–17 18–25 26 or older
3.53*** (2.77–4.50) 4.06*** (3.16–5.21) 1.00 (–)
13.64*** (7.33–25.36) 16.74*** (9.23–30.33) 1.00 (–)
Race/ethnicity White, not Hispanic Black, not Hispanic Other, not Hispanic Hispanic
1.00 (–) 0.19*** (0.10–0.34) 0.49*** (0.35–0.69) 0.37*** (0.22–0.60)
1.00 (–) 0.10*** (0.04–0.22) 0.44** (0.25–0.76) 0.40** (0.23–0.72)
Population density MSA, ≥1 million MSA, <1 million Not in MSA
0.99 (0.75–1.31) 1.26 (0.98–1.63) 1.00 (–)
1.23 (0.80–1.89) 1.34 (0.91–1.97) 1.00 (–)
Family income Less than US$ 10,000 US$ 10,000–19,999 US$ 20,000–29,999 US$ 30,000–39,999 US$ 40,000–49,999 US$ 50,000–74,999 US$ 75,000 or more
1.75** (1.24–2.48) 1.48* (1.05–2.08) 0.96 (0.68–1.35) 1.17 (0.80–1.71) 1.32 (0.88–1.97) 1.04 (0.76–1.41) 1.00 (–)
1.96** (1.22–3.14) 1.16 (0.69–1.95) 0.91 (0.53–1.57) 0.84 (0.46–1.55) 0.74 (0.37–1.49) 0.69 (0.43–1.10) 1.00 (–)
Family government assistance Yes No
1.45* (1.04–2.03) 1.00 (–)
0.66 (0.42–1.04) 1.00 (–)
Health insurance coverage Private insurance Medicaid or CHIP, not private Other health insuranceb No health insurance
0.47*** (0.35–0.64) 0.64* (0.43–0.97) 0.29*** (0.19–0.44) 1.00 (–)
1.54 (0.99–2.41) 1.16 (0.63–2.13) 1.80 (0.93–3.51) 1.00 (–)
1.52** (1.15–2.00) 1.00 (–)
(–): not applicable (reference group); MSA: metropolitan statistical area; CHIP: Children’s Health Insurance Program. Source: SAMHSA (2004b). a 95% CI: 95% confidence interval of the odds ratio. b Includes reports of Medicare coverage, military coverage for veterans and dependents, or respondents who were otherwise classified as having any coverage besides private health insurance, Medicaid, or CHIP. * P < 0.05 (odds ratio that was statistically significant from the reference group). ** P < 0.01 (odds ratio that was statistically significant from the reference group). *** P < 0.001 (odds ratio that was statistically significant from the reference group).
with respect to key study variables. (Similar models also were run for past-year methamphetamine and non-methamphetamine misuse, but these data are not shown in Table 3.) Consistent with the unadjusted data, the covariate-adjusted estimates showed that persons under the age of 26 years were more likely than their older counterparts to be misusers of any stimulant; the same was found for Whites versus non-Whites. In addition, compared to the experience of older adults, youths and young adults had more than 10 times the odds of being pastyear users of the ADHD stimulants (but not other stimulants). Covariate-adjusted male–female relationships also were consistent with estimates based upon unadjusted data. In addition, males were more likely than females to be past-year methamphetamine misusers (OR = 1.41; P < 0.05). Persons in the lowest income category had higher odds of being misusers of any stimulant and ADHD stimulants relative to persons in the highest
income category. Any stimulant misuse was less likely among persons with health insurance but was more likely among persons in families receiving government assistance; these patterns did not hold in the ADHD-specific stimulant analyses. Misuse of any stimulant and of ADHD-specific stimulants did not differ significantly by population density when the models controlled for the potential confounding effects of other characteristics, such as race/ethnicity. Despite the large sample size for the 2002 public use file, it did not have sufficient numbers of respondents in the stimulant subgroups to estimate dependence or abuse among the following key subgroups of past-year misusers: non-methamphetamine misusers who were aged 26 or older, male, non-White or Hispanic, or living in nonmetropolitan areas; ADHD-only users who were aged 26 or older, non-White or Hispanic, or living in nonmetropolitan areas when the data were subset further
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Table 4 Dependence on or abuse of stimulants in the past year among past-year users, by stimulant category, age group, and gender: 2000 and 2001 Stimulant category/age group/gender
Percent (S.E.) Dependence or abuse
Dependence
Abuse
Any Total, 12 or older 12–17 18–25 26 or older Male, 12 or older Female, 12 or older
13.0 (1.40) 14.3 (1.43) 10.8 (1.22) 14.3 (3.20) 11.8 (2.01) 14.3 (1.92)
9.3 (1.31) 6.2 (0.96) 8.5 (1.10) 12.0 (3.06) 8.1 (1.92) 10.8 (1.75)
3.7 (0.55) 8.1 (1.09) 2.3 (0.58) 2.3 (1.07) 3.7 (0.75) 3.6 (0.79)
Non-METHb Total, 12 or older 12–17 18–25 26 or older Male, 12 or older Female, 12 or older
9.2(1.27) 10.8(1.51) 8.9(1.61) 8.0(3.22) 9.0(1.88) 9.4(1.78)
5.7(1.11) 3.4(0.83) 6.6(1.36) 6.8(3.02) 5.3(1.58) 6.0(1.62)
3.5 (0.66) 7.4 (1.30) 2.3 (0.87) 1.2 (1.20)c 3.6 (1.08) 3.4 (0.77)
2.3 (0.70) 2.2 (0.87) 3.1 (1.29) 0.1 (0.09)c 1.2 (0.63) 3.5 (1.34)
2.5 (0.72) 3.5 (1.21) 2.5 (1.16) 0.0 (0.00)c 3.5 (1.20) 1.2 (0.63)
STIMa
ADHD STIM onlyd Total, 12 or older 12–17 18–25 26 or older Male, 12 or older Female, 12 or older
4.7 (1.03) 5.7 (1.47) 5.6 (1.77) 0.1 (0.09)c 4.7 (1.35) 4.8 (1.49)
Denominators are past-year stimulant users; STIM: stimulant; Non-METH: non-methamphetamine; ADHD STIM: stimulant used to treat ADHD. Source: SAMHSA (2004c,d). a Estimates for nonmedical stimulant use in this table may differ slightly from published NSDUH estimates due to subsampling and reweighting of data for the public use file. b Used a stimulant nonmedically in the past 12 months but did not use methamphetamine in this period. c Low precision; use with caution. d Persons who were lifetime nonmedical users only of stimulants prescribed for ADHD and who used these stimulants nonmedically in the past year.
by demographics. Exploratory analyses of the larger combined 2000 and 2001 data showed patterns of misuse by age group, gender, race/ethnicity, and population density that were similar to those in the 2002 data. For example, an estimated 13% of recent nonmethamphetamine misusers aged 12–17 years in the 2002 data crossed survey-based DSM-IV thresholds for stimulant dependence or abuse but with an associated standard error (S.E.) of 2.5%; the corresponding estimate for the combined 2000 and 2001 data was 10.8% but with an S.E. of only 1.5%. Similarly, 8–9% of non-methamphetamine misusers aged 18–25 years in the 2002 data (S.E.: 1.7%) qualified as cases of survey-assessed dependence or abuse, compared with 8.9% (S.E.: 1.6%) in the combined 2000 and 2001 data. Among female non-methamphetamine misusers, 12% (S.E.: 3%) reported threshold numbers of dependence or abuse symptoms in 2002, compared with 9.4% in the combined 2000 and 2001 data (S.E.: 1.8%). Table 4 presents NSDUH-based estimates of dependence or abuse based on the combined 2000 and 2001 data. An estimated 13% of past-year misusers of any stimulant were classified as meeting criteria for stimulant dependence or abuse. This figure translates to an annual mean value of approximately 303,000 active cases of stimulant dependence or stimulant abuse in the population. About 10% of respondents aged 12–25 years who were past-year misusers of non-methamphetamine stimulants
(75,000 persons) qualified for DSM-IV stimulant dependence or had experienced one or more clinical features of abuse; persons classified as cases of abuse had fewer than three clinical features of dependence. More than half of these non-methamphetamine misusers (39,000) had experienced three or more clinical features of stimulant dependence. Clinical features of stimulant dependence predominated among adult stimulant misusers, and clinical features of abuse predominated among youth. Females who misused stimulants also had somewhat higher prevalences of the survey-assessed stimulant dependence syndrome, as compared with males, though the differences were modest and not statistically significant. Among females who misused ADHDspecific stimulants exclusively, an estimated 8000 had experienced three or more clinical features of DSM-IV stimulant dependence, and an estimated 3000 had experienced fewer than three clinical features of dependence but one or more clinical features of DSM-IV stimulant abuse. These values compare with only 3000 male ADHD-specific stimulant misusers having three or more clinical features of dependence and 10,000 who otherwise had experienced one or more clinical features of DSM-IV stimulant abuse. 4. Discussion Without minimizing concerns about a growing problem of methamphetamine misuse in the United States, our findings
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indicate that most recent stimulant misuse involves the diversion of prescription drugs. Some of the reported lifetime misuse involved newer extended-release stimulants, indicating that longer-acting stimulant formulations are not exempt from misuse. Moreover, most recent stimulant misusers aged 12–25 years exclusively misused prescription (i.e., non-methamphetamine) stimulants. Consistent with NSDUH data on any illegal drug use, pastyear stimulant misuse is more prevalent among persons aged 25 years or younger (SAMHSA, 2004a). This age relationship is even more dramatic among persons whose misuse was limited to ADHD stimulants. There also appear to be gender differences in misuse. Although males and females were equally likely to have used stimulants nonmedically (unlike the situation for any illegal drug use), males were more likely than females to have misused ADHD-specific stimulants. The relative prevalence of stimulant dependence or abuse in the combined 2000 and 2001 survey data also indicates some notable age and gender differences for the ADHD-specific stimulant group, with females somewhat more likely to meet criteria for dependence and males more likely to meet criteria for nondependent abuse. In addition to age and gender differences, some prevalences of misuse were lower in large metropolitan areas, compared with smaller metropolitan or rural areas. Further, rural stimulant misuse is not limited to methamphetamine. These findings run counter to the NSDUH pattern for any illegal drug use, which is less prevalent in rural areas (SAMHSA, 2004a). In comparison, McCabe et al. (2004) reported that 4.1% of a sample of 1536 public school students in grades 6–11 in a large Midwestern city were lifetime misusers of ADHD stimulants. Although their findings may not generalize to the national experience with ADHD stimulants, their finding that Black students were less likely than White students to be ADHD stimulant misusers was consistent with this study’s results from NSDUH. Nonetheless, both our findings and those of McCabe et al. indicate that the prevalence of ADHD stimulant misuse is not a trivial value from the public health perspective. These study data may have important policy and public health implications. First, misuse of these drugs can place increased demand on the health care system, which now faces additional requirements to treat the consequences of stimulant misuse. Many of the prescription stimulants that are assessed in the NSDUH are classified as Schedule II drugs, meaning that they have been judged to have a high potential for dependence or abuse when used outside of appropriate medical supervision. Consistent with this classification, 1 in 10 respondents aged 12–25 years who recently had misused only non-methamphetamine stimulants was identified as dependent on or an abuser of stimulants. Although the higher prevalence of dependence among females was not significantly different from the corresponding prevalence for males, the findings are not dissimilar from estimates provided via other research, showing an increased risk for dependence among females (Wu and Schlenger, 2003). Second, diverted medicines by definition do not benefit the patients who are intended to be using them. Thus, the health care system still faces the burden of responding to disorders that are undertreated or not treated at all.
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An additional concern is the potential for diversion when students take ADHD medications to school or are dosed during school hours. For example, students may sell medications to classmates or steal them from classmates or from the school. Approximately 8% of public middle and high schools reported at least one episode of diversion of these medications during the 2000–2001 school year, and most of these diversion episodes at school involved students selling or giving their medications to classmates (United States General Accounting Office, 2001). McCabe et al. (2004) reported that nearly one-fourth of the students in their sample who had been prescribed ADHD stimulants had been approached at least once to sell, trade, or give away their medications. Although it is tempting to make specific recommendations regarding policies for prescribing or using stimulants based on these data, it is important to remember that the current data address only the demand side of the drug diversion problem, not the supply side (e.g., how these drugs are being diverted). Specific recommendations for policy change would require more complete examination of both the supply and demand sides of the problem—i.e., more than these data can provide. Nevertheless, the current data indicate that the misuse of stimulants associated with the diversion of prescription medicines is substantial enough to merit follow-up work in this area. The concerns about diversion of prescription stimulants should not be construed as recommendations against the use of these medications to treat ADHD or other disorders under appropriate medical supervision. As noted previously, the benefits of these medications to treat ADHD are widely recognized, including benefits for treatment of ADHD in adults (Goldman et al., 1998; Faraone et al., 2004; Hechtman and Greenfield, 2003; Kociancic et al., 2004). Several recent studies have indicated no increased risk for substance experimentation or disorders among youth who were treated with stimulants for ADHD, or reduced risk relative to persons whose ADHD was not treated pharmacologically (Barkley et al., 2003; Fischer and Barkley, 2003; Biederman, 2003; Wilens et al., 2003). Such findings are not counter to the present findings because stimulant misusers in NSDUH were not asked about treatment for ADHD. Furthermore, Fischer and Barkley (2003) controlled for conduct disorder in their analyses. If youth with conduct disorder also are misusing prescription stimulants, they could be at increased risk for substance use disorders. An important strength of this study is that estimates are based on nationally representative data that reduce constraints upon inferences to be made about nonmedical stimulant use in the general U.S. population. Further, the survey methods provided a way for respondents to report sensitive behaviors confidentially and allowed respondents with limited reading ability to listen to the questions on headphones. As noted in Section 2, the computer-assisted design also improved data quality by reducing opportunities for respondents to give inconsistent answers (Kroutil and Handley, 2004). In addition, the large sample size in 2002 provided sufficient numbers of nonmedical stimulant users in the data to examine correlates of use, even when the data were further subdivided by demographic characteristics. Although the 2002 sample did not
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provide sufficient precision for examining stimulant dependence or abuse among subgroups of nonmedical users, the availability of common measures facilitated pooling of the data from 2000 and 2001. Limitations of the study include the cross-sectional design, which allows associations to be identified but constrains causal inferences, and reliance on respondent self-reports. The latter may result in underestimates or overestimates of prevalence, depending on circumstances and processes such as respondent recall and willingness to report nonmedical use. In particular, respondents with limited reading or spelling ability or low motivation to disclose substance use could underreport the misuse of “other” stimulants for which they had to type in the names (see Table 1). This study also shared the limitations inherent in any secondary analysis of data—namely, that the variables and measures in the data set were not developed with these analyses in mind. Specifically, measures for nonmedical use of most specific stimulants (e.g., methylphenidate) were limited to lifetime use. Although the NSDUH data permitted identification of subgroups such as persons who had not used methamphetamine in the past year or had used only ADHD stimulants, the data did not permit identification of persons who may have used more than one type of stimulant in the past year. Our findings highlight the magnitude of ADHD stimulant misuse in the United States and raise important new questions. Future research might examine, for example, the past-year use of specific stimulants other than methamphetamine (with or without use of methamphetamine in that same period), which would help differentiate between persons who use any available stimulant and those who have clear preferences for certain types of stimulants. In addition, information on how nonmedical users obtain stimulants would allow the relative importance of specific sources of diversion to be estimated and would be helpful in determining who bears the economic burden of misuse. Further research on motivations for misusing stimulants, such as expectations of weight control or improved academic performance, could be helpful in designing appropriate prevention programs. Longitudinal research on nonmedical use of prescription stimulants also would be important in identifying individual-level changes in patterns of use over time. For example, longitudinal evidence would help to clarify whether persons who start out using diverted prescription medications move toward using street drugs later in life. Acknowledgements Study design and data collection were done by the Substance Abuse and Mental Health Services Administration. The current analysis was sponsored by Eli Lilly and Company. References American Psychiatric Association, 1994. Diagnostic and Statistical Manual of Mental Disorders, 4th ed. American Psychiatric Association, Washington, DC. American Academy of Pediatrics, Subcommittee on AttentionDeficit/Hyperactivity Disorder, Committee on Quality Improvement, 2001. Clinical practice guideline: treatment of the school-aged child
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