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Adversity among drug users: relationship to impulsivity
Drug and Alcohol Dependence 78 (2005) 65–71
Adversity among drug users: relationship to impulsivity Jumi Hayaki, Michael D. Stein∗ , Joanna A. Lassor, Debra S. Herman, Bradley J. Anderson Brown Medical School, Division of General Internal Medicine, Rhode Island Hospital, 593 Eddy Street, Providence, RI 02903, USA Received 22 June 2004; received in revised form 17 September 2004; accepted 20 September 2004
Abstract Illicit substance users experience adverse life events, but few studies have examined the role of impulsivity in these events. The present investigation sought to establish a link between negative life experiences and a trait measure of impulsivity and demonstrate that this association remains even accounting for potential confounds. Participants were 330 heroin and cocaine users recruited from the community for a health service research study. Participants completed a structured interview that assessed topics including drug and alcohol use, impulsivity, and negative life events. This group of drug users reported high rates of adverse life events in the 6 months prior to the assessment. No specific substance abuse/dependence diagnosis or combination of diagnoses was associated with adversity. Number of substance-related diagnoses was associated with adverse life events, but not when adjusting for impulsivity. Experience of these events was significantly associated with impulsivity (p < .001), above and beyond the shared relation with demographic variables, substance abuse and dependence, and number of substance-related diagnoses. These findings document the high frequencies of recent adverse life events among illicit drug users and indicate that trait impulsivity is associated with increased risk of these life events. © 2004 Elsevier Ireland Ltd. All rights reserved. Keywords: Drug use; Adverse life events; Impulsivity
1. Introduction 1.1. Substance abusers and adverse life events Adversity is thought to characterize the lives of illicit drug users, but few recent studies have attempted to quantify negative life experiences in this population. Some of the adverse life events previously reported in the literature include a high rate of accidents and injuries, family problems, unemployment, criminal behavior, and legal consequences (O’Connor and Fiellin, 2000). Many of the studies that report the actual rates of these adverse life events among substance users were conducted decades ago (e.g., Dudley et al., 1976; Kosten et al., 1986; Prusoff et al., 1977) and omitted problems common in this population such as not having enough money to pay for food, living on the street or in a shelter, and drug overdoses. With only a few exceptions (e.g., O’Doherty, 1991; Regidor et al., 1996), the actual rates of these life events have not been ∗
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revisited after 1990. Although adversity is widely considered a risk factor for substance use and abuse initiation, maintenance, or relapse, recent studies have typically not assessed the actual prevalence of adverse life events among substance users. Indeed, it is generally presumed, but not systematically documented, that illicit drug users experience adverse life events at high frequency. Although a link between illicit drug use and adverse life events has been suggested, possible explanations for this association are not clear. It is possible that there is a direct relationship between the severity of substance use and the incidence of negative life experiences; that is, that the use of substances itself heightens the likelihood of adversity. Alternatively, it is possible that substance use develops or worsens in response to adversity, for instance, to self-medicate the psychological distress resulting from negative life events. Yet another possibility is that the association between substance abuse and adverse life events occurs in the context of other factors. One potential such factor is a personality characteristic known to be prominent among those who abuse substances, namely, impulsivity.
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1.2. Impulsivity and substance abuse Previous research has demonstrated an association between substance abuse and impulsivity. A number of studies using self-report instruments have found that substance abusers demonstrate higher levels of trait impulsivity than normal controls (for one review, see Moeller and Dougherty, 2002). Several studies have also shown that illicit drug users discount delayed rewards at higher rates than do controls (e.g., Kirby et al., 1999; Odum et al., 2000), and the rate of discounting appears to correlate positively with trait measures of impulsivity (Alessi and Petry, 2003; Kirby et al., 1999; Petry, 2001). Individuals with a history of drug dependence also report greater impulsivity than those with no such history (Allen et al., 1998). Among substance abusers, impulsivity appears to be associated with greater substance use severity: individuals who are dependent on multiple substances report greater trait impulsivity than those who are dependent on single substances (O’Boyle and Barratt, 1993). In addition, negative affect and impulsivity have been associated with earlier age of substance abuse onset, more substance-related negative consequences, and higher rates of substance abuse among relatives (Henderson et al., 1998). Impulsivity is thus considered a key aspect of substance abuse; this trait and its associated features have been recognized in many nosological systems for substance use disorders. For instance, impulsive and aggressive behavioral patterns are hallmark clinical features of Type A (Babor et al., 1992) and Type II (Cloninger, 1987) alcoholism. The DSMIV (American Psychiatric Association, 1994) diagnostic criteria for substance dependence also capture impulsive behavior (Evenden, 1999). 1.3. Definitions of impulsivity Impulsivity has been defined in two general ways: reward delay and rapid response (Swann et al., 2002). The concept of reward delay is based on an animal model of reward dependence in which the organism favors immediate reward, even if it is smaller (Ainslie, 1975; Monterosso and Ainslie, 1999). In human research, this subtype has been most extensively examined in delay discounting procedures. The concept of rapid response, also termed response inhibition or non-planning impulsivity, encompasses several aspects of present-focused behavior, including quick decision-making, inability to withhold action, and action without regard to consequences (Evenden, 1999; Lane et al., 2003; Moeller et al., 2001). Although both approaches have been implicated in substance abuse, some researchers have suggested that this second subtype of impulsivity is more strongly associated with psychopathology (Swann et al., 2002). It has also been argued that each dimension of impulsivity reflects a different aspect of substance abuse (e.g., Lane et al., 2003). For instance, the reward delay subtype of impulsivity may serve as an underlying vulnerability that may trigger substance abuse onset, whereas the rapid response subtype may contribute to
the maintenance of substance abuse among individuals who already use. Another possibility is that reward delay impulsivity is triggered during an individual’s active decision to use or abstain from substances, whereas rapid response impulsivity may be activated during more automatic substance use patterns such as cue-reactive behaviors. The present investigation focuses only on rapid response impulsivity, which may reflect the tendency to take risks and act on impulse without regard to consequence. This study sought to quantify the experience of adverse life events in a large sample of illicit drug users, to examine the association between these negative life experiences and trait impulsivity, and to determine whether this association is independent of the shared relation with potential confounds, including a measure of substance use severity.
2. Methods 2.1. Participant recruitment Between 1/24/02 and 1/24/04, participants were recruited for a health service research study of drug users. The study was advertised as a “quality of life” research project with a financial incentive at various community agencies, through newspaper advertisements, and on the street with flyers. Those interested were directed to call the study telephone number to be screened by study research assistants. During the recruitment period, the study telephone received 1390 calls. If eligible after a telephone screening, individuals were invited to the research site at Rhode Island Hospital, Providence, for a more detailed assessment. Inclusion criteria assessed on the telephone included the following: (1) age between 18 and 70 years; (2) heroin or cocaine injection during the preceding 30 days or non-injection heroin or cocaine use at least weekly for the past 6 months; (3) fewer than 30 of the last 90 days spent in institutional settings including prison, residential drug treatment or hospitalization; (4) ability to speak English; (5) denial of intent to harm self or others; and (6) absence of psychosis (commonly seen in our study population). Of the 524 individuals who were eligible for the study based on the telephone screen, 344 scheduled and kept appointments. At this appointment, eligibility was confirmed by reviewing the drug use frequency questions and administering the SCID to determine the possibility of psychosis. Based on these confirmatory questions, 14 individuals were deemed ineligible for the study, leaving a final sample of 330. The final sample provided written consent for the study, which had been approved by the Rhode Island Hospital/Lifespan Institutional Review Board. Participants were then administered a 90-min structured interview that included sections on demographics, mood, drug and alcohol use, impulsivity, and adverse life events. Individuals participating in the interview received compensation of $20.
J. Hayaki et al. / Drug and Alcohol Dependence 78 (2005) 65–71 Table 1 Adverse life events in the 6 months prior to interview (n = 330) Questionnaire item
Yes% (n)
Has there been a time when you did not have enough money to pay for the things you needed to live, like food? Did you and your spouse/partner/lover break up? Have you been in a major physical fight (for example, involving kicking, hitting, choking, shooting, stabbing, burning, pushing, or threatening with a weapon)? Have you been sexually assaulted (for example, unwanted sexual touching anywhere on your body, touching of genitals and/or breasts, or made to have oral sex or vaginal or anal intercourse against your will by force or threat of force)? Have your children been taken away from you? Have you spent time in prison? Have you spent time on the street or in a shelter? Had someone close to you (friend or relative) died? Have you been fired or laid off from a job? Have you had a major conflict with a friend or family member that caused serious or permanent harm to the relationship? Have you been arrested? Have you contracted a sexually transmitted disease (such as gonorrhea, clap, syphilis, chlamydia, herpes)? Have you had a major accident (outside of a physical fight), such as a motor vehicle accident, gunshot, stab wound, broken or dislocated bone or joint, transportation accident, or other accident requiring medical attention? Have you had a drug overdose?
72.1 (240)
37.0 (122) 31.2 (103)
3.9 (13)
5.3 (17) 22.7 (75) 47.9 (158) 37.6 (124) 21.2 (70) 38.8 (128)
25.5 (84) 3.3 (11)
8.8 (29)
10.6 (35)
2.2. Measures 2.2.1. Demographic characteristics The following demographic variables were utilized: age in years, gender, and racial or ethnic group. 2.2.2. Adverse life events Adverse life events were assessed using a 14-item checklist derived from the Social Readjustment Rating Scale (Holmes and Rahe, 1967). Adaptations of this instrument have been utilized in previous research on life events among substance users (e.g., Kosten et al., 1986). In this study, participants were given the following instructions: “Below is a list of events that have happened to some people in this study. Please indicate which events, if any, have happened to you in the past 6 months.” Sample items include job loss, major accident, major relationship conflict, and time in prison; a complete list of items can be found in Table 1. Participants endorsed events that had occurred in the past 6 months; the total number of items endorsed then served as the composite scale index.
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2.2.3. Impulsivity The Impulsiveness subscale of the Eysenck I7 Questionnaire (Eysenck et al., 1985) was used to measure this personality characteristic. The I7 Impulsiveness subscale consists of 19 dichotomous items (of which three are reverse-scored) that assess behaviors reflecting a general tendency toward lack of planning, quick decision-making, and impulsive action. The subscale score is calculated by summing the affirmative responses, with higher scores indicating greater impulsivity. The Impulsiveness subscale has generally demonstrated good internal consistency reliability, with Cronbach’s alpha coefficients ranging from .55 in one report (Luengo et al., 1991) to .83 or .84 in other studies (e.g., Eysenck et al., 1985; Corulla, 1987). In this sample, the subscale demonstrated good internal consistency, as indicated by a Cronbach’s alpha coefficient (.84) of similar magnitude. 2.2.4. Substance use severity Substance use severity was defined in two ways. (1) First, substance use severity was operationalized as the number of current DSM-IV substance abuse or dependence diagnoses in the following four categories: alcohol, opioids, cannabis, and cocaine. Diagnoses were determined using the alcohol and drug abuse/dependence module of the Structured Clinical Interview for DSM-IV Patient Version (SCID-P; First et al., 1997). These particular drug classes were selected because they represent the most commonly used and abused substances in the community from which this sample was drawn. (2) Substance use severity was also measured using the fifth edition of the Addiction Severity Index (ASI; McLellan et al., 1992). The ASI is a widely used structured clinical interview that assesses substance use/abuse and psychosocial functioning in a variety of domains including medical, employment, legal, family/social, and psychiatric. For the purpose of the present investigation, the drug composite index was utilized as a measure of substance use severity. The psychometric properties of the drug composite index have been demonstrated in previous research. 2.3. Analyses For each of the 14 adverse life events, we report the mean impulsivity score of those who experienced the event and those who did not. We used t-tests to test for differences in mean impulsivity scores. We also report Cohen’s standardized effect coefficient (d ) as an indicator of the relative magnitude of association between impulsivity and each adverse life event. The adverse life events composite index was technically a count variable with possible scores ranging from 0 to 14. However, the observed distribution was unimodal and exhibited only moderate positive skewness. Exploratory analysis using the ladder and gladder procedures in Stata 8.2 (StatCorp, 2003) indicated that a square-root transformation generated an approximately normal response variable. Analyses using the transformed and untransformed response
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Table 2 Impulsivity and the experience of adverse life events Experienced life event
Too little money for needs Spouse/partner/lover break up Major physical fight Sexually assaulted Have children taken away Spent time in prison Time on street or in shelter Death of close friend/relative Fired or laid off job Major conflict friend/family Been arrested Contracted a STD Major accident Drug overdose
No
Yes
d
t (p)
10.11 (±4.78) 11.17 (±4.63) 11.12 (±4.50) 11.62 (±4.56) 11.46 (±4.58) 11.11 (±4.67) 10.89 (±4.61) 11.49 (±4.48) 11.31 (±4.59) 10.76 (±4.72) 11.16 (±4.67) 11.53 (±4.62) 11.42 (±4.64) 11.39 (±4.60)
12.13 (±4.42) 12.22 (±4.49) 12.57 (±4.67) 10.54 (±5.59) 14.00 (±4.44) 13.16 (±3.97) 12.32 (±4.48) 11.72 (±4.81) 12.54 (±4.52) 12.86 (±4.10) 12.76 (±4.22) 12.45 (±4.08) 13.17 (±3.87) 13.11 (±4.40)
.44 .23 .32 −.23 .55 .45 .31 .05 .27 .46 .34 .20 .38 .37
3.61 (<.001) 2.02 (.044) 2.68 (.008) −.83 (.408) 2.23 (.026) 3.45 (.001) 2.86 (.005) .44 (.664) 1.99 (.047) 4.13 (<.001) 2.77 (.006) .65 (.515) 1.97 (.050) 2.10 (.036)
variable yielded statistically consistent results. To simplify the presentation, we report results using the untransformed index of adverse life events as the response variable. OLS regression effects were estimated. Because analysis of residuals exhibited some heteroskedasticity, we used robust standard error estimates to calculate tests of statistical significance (StatCorp, 2003). The response variable and continuous predictor variables (age and impulsivity) were standardized to zero mean and unit variance prior to estimation. The effects for categorical predictor variables are y-standardized (Long, 1997), whereas the effects associated with continuous predictors are fully standardized. In bivariate analyses, we separately tested the effects of each of four current substance abuse/dependence diagnoses (alcohol, opioid, cocaine, and cannabis). Readers should note that in this cohort we are generally not comparing those with a specific diagnosis to those with no substance-related diagnosis. Indeed, only 28 (8.5%) participants did not meet diagnostic criteria for current abuse/dependence criteria for any of these four substances, and only 10.6% did not meet diagnostic criteria for current opioid or cocaine abuse/dependence. Just over 53.3% met criteria for current abuse/dependence on at least two different substances (30.0% for both opioid and cocaine). Therefore, we constructed a count variable indicating the number of current abuse/dependence diagnoses to determine if those with multiple diagnoses were more likely to experience adverse life events. Though not presented in tabular form, we also tested the first-order interaction for all pairs of substance-related diagnoses (e.g., opioid by alcohol, opioid by cocaine) to determine if specific combinations of substance-related disorders were especially likely to be associated with adverse life events.
3. Results A majority of the 330 participants were male (62.1%), just over half (54.6%) were Caucasian, and they aver-
aged 38.92 (±9.23) years of age. Participants reported using heroin and/or cocaine for an average of 18.19 (S.D. = 9.16) years. Among heroin users, the average age of initiating heroin use was 24.83 (S.D. = 8.35) years; among cocaine users, the average age of initiating cocaine use was 22.11 (S.D. = 8.02) years. The mean ASI drug composite score was 0.267 (S.D. = 0.132). With respect to SCID diagnoses, 96 participants (29.1%) met criteria for current alcohol abuse/dependence, 183 (55.5%) for current opioid abuse/dependence, 76 (23.0%) for current cannabis abuse/dependence, and 211 (63.9%) for current cocaine abuse/dependence. Over half the sample (176 individuals, or 53.3%) met criteria for more than one substance abuse/dependence diagnosis. Thirty-five individuals (10.6%) did not meet criteria for current cocaine or opioid abuse/dependence. Only five individuals (1.5%) did not meet criteria for lifetime cocaine or opioid abuse/dependence. Observed impulsivity scores ranged from 0 to 19 (the theoretical minimum and maximum scale scores) and averaged 11.56 (±4.60). These individuals experienced considerable exposure to adverse life events in the prior 6 months (Table 1). The observed range of scores on the adverse life events index was 0–13 (a score of 14 was the highest possible value). On average, participants reported 3.66 (±2.37) adverse life events. Only 6.1% of the sample reported experiencing none of the listed adverse life events during this assessment period. Impulsivity was associated significantly with 11 of the 14 adverse life events (Table 2). Higher mean impulsivity was significantly associated with having too little money to meet needs, breaking up with a spouse, partner, or lover, being in a major physical fight, having children taken away, spending time in prison, spending time on the street or in a shelter, being fired or laid off from a job, having a major conflict with friend or family member, being arrested, having a major accident, and having a drug overdose in the last 6 months. Impulsivity was not significantly associated with being sexually assaulted, experiencing the death of a close friend or
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Table 3 Unadjusted and adjusted effects of selected predictor variables on the expected number of adverse life events Unadjusted effects
Age Gender (male) Ethnicity (caucasian) Alcohol abuse/dependence Opioid abuse/dependence Cannabis abuse/dependence Cocaine abuse/dependence #Abuse/dependence diagnosis Impulsivity
Adjusted effects
ba
(p)b
t
−.123 −.000 .139 .237 .174 .249 .111 .160 .289
−2.28 (.023) −.00 (.998) 1.26 (.210) 1.88 (.062) 1.57 (.118) 1.85 (.065) .95 (.341) 2.64 (.009) 5.22 (.000)
ba
t (p)b
−.006 −.020 .106
−1.11(.267) .18(.853) .99(.324)
.094 .254
1.71(.088) 4.62(.000) R2 = .10
a b
Effects for continuous variables age and impulsivity are fully standardized. Effects for dichotomous predictors are y-standardized (see Long, 1997). Reported test statistics are based on robust standard errors. Model-based standard errors were of similar magnitude and gave consistent results.
relative, or contracting a sexually transmitted disease (STD) (Table 2). Table 3 presents the unadjusted and adjusted effects of selected predictors on the index of adverse life effects. Bivariate analysis indicated a significant inverse association between age and adverse life events; however, this association was sharply attenuated and not statistically significant when adjusted for other covariates included in the full model. The number of reported adverse life events was not significantly associated with other background characteristics such as gender or race. The gender by impulsivity interaction did not contribute significantly to the model and is therefore not presented here. None of the current substance (alcohol, opioid, cannabis, cocaine) abuse/dependence diagnoses were significantly associated with the index of adverse life events at the conventionally accepted p < .05 level (Table 3). The association between number of abuse/dependence diagnoses and adverse life events was substantively attenuated and became non-significant when adjusted for impulsivity. Finally, adverse life events were positively associated with impulsivity, both in bivariate analyses and in the final model. In addition, this model was repeated with the ASI drug composite index as the measure of substance use severity (rather than the individual SCID diagnoses and number of SCID diagnoses) and yielded virtually identical results. To determine whether specific combinations of substancerelated disorders were especially likely to be associated with higher rates of adverse life events, we tested the first-order interaction between the six possible pairs of specific disorders. Probability values for these tests ranged from .301 for the first-order cocaine abuse/dependence by cannabis abuse/dependence to .841 for the first-order cocaine by alcohol interaction effect. These data provided no evidence that specific combinations of drug disorders are more likely associated with especially high rates of adverse life events. Finally, we ran additional analyses specifically to explore the pattern of association among number of abuse/ dependence diagnoses, adverse life events, and impulsivity. Impulsivity and number of substance-related diagnoses were
significantly associated in the bivariate analysis (r = .237, p = .000). The association between the number of current substance-related disorders and adverse life events was statistically significant when adjusted for age, gender, and ethnicity (b = .150, t = 2.45, p = .015). However, when impulsivity was included in the model, the effect of number of substancerelated diagnoses weakened and was no longer statistically significant, as described above (Table 3).
4. Discussion The participants in this study reported a high frequency of adverse life events in the 6 months prior to the interview. This finding is consistent with previous reports that substance abusers experience heightened adversity (e.g., Kosten et al., 1986). What is especially remarkable is that only 6.1% of all participants reported no adverse life events in the past 6 months, suggesting that disturbingly event-filled lives were the norm in this sample of substance users. What cannot be addressed here is whether these experiences predispose substance users to use drugs more frequently, or whether they are actual consequences of the substance use itself. Results also indicate that impulsivity was able to distinguish between individuals who did or did not endorse all but three of the 14 adverse life events. Exceptions were sexual assault, death of a close friend or relative, and contracting a sexually transmitted disease. In the case of sexual assault and STDs, it is possible that the association with impulsivity was non-significant due to the low endorsement rate for these events. It is also possible that one’s trait impulsivity would not necessarily impact an outcome such as death of a close friend or relative that is beyond one’s behavioral control. For each of the 11 remaining items, those who endorsed the item scored significantly higher on the impulsivity measure. This finding supports the notion that impulsive individuals are more likely to behave in ways that put them at risk for negative life events. Of course, a causal relationship cannot be inferred from these cross-sectional findings. However, given that a trait measure
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of impulsivity was used, whereas adverse life events were assessed only in the previous 6 months, it is likely that impulsive tendencies predated the occurrence of the negative life events. Indeed, impulsivity was operationalized in terms of behaviors reflecting a general tendency to act quickly without plan or regard to consequence. As such, the assessment of impulsivity was not temporally bound, but rather reflected an overall, presumably somewhat stable, characteristic of the individual. In contrast, the assessment of adverse life events was temporally limited to the past 6 months, suggesting a more recent timeframe. In this sample, no single substance-related abuse/dependence diagnosis was significantly associated with adverse life events in bivariate analyses. However, as noted previously, this was a drug-using sample, almost all of who met criteria for at least one substance abuse/dependence diagnosis. Therefore, although these bivariate associations trended in the expected direction, for each individual substance, drug users meeting diagnostic criteria were essentially compared to other drug users meeting diagnostic criteria for at least one other substance, as opposed to a non-substance using control group. Given our sample selection, in order to examine whether specific combinations of diagnoses were associated with greater adversity, first-order interactions among the possible pairs of substance diagnoses were also tested. These subsequent analyses demonstrated that no specific combination of substance-related diagnoses was associated with greater adversity, suggesting that, among substance users, the likelihood of adverse life events is not linked to any specific pattern of substance abuse. That the number of substancerelated diagnoses was associated with adverse life events in bivariate analyses indicates that it is perhaps the severity of substance abuse, rather than the specific substance or substances used, that increases the likelihood of adverse life events. This study has the following limitations. First, substance use severity was primarily defined as the number of current DSM-IV (APA, 1994) alcohol/substance abuse or dependence diagnoses for four drug classes that are commonly used and/or abused in this population. This categorical approach does not capture non-diagnostic substance use that may otherwise have impacted results. (However, it should be noted that the statistical model was also tested using the drug composite index of the ASI, with virtually identical findings.) Of related concern, the study utilized exclusively self-report instruments. The use of self-report measures is common in previous research on impulsivity (e.g., Allen et al., 1998). Nonetheless, the frequencies of adverse life events were extremely high for many items considering the 6-month timeframe of the assessment. It is possible that participants either misremembered or misrepresented the adversity in their lives or responded to the probes with a different timeframe than that stated in the instructions. Another possibility is that the amount of adversity in this sample was higher than in other groups of substance users. For instance, the use of a monetary incentive for participation may have preferentially
drawn those substance users with worse life circumstances. A different sample of drug users may have provided different absolute values of adverse events, and the added presence of a non-substance using comparison group could have provided another context in which to interpret the reported frequencies. A final limitation of the present study was the use of a unidimensional definition of impulsivity. Although the impulsivity subscale of the Eysenck I7 Questionnaire is a widely used measure of trait impulsivity that has performed well in other samples of substance abusers (e.g., Alessi and Petry, 2003), it nonetheless represents only one aspect of impulsivity. The fact that this particular subtype of impulsivity uniquely predicted the experience of adverse life events suggests that it was an appropriate choice for the questions addressed here. However, it is also possible that alternative dimensions of impulsivity may also carry predictive power, especially if each dimension explains a different aspect of substance abuse, as has been suggested previously (Lane et al., 2003). Trait impulsivity may develop early in life, triggering the onset of substance use or the occurrence of adverse life events. For instance, the tendency to take risks and act without regard to consequence may manifest in poor behavioral choices and heighten the likelihood of using and abusing substances or experiencing adverse life events. However, recent evidence shows that the excessive use of certain substances causes neurological deficits associated with impulsivity (e.g., Morgan, 1998). Therefore, it is possible that problematic substance use elicits impulsive behavior, which then leads to adversity. It is also possible that experiencing adverse life events may exacerbate impulsive tendencies or serve as a precursor to substance use. To determine temporal sequence, these models require prospective measurement. This study has quantified recent adverse life events in a large sample of illicit drug users. In addition, results demonstrated a unique association between these adverse life events and a measure of trait impulsivity that is above and beyond the shared relation with demographic variables, substance abuse and dependence, and number of substance-related diagnoses. Of particular interest, the association between number of abuse/dependence diagnoses and adverse life events was attenuated and not statistically significant when adjusted for impulsivity. Although these data were not sufficient to determine temporal ordering, the pattern of results was consistent with an explanation in which impulsivity partially mediates the association between number of substance-related disorders and adverse life events. A second plausible explanation is that impulsivity is a relatively enduring trait that at least partially accounts for the association between number of substance-related disorders and number of adverse life events. Longitudinal data are needed to disentangle the temporal order. These findings therefore lend non-temporal support to the notion that impulsivity is a risk factor for the experience of adverse life events and has implications for targeting clinical intervention. Future studies should replicate these findings in other groups of illicit drug users using longitudinal study designs.
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Acknowledgments This study was funded by the National Institutes of Health Grants #MH62719 and DA13759. Dr. Stein is a recipient of a Mid-Career Investigator Award from the National Institute on Drug Abuse (K24 DA00512). We are grateful to two anonymous reviewers for their helpful comments and suggestions. Finally, we acknowledge Peter Friedmann and Susan Ramsey for comments on earlier drafts.
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Kosten, T.R., Rounsaville, B.J., Kleber, H.D., 1986. A 2.5-year follow-up of depression, life crises, and treatment effects on abstinence among opioid addicts. Arch. Gen. Psychiat. 43, 733–738. Lane, S.D., Cherek, D.R., Rhoades, H.M., Pietras, C.J., Tcheremissine, O.V., 2003. Relationships among laboratory and psychometric measures of impulsivity: implications in substance abuse and dependence. Addict. Disord. Their Treatment 2, 33–40. Long, S.J., 1997. Regression Models For Categorical and Limited Dependent Variables. Sage, Thousand Oaks, CA. Luengo, M.A., Carrillo-de-la-Pe˜na, M.T., Otero, J.M., 1991. The components of impulsiveness: a comparison of the I.7 Impulsive Questionnaire and the Barratt Impulsiveness Scale. Pers. Indiv. Differ. 12, 657–667. McLellan, A.T., Kushner, H., Metzger, D., Peters, R., Smith, I., Grisson, G., Pettinati, H., Argeriou, M.H., 1992. The fifth edition of the Addiction Severity Index. J. Subst. Abuse Treat. 9, 199–213. Moeller, F.G., Barratt, E.S., Dougherty, D.M., Schmitz, J.M., Schwann, A.C., 2001. Psychiatric aspects of impulsivity. Am. J. Psychiat. 158, 1783–1793. Moeller, F.G., Dougherty, D.M., 2002. Impulsivity and substance abuse: what is the connection? Addict. Disord. Their Treatment 1, 3– 10. Monterosso, J., Ainslie, G., 1999. Beyond discounting: possible experimental models of impulse control. Psychopharmacology 146, 339–347. Morgan, M.J., 1998. Recreational use of “ecstasy” (MDMA) is associated with elevated impulsivity. Neuropsychopharmacology 19, 252– 264. O’Boyle, M., Barratt, E.S., 1993. Impulsivity and DSM-III-R personality disorders. Pers. Indiv. Differ. 14, 609–611. O’Connor, P.G., Fiellin, D.A., 2000. Pharmacologic treatment of heroindependent patients. Arch. Int. Med. 133, 40–54. O’Doherty, F., 1991. Is drug use a response to stress? Drug Alcohol Depend. 29, 97–106. Odum, A.L., Madden, G.J., Badger, G.J., Bickel, W.K., 2000. Needle sharing in opioid-dependent outpatients: psychological processes underlying risk. Drug Alcohol Depend. 60, 259–266. Petry, N.M., 2001. Pathological gamblers, with and without substance use disorders, discount delayed rewards at high rates. J. Abnorm. Psychol. 110, 482–487. Prusoff, B., Thompson, W.D., Sholomskas, D., Riordan, C., 1977. Psychosocial stressors and depression among former heroin-dependent patients maintained on methadone. J. Nerv. Ment. Dis. 165, 57– 63. Regidor, E., Barrio, G., De la Fuente, L., Rodr´ıguez, C., 1996. Non-fatal injuries and the use of psychoactive drugs among young adults in Spain. Drug Alcohol Depend. 40, 249–259. StatCorp, 2003. Statistical Software: Release 8.0. College Station, Stata Corporation, TX. Swann, A.C., Bjork, J.M., Moeller, F.G., Dougherty, D.M., 2002. Two models of impulsivity: relationship to personality traits and psychopathology. Biol. Psychiat. 51, 988–994.
Adversity among drug users: relationship to impulsivity Jumi Hayaki, Michael D. Stein∗ , Joanna A. Lassor, Debra S. Herman, Bradley J. Anderson Brown Medical School, Division of General Internal Medicine, Rhode Island Hospital, 593 Eddy Street, Providence, RI 02903, USA Received 22 June 2004; received in revised form 17 September 2004; accepted 20 September 2004
Abstract Illicit substance users experience adverse life events, but few studies have examined the role of impulsivity in these events. The present investigation sought to establish a link between negative life experiences and a trait measure of impulsivity and demonstrate that this association remains even accounting for potential confounds. Participants were 330 heroin and cocaine users recruited from the community for a health service research study. Participants completed a structured interview that assessed topics including drug and alcohol use, impulsivity, and negative life events. This group of drug users reported high rates of adverse life events in the 6 months prior to the assessment. No specific substance abuse/dependence diagnosis or combination of diagnoses was associated with adversity. Number of substance-related diagnoses was associated with adverse life events, but not when adjusting for impulsivity. Experience of these events was significantly associated with impulsivity (p < .001), above and beyond the shared relation with demographic variables, substance abuse and dependence, and number of substance-related diagnoses. These findings document the high frequencies of recent adverse life events among illicit drug users and indicate that trait impulsivity is associated with increased risk of these life events. © 2004 Elsevier Ireland Ltd. All rights reserved. Keywords: Drug use; Adverse life events; Impulsivity
1. Introduction 1.1. Substance abusers and adverse life events Adversity is thought to characterize the lives of illicit drug users, but few recent studies have attempted to quantify negative life experiences in this population. Some of the adverse life events previously reported in the literature include a high rate of accidents and injuries, family problems, unemployment, criminal behavior, and legal consequences (O’Connor and Fiellin, 2000). Many of the studies that report the actual rates of these adverse life events among substance users were conducted decades ago (e.g., Dudley et al., 1976; Kosten et al., 1986; Prusoff et al., 1977) and omitted problems common in this population such as not having enough money to pay for food, living on the street or in a shelter, and drug overdoses. With only a few exceptions (e.g., O’Doherty, 1991; Regidor et al., 1996), the actual rates of these life events have not been ∗
Corresponding author. Tel.: +1 401 444 3830; fax: +1 401 444 5040. E-mail address: [email protected] (M.D. Stein).
0376-8716/$ – see front matter © 2004 Elsevier Ireland Ltd. All rights reserved. doi:10.1016/j.drugalcdep.2004.09.002
revisited after 1990. Although adversity is widely considered a risk factor for substance use and abuse initiation, maintenance, or relapse, recent studies have typically not assessed the actual prevalence of adverse life events among substance users. Indeed, it is generally presumed, but not systematically documented, that illicit drug users experience adverse life events at high frequency. Although a link between illicit drug use and adverse life events has been suggested, possible explanations for this association are not clear. It is possible that there is a direct relationship between the severity of substance use and the incidence of negative life experiences; that is, that the use of substances itself heightens the likelihood of adversity. Alternatively, it is possible that substance use develops or worsens in response to adversity, for instance, to self-medicate the psychological distress resulting from negative life events. Yet another possibility is that the association between substance abuse and adverse life events occurs in the context of other factors. One potential such factor is a personality characteristic known to be prominent among those who abuse substances, namely, impulsivity.
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1.2. Impulsivity and substance abuse Previous research has demonstrated an association between substance abuse and impulsivity. A number of studies using self-report instruments have found that substance abusers demonstrate higher levels of trait impulsivity than normal controls (for one review, see Moeller and Dougherty, 2002). Several studies have also shown that illicit drug users discount delayed rewards at higher rates than do controls (e.g., Kirby et al., 1999; Odum et al., 2000), and the rate of discounting appears to correlate positively with trait measures of impulsivity (Alessi and Petry, 2003; Kirby et al., 1999; Petry, 2001). Individuals with a history of drug dependence also report greater impulsivity than those with no such history (Allen et al., 1998). Among substance abusers, impulsivity appears to be associated with greater substance use severity: individuals who are dependent on multiple substances report greater trait impulsivity than those who are dependent on single substances (O’Boyle and Barratt, 1993). In addition, negative affect and impulsivity have been associated with earlier age of substance abuse onset, more substance-related negative consequences, and higher rates of substance abuse among relatives (Henderson et al., 1998). Impulsivity is thus considered a key aspect of substance abuse; this trait and its associated features have been recognized in many nosological systems for substance use disorders. For instance, impulsive and aggressive behavioral patterns are hallmark clinical features of Type A (Babor et al., 1992) and Type II (Cloninger, 1987) alcoholism. The DSMIV (American Psychiatric Association, 1994) diagnostic criteria for substance dependence also capture impulsive behavior (Evenden, 1999). 1.3. Definitions of impulsivity Impulsivity has been defined in two general ways: reward delay and rapid response (Swann et al., 2002). The concept of reward delay is based on an animal model of reward dependence in which the organism favors immediate reward, even if it is smaller (Ainslie, 1975; Monterosso and Ainslie, 1999). In human research, this subtype has been most extensively examined in delay discounting procedures. The concept of rapid response, also termed response inhibition or non-planning impulsivity, encompasses several aspects of present-focused behavior, including quick decision-making, inability to withhold action, and action without regard to consequences (Evenden, 1999; Lane et al., 2003; Moeller et al., 2001). Although both approaches have been implicated in substance abuse, some researchers have suggested that this second subtype of impulsivity is more strongly associated with psychopathology (Swann et al., 2002). It has also been argued that each dimension of impulsivity reflects a different aspect of substance abuse (e.g., Lane et al., 2003). For instance, the reward delay subtype of impulsivity may serve as an underlying vulnerability that may trigger substance abuse onset, whereas the rapid response subtype may contribute to
the maintenance of substance abuse among individuals who already use. Another possibility is that reward delay impulsivity is triggered during an individual’s active decision to use or abstain from substances, whereas rapid response impulsivity may be activated during more automatic substance use patterns such as cue-reactive behaviors. The present investigation focuses only on rapid response impulsivity, which may reflect the tendency to take risks and act on impulse without regard to consequence. This study sought to quantify the experience of adverse life events in a large sample of illicit drug users, to examine the association between these negative life experiences and trait impulsivity, and to determine whether this association is independent of the shared relation with potential confounds, including a measure of substance use severity.
2. Methods 2.1. Participant recruitment Between 1/24/02 and 1/24/04, participants were recruited for a health service research study of drug users. The study was advertised as a “quality of life” research project with a financial incentive at various community agencies, through newspaper advertisements, and on the street with flyers. Those interested were directed to call the study telephone number to be screened by study research assistants. During the recruitment period, the study telephone received 1390 calls. If eligible after a telephone screening, individuals were invited to the research site at Rhode Island Hospital, Providence, for a more detailed assessment. Inclusion criteria assessed on the telephone included the following: (1) age between 18 and 70 years; (2) heroin or cocaine injection during the preceding 30 days or non-injection heroin or cocaine use at least weekly for the past 6 months; (3) fewer than 30 of the last 90 days spent in institutional settings including prison, residential drug treatment or hospitalization; (4) ability to speak English; (5) denial of intent to harm self or others; and (6) absence of psychosis (commonly seen in our study population). Of the 524 individuals who were eligible for the study based on the telephone screen, 344 scheduled and kept appointments. At this appointment, eligibility was confirmed by reviewing the drug use frequency questions and administering the SCID to determine the possibility of psychosis. Based on these confirmatory questions, 14 individuals were deemed ineligible for the study, leaving a final sample of 330. The final sample provided written consent for the study, which had been approved by the Rhode Island Hospital/Lifespan Institutional Review Board. Participants were then administered a 90-min structured interview that included sections on demographics, mood, drug and alcohol use, impulsivity, and adverse life events. Individuals participating in the interview received compensation of $20.
J. Hayaki et al. / Drug and Alcohol Dependence 78 (2005) 65–71 Table 1 Adverse life events in the 6 months prior to interview (n = 330) Questionnaire item
Yes% (n)
Has there been a time when you did not have enough money to pay for the things you needed to live, like food? Did you and your spouse/partner/lover break up? Have you been in a major physical fight (for example, involving kicking, hitting, choking, shooting, stabbing, burning, pushing, or threatening with a weapon)? Have you been sexually assaulted (for example, unwanted sexual touching anywhere on your body, touching of genitals and/or breasts, or made to have oral sex or vaginal or anal intercourse against your will by force or threat of force)? Have your children been taken away from you? Have you spent time in prison? Have you spent time on the street or in a shelter? Had someone close to you (friend or relative) died? Have you been fired or laid off from a job? Have you had a major conflict with a friend or family member that caused serious or permanent harm to the relationship? Have you been arrested? Have you contracted a sexually transmitted disease (such as gonorrhea, clap, syphilis, chlamydia, herpes)? Have you had a major accident (outside of a physical fight), such as a motor vehicle accident, gunshot, stab wound, broken or dislocated bone or joint, transportation accident, or other accident requiring medical attention? Have you had a drug overdose?
72.1 (240)
37.0 (122) 31.2 (103)
3.9 (13)
5.3 (17) 22.7 (75) 47.9 (158) 37.6 (124) 21.2 (70) 38.8 (128)
25.5 (84) 3.3 (11)
8.8 (29)
10.6 (35)
2.2. Measures 2.2.1. Demographic characteristics The following demographic variables were utilized: age in years, gender, and racial or ethnic group. 2.2.2. Adverse life events Adverse life events were assessed using a 14-item checklist derived from the Social Readjustment Rating Scale (Holmes and Rahe, 1967). Adaptations of this instrument have been utilized in previous research on life events among substance users (e.g., Kosten et al., 1986). In this study, participants were given the following instructions: “Below is a list of events that have happened to some people in this study. Please indicate which events, if any, have happened to you in the past 6 months.” Sample items include job loss, major accident, major relationship conflict, and time in prison; a complete list of items can be found in Table 1. Participants endorsed events that had occurred in the past 6 months; the total number of items endorsed then served as the composite scale index.
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2.2.3. Impulsivity The Impulsiveness subscale of the Eysenck I7 Questionnaire (Eysenck et al., 1985) was used to measure this personality characteristic. The I7 Impulsiveness subscale consists of 19 dichotomous items (of which three are reverse-scored) that assess behaviors reflecting a general tendency toward lack of planning, quick decision-making, and impulsive action. The subscale score is calculated by summing the affirmative responses, with higher scores indicating greater impulsivity. The Impulsiveness subscale has generally demonstrated good internal consistency reliability, with Cronbach’s alpha coefficients ranging from .55 in one report (Luengo et al., 1991) to .83 or .84 in other studies (e.g., Eysenck et al., 1985; Corulla, 1987). In this sample, the subscale demonstrated good internal consistency, as indicated by a Cronbach’s alpha coefficient (.84) of similar magnitude. 2.2.4. Substance use severity Substance use severity was defined in two ways. (1) First, substance use severity was operationalized as the number of current DSM-IV substance abuse or dependence diagnoses in the following four categories: alcohol, opioids, cannabis, and cocaine. Diagnoses were determined using the alcohol and drug abuse/dependence module of the Structured Clinical Interview for DSM-IV Patient Version (SCID-P; First et al., 1997). These particular drug classes were selected because they represent the most commonly used and abused substances in the community from which this sample was drawn. (2) Substance use severity was also measured using the fifth edition of the Addiction Severity Index (ASI; McLellan et al., 1992). The ASI is a widely used structured clinical interview that assesses substance use/abuse and psychosocial functioning in a variety of domains including medical, employment, legal, family/social, and psychiatric. For the purpose of the present investigation, the drug composite index was utilized as a measure of substance use severity. The psychometric properties of the drug composite index have been demonstrated in previous research. 2.3. Analyses For each of the 14 adverse life events, we report the mean impulsivity score of those who experienced the event and those who did not. We used t-tests to test for differences in mean impulsivity scores. We also report Cohen’s standardized effect coefficient (d ) as an indicator of the relative magnitude of association between impulsivity and each adverse life event. The adverse life events composite index was technically a count variable with possible scores ranging from 0 to 14. However, the observed distribution was unimodal and exhibited only moderate positive skewness. Exploratory analysis using the ladder and gladder procedures in Stata 8.2 (StatCorp, 2003) indicated that a square-root transformation generated an approximately normal response variable. Analyses using the transformed and untransformed response
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Table 2 Impulsivity and the experience of adverse life events Experienced life event
Too little money for needs Spouse/partner/lover break up Major physical fight Sexually assaulted Have children taken away Spent time in prison Time on street or in shelter Death of close friend/relative Fired or laid off job Major conflict friend/family Been arrested Contracted a STD Major accident Drug overdose
No
Yes
d
t (p)
10.11 (±4.78) 11.17 (±4.63) 11.12 (±4.50) 11.62 (±4.56) 11.46 (±4.58) 11.11 (±4.67) 10.89 (±4.61) 11.49 (±4.48) 11.31 (±4.59) 10.76 (±4.72) 11.16 (±4.67) 11.53 (±4.62) 11.42 (±4.64) 11.39 (±4.60)
12.13 (±4.42) 12.22 (±4.49) 12.57 (±4.67) 10.54 (±5.59) 14.00 (±4.44) 13.16 (±3.97) 12.32 (±4.48) 11.72 (±4.81) 12.54 (±4.52) 12.86 (±4.10) 12.76 (±4.22) 12.45 (±4.08) 13.17 (±3.87) 13.11 (±4.40)
.44 .23 .32 −.23 .55 .45 .31 .05 .27 .46 .34 .20 .38 .37
3.61 (<.001) 2.02 (.044) 2.68 (.008) −.83 (.408) 2.23 (.026) 3.45 (.001) 2.86 (.005) .44 (.664) 1.99 (.047) 4.13 (<.001) 2.77 (.006) .65 (.515) 1.97 (.050) 2.10 (.036)
variable yielded statistically consistent results. To simplify the presentation, we report results using the untransformed index of adverse life events as the response variable. OLS regression effects were estimated. Because analysis of residuals exhibited some heteroskedasticity, we used robust standard error estimates to calculate tests of statistical significance (StatCorp, 2003). The response variable and continuous predictor variables (age and impulsivity) were standardized to zero mean and unit variance prior to estimation. The effects for categorical predictor variables are y-standardized (Long, 1997), whereas the effects associated with continuous predictors are fully standardized. In bivariate analyses, we separately tested the effects of each of four current substance abuse/dependence diagnoses (alcohol, opioid, cocaine, and cannabis). Readers should note that in this cohort we are generally not comparing those with a specific diagnosis to those with no substance-related diagnosis. Indeed, only 28 (8.5%) participants did not meet diagnostic criteria for current abuse/dependence criteria for any of these four substances, and only 10.6% did not meet diagnostic criteria for current opioid or cocaine abuse/dependence. Just over 53.3% met criteria for current abuse/dependence on at least two different substances (30.0% for both opioid and cocaine). Therefore, we constructed a count variable indicating the number of current abuse/dependence diagnoses to determine if those with multiple diagnoses were more likely to experience adverse life events. Though not presented in tabular form, we also tested the first-order interaction for all pairs of substance-related diagnoses (e.g., opioid by alcohol, opioid by cocaine) to determine if specific combinations of substance-related disorders were especially likely to be associated with adverse life events.
3. Results A majority of the 330 participants were male (62.1%), just over half (54.6%) were Caucasian, and they aver-
aged 38.92 (±9.23) years of age. Participants reported using heroin and/or cocaine for an average of 18.19 (S.D. = 9.16) years. Among heroin users, the average age of initiating heroin use was 24.83 (S.D. = 8.35) years; among cocaine users, the average age of initiating cocaine use was 22.11 (S.D. = 8.02) years. The mean ASI drug composite score was 0.267 (S.D. = 0.132). With respect to SCID diagnoses, 96 participants (29.1%) met criteria for current alcohol abuse/dependence, 183 (55.5%) for current opioid abuse/dependence, 76 (23.0%) for current cannabis abuse/dependence, and 211 (63.9%) for current cocaine abuse/dependence. Over half the sample (176 individuals, or 53.3%) met criteria for more than one substance abuse/dependence diagnosis. Thirty-five individuals (10.6%) did not meet criteria for current cocaine or opioid abuse/dependence. Only five individuals (1.5%) did not meet criteria for lifetime cocaine or opioid abuse/dependence. Observed impulsivity scores ranged from 0 to 19 (the theoretical minimum and maximum scale scores) and averaged 11.56 (±4.60). These individuals experienced considerable exposure to adverse life events in the prior 6 months (Table 1). The observed range of scores on the adverse life events index was 0–13 (a score of 14 was the highest possible value). On average, participants reported 3.66 (±2.37) adverse life events. Only 6.1% of the sample reported experiencing none of the listed adverse life events during this assessment period. Impulsivity was associated significantly with 11 of the 14 adverse life events (Table 2). Higher mean impulsivity was significantly associated with having too little money to meet needs, breaking up with a spouse, partner, or lover, being in a major physical fight, having children taken away, spending time in prison, spending time on the street or in a shelter, being fired or laid off from a job, having a major conflict with friend or family member, being arrested, having a major accident, and having a drug overdose in the last 6 months. Impulsivity was not significantly associated with being sexually assaulted, experiencing the death of a close friend or
J. Hayaki et al. / Drug and Alcohol Dependence 78 (2005) 65–71
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Table 3 Unadjusted and adjusted effects of selected predictor variables on the expected number of adverse life events Unadjusted effects
Age Gender (male) Ethnicity (caucasian) Alcohol abuse/dependence Opioid abuse/dependence Cannabis abuse/dependence Cocaine abuse/dependence #Abuse/dependence diagnosis Impulsivity
Adjusted effects
ba
(p)b
t
−.123 −.000 .139 .237 .174 .249 .111 .160 .289
−2.28 (.023) −.00 (.998) 1.26 (.210) 1.88 (.062) 1.57 (.118) 1.85 (.065) .95 (.341) 2.64 (.009) 5.22 (.000)
ba
t (p)b
−.006 −.020 .106
−1.11(.267) .18(.853) .99(.324)
.094 .254
1.71(.088) 4.62(.000) R2 = .10
a b
Effects for continuous variables age and impulsivity are fully standardized. Effects for dichotomous predictors are y-standardized (see Long, 1997). Reported test statistics are based on robust standard errors. Model-based standard errors were of similar magnitude and gave consistent results.
relative, or contracting a sexually transmitted disease (STD) (Table 2). Table 3 presents the unadjusted and adjusted effects of selected predictors on the index of adverse life effects. Bivariate analysis indicated a significant inverse association between age and adverse life events; however, this association was sharply attenuated and not statistically significant when adjusted for other covariates included in the full model. The number of reported adverse life events was not significantly associated with other background characteristics such as gender or race. The gender by impulsivity interaction did not contribute significantly to the model and is therefore not presented here. None of the current substance (alcohol, opioid, cannabis, cocaine) abuse/dependence diagnoses were significantly associated with the index of adverse life events at the conventionally accepted p < .05 level (Table 3). The association between number of abuse/dependence diagnoses and adverse life events was substantively attenuated and became non-significant when adjusted for impulsivity. Finally, adverse life events were positively associated with impulsivity, both in bivariate analyses and in the final model. In addition, this model was repeated with the ASI drug composite index as the measure of substance use severity (rather than the individual SCID diagnoses and number of SCID diagnoses) and yielded virtually identical results. To determine whether specific combinations of substancerelated disorders were especially likely to be associated with higher rates of adverse life events, we tested the first-order interaction between the six possible pairs of specific disorders. Probability values for these tests ranged from .301 for the first-order cocaine abuse/dependence by cannabis abuse/dependence to .841 for the first-order cocaine by alcohol interaction effect. These data provided no evidence that specific combinations of drug disorders are more likely associated with especially high rates of adverse life events. Finally, we ran additional analyses specifically to explore the pattern of association among number of abuse/ dependence diagnoses, adverse life events, and impulsivity. Impulsivity and number of substance-related diagnoses were
significantly associated in the bivariate analysis (r = .237, p = .000). The association between the number of current substance-related disorders and adverse life events was statistically significant when adjusted for age, gender, and ethnicity (b = .150, t = 2.45, p = .015). However, when impulsivity was included in the model, the effect of number of substancerelated diagnoses weakened and was no longer statistically significant, as described above (Table 3).
4. Discussion The participants in this study reported a high frequency of adverse life events in the 6 months prior to the interview. This finding is consistent with previous reports that substance abusers experience heightened adversity (e.g., Kosten et al., 1986). What is especially remarkable is that only 6.1% of all participants reported no adverse life events in the past 6 months, suggesting that disturbingly event-filled lives were the norm in this sample of substance users. What cannot be addressed here is whether these experiences predispose substance users to use drugs more frequently, or whether they are actual consequences of the substance use itself. Results also indicate that impulsivity was able to distinguish between individuals who did or did not endorse all but three of the 14 adverse life events. Exceptions were sexual assault, death of a close friend or relative, and contracting a sexually transmitted disease. In the case of sexual assault and STDs, it is possible that the association with impulsivity was non-significant due to the low endorsement rate for these events. It is also possible that one’s trait impulsivity would not necessarily impact an outcome such as death of a close friend or relative that is beyond one’s behavioral control. For each of the 11 remaining items, those who endorsed the item scored significantly higher on the impulsivity measure. This finding supports the notion that impulsive individuals are more likely to behave in ways that put them at risk for negative life events. Of course, a causal relationship cannot be inferred from these cross-sectional findings. However, given that a trait measure
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of impulsivity was used, whereas adverse life events were assessed only in the previous 6 months, it is likely that impulsive tendencies predated the occurrence of the negative life events. Indeed, impulsivity was operationalized in terms of behaviors reflecting a general tendency to act quickly without plan or regard to consequence. As such, the assessment of impulsivity was not temporally bound, but rather reflected an overall, presumably somewhat stable, characteristic of the individual. In contrast, the assessment of adverse life events was temporally limited to the past 6 months, suggesting a more recent timeframe. In this sample, no single substance-related abuse/dependence diagnosis was significantly associated with adverse life events in bivariate analyses. However, as noted previously, this was a drug-using sample, almost all of who met criteria for at least one substance abuse/dependence diagnosis. Therefore, although these bivariate associations trended in the expected direction, for each individual substance, drug users meeting diagnostic criteria were essentially compared to other drug users meeting diagnostic criteria for at least one other substance, as opposed to a non-substance using control group. Given our sample selection, in order to examine whether specific combinations of diagnoses were associated with greater adversity, first-order interactions among the possible pairs of substance diagnoses were also tested. These subsequent analyses demonstrated that no specific combination of substance-related diagnoses was associated with greater adversity, suggesting that, among substance users, the likelihood of adverse life events is not linked to any specific pattern of substance abuse. That the number of substancerelated diagnoses was associated with adverse life events in bivariate analyses indicates that it is perhaps the severity of substance abuse, rather than the specific substance or substances used, that increases the likelihood of adverse life events. This study has the following limitations. First, substance use severity was primarily defined as the number of current DSM-IV (APA, 1994) alcohol/substance abuse or dependence diagnoses for four drug classes that are commonly used and/or abused in this population. This categorical approach does not capture non-diagnostic substance use that may otherwise have impacted results. (However, it should be noted that the statistical model was also tested using the drug composite index of the ASI, with virtually identical findings.) Of related concern, the study utilized exclusively self-report instruments. The use of self-report measures is common in previous research on impulsivity (e.g., Allen et al., 1998). Nonetheless, the frequencies of adverse life events were extremely high for many items considering the 6-month timeframe of the assessment. It is possible that participants either misremembered or misrepresented the adversity in their lives or responded to the probes with a different timeframe than that stated in the instructions. Another possibility is that the amount of adversity in this sample was higher than in other groups of substance users. For instance, the use of a monetary incentive for participation may have preferentially
drawn those substance users with worse life circumstances. A different sample of drug users may have provided different absolute values of adverse events, and the added presence of a non-substance using comparison group could have provided another context in which to interpret the reported frequencies. A final limitation of the present study was the use of a unidimensional definition of impulsivity. Although the impulsivity subscale of the Eysenck I7 Questionnaire is a widely used measure of trait impulsivity that has performed well in other samples of substance abusers (e.g., Alessi and Petry, 2003), it nonetheless represents only one aspect of impulsivity. The fact that this particular subtype of impulsivity uniquely predicted the experience of adverse life events suggests that it was an appropriate choice for the questions addressed here. However, it is also possible that alternative dimensions of impulsivity may also carry predictive power, especially if each dimension explains a different aspect of substance abuse, as has been suggested previously (Lane et al., 2003). Trait impulsivity may develop early in life, triggering the onset of substance use or the occurrence of adverse life events. For instance, the tendency to take risks and act without regard to consequence may manifest in poor behavioral choices and heighten the likelihood of using and abusing substances or experiencing adverse life events. However, recent evidence shows that the excessive use of certain substances causes neurological deficits associated with impulsivity (e.g., Morgan, 1998). Therefore, it is possible that problematic substance use elicits impulsive behavior, which then leads to adversity. It is also possible that experiencing adverse life events may exacerbate impulsive tendencies or serve as a precursor to substance use. To determine temporal sequence, these models require prospective measurement. This study has quantified recent adverse life events in a large sample of illicit drug users. In addition, results demonstrated a unique association between these adverse life events and a measure of trait impulsivity that is above and beyond the shared relation with demographic variables, substance abuse and dependence, and number of substance-related diagnoses. Of particular interest, the association between number of abuse/dependence diagnoses and adverse life events was attenuated and not statistically significant when adjusted for impulsivity. Although these data were not sufficient to determine temporal ordering, the pattern of results was consistent with an explanation in which impulsivity partially mediates the association between number of substance-related disorders and adverse life events. A second plausible explanation is that impulsivity is a relatively enduring trait that at least partially accounts for the association between number of substance-related disorders and number of adverse life events. Longitudinal data are needed to disentangle the temporal order. These findings therefore lend non-temporal support to the notion that impulsivity is a risk factor for the experience of adverse life events and has implications for targeting clinical intervention. Future studies should replicate these findings in other groups of illicit drug users using longitudinal study designs.
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Acknowledgments This study was funded by the National Institutes of Health Grants #MH62719 and DA13759. Dr. Stein is a recipient of a Mid-Career Investigator Award from the National Institute on Drug Abuse (K24 DA00512). We are grateful to two anonymous reviewers for their helpful comments and suggestions. Finally, we acknowledge Peter Friedmann and Susan Ramsey for comments on earlier drafts.
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