Prediction of intravenous drug use

Prediction

of Intravenous

Drug Use

Stephen H. Dinwiddie, Theodore Reich, and C. Robert Cloninger Information about lifetime intravenous drug use (IVDU) was obtained from 1,062 relatives of hospitalized alcoholics, felons, and control subjects, of whom 92 had a history of IVDU and an additional 230 had a history of substantial, but non-IV drug use. The IVDlJs were significantly more likely than all other subjects to have reported experiencing numerous behavioral and social difficulties relating to conduct difficulties, early initiation of substance use, and disrupted living situation before the age of 15. They were also more likely to

N

UMEROUS STUDIES have indicated that behavioral problems in childhood and early adolescence are predictive of later substance use and abuse.’ Adolescent drug users have been shown to exhibit a number of behavioral difficulties, including disciplinary problems at school, poor academic performance, and early onset of sexual behavior2-4; and, while such behaviors might be a consequence of substance abuse, there is evidence to indicate that conduct difficulties often occur before the onset of substance use.z,5-7 Familial factors, both prenatal and postnatal, also appear to have an influence on vulnerability to substance use. Alcohol abuse, for example, appears to be influenced by both constitutional and environmental factors, although specific factors remain to be elucidated.8-r0 Other studies have attempted to demonstrate familial inheritance of other substance abuse as well,rl-I6 although this has proven to be a difficult task owing to the multiplicity of drugs available and the changing nature of their abuse over time. The high prevalence of comorbid psychiatric illness, especially alcoholism, antisocial personality disorder (ASP), and affective disorder17-X6 among substance abusers further complicates the interpretation of such studies. Factors in the family environment have also been correlated with later alcohol abuse, including inconsistent and harsh disciplinary practices” and disruption of “family rituals” surrounding alcohol use.28-30Less is known about home environmental factors that might predispose toward other substance use, although evidence suggests that it may be promoted by the child having a poor relationship with parents or by modeling on parental drug or alcohol abuse.4.31 Other factors shown to be associated

have exhibited conduct problems than other drug users. In multivariate analyses, four symptoms (fighting in school, juvenile arrest, initiation of cannabis use before 15, or initiation of sexual activity before 15) differentiated IVDUs. A history of greater numbers of these problems was associated with increasing risk for IVDU, both when compared with the total sample and when compared with other drug users. Copyright 0 7992 by W.B. Saunders Company

with initiation of drug use in adolescence, such as poor academic motivation and involvement in antisocial activity,4 might also in part be related to inadequate parental supervision. Given that substance abuse is associated with a variety of family and behavioral characteristics that precede its onset, it should, in principle, be possible to construct a profile of those at high risk. Such a profile would be especially useful if risk of severe drug abuse could be evaluated substantially before onset of drug use, so that prevention efforts among high-risk individuals could be made either before drug use was initiated or before it progressed in severity. Along these lines, in an effort to identify early predictors of intravenous drug use (IVDU), Tomas et a1.32compared 222 self-referred, primarily minority, IVDUs with 588 subjects from the Baltimore site of the Epidemiologic Catchment Area (ECA) study who were matched on gender and area of residence. Data were available from both IVDUs and controls on nine behavioral problems occurring before the age of 16: running away from home, fighting, vandalism, disciplinary problems at school, truancy, suspension or expulsion, theft, arrests as a juvenile, and frequent lying. While the degree to which each behavior was associated with later

From the Deparrments of Psychiatry and Gerretrcs, Washington Universiry School of Medicine and Jewish Hospital, St Louis, MO. Supported by Grants No. MH-46276, A&0840/, and AA08403 (S.H.D.); MH-46280, MH-45522. and MH-31302 (TR.), and MN-AA0828 (C.R.C.). Address reprint requests to Stephen H. Dinwiddie, M.D.. Department of Psychiatry, Jewish Hospital of St Louis, 216 S Kingshighway, St Louis, MO 631 IO. Copyright 0 I992 by W.B. Saunders Company OOlO-440X/9213303-0013$03.00l0

Comprehensive Psychiatry, Vol.33, No. 3 (May/June),1992:pp 173-179

173

DINWIDDIE, REICH, AND CLONINGER

174

IVDU was not reported, the investigators found that having had more of these problems correlated with increased risk for IVDU: those with moderate scores (three to six of the nine behavioral problems evaluated) were over seven times as likely to become IVDUs, while those with seven or more problems were nearly 25 times as likely to be IVDUs. We previously reported that a history of solvent use was modestly predictive of IVDU.33 The present study is an attempt to extend that work in the same sample, and in this population, to replicate the findings of Tomas et a1.32 In particular, we wished to learn whether the behaviors studied by Tomas et a1.32were characteristic of IVDUs in general and whether IVDUs could be differentiated on the basis of early behavior both from the general population and from subjects who later used illicit drugs heavily, but who had never injected. METHOD

Assessment Subjects were drawn from a family interview and follow-up study of alcoholism conducted by T. Reich and CR. Cloninger at Washington University.33 Probands in the initial study consisted of alcoholics admitted for inpatient treatment, felons ascertained through the office of probation and parole, or control subjects admitted to the university hospital’s medical and surgical services. Data from the probands were not analyzed due to the likelihood of biasing the sample toward more severe behavioral disturbance. Data from 1,062 interviewed relatives age 42 or younger (the age at interview of the oldest IVDU) were included. Information on early home environment, behavior before the age of 15, and lifetime drug use was obtained by use of the Home Environment and Lifetime Psychiatric Evaluation Record (HELPER).34 Subjects were divided into four mutually exclusive categories based on lifetime drug use: those who reported no illicit drug use; those who reported use of cannabis but no other illicit drugs more than five times (“cannabis users”); subjects who used stimulants, sedative-hypnotics, opiates, hallucinogens, or solvents more than five times, but who denied ever injecting drugs (“other drug users”); and those who reported any lifetime history of IVDU.

Statistical Analysis Statistical analysis was performed using SAS version 5.35 Data were analyzed using chi-square tests, with continuity correction where appropriate. Two-tailed probabilities are reported for all tests. Because some of the comparison group members would not have passed through the period of risk for IVDU, data were anaIyzed using the technique of surviva1 anaIysis36.-” Survival analysis is used in cases where the variable of

interest “T” is time to an event, for example time to onset of IVDU. The probability of being unaffected at time “t” may be written as a survival function S(t), where S(t) = 1 Pr(T 5 t). This may be estimated by a Kaplan-Meier “step function” where, at the outset, all subjects are unaffected, i.e., S(t) = 1.0. Over time, as subjects change status from unaffected to affected, the curve drops, with the magnitude of the drop dependent on the number at risk, which in turn will decrease as the number of unaffected subjects decreases. If an individual is unaffected at time t (that is, the hypothesized value of T is greater than his current age), the observation is censored, that is, data from that individual can be used in calculating S(t) only up to that point. A second function. the hazard function, A(t), is defined as the risk of becoming affected at time t conditioned on having remained unaffected up to that point. In the Cox proportional hazards mode1,s6 no assumptions are made regarding the shape of the survival curve, but the assumption is made that the curves for different individuals are parallel, that is, that any covariates are assumed to act multiplicatively on the hazard function. For this analysis, the PHGLM procedure of SAS3” was employed. For all models, socioeconomic status, marital status, and group of ascertainment were included as covariates. Since preliminary analyses showed that the assumption of proportionality by gender was violated, final models were stratified by gender. The data set was examined for symptoms that were considered a priori to be likely to be related to later IVDU, including the nine symptoms evaluated by Tomas et aL3? (One of the symptoms used by Tomas et al., fighting as a juvenile, was collected in our data set as fighting in school only and therefore may be more restrictive.) To minimize the overlap with sequelae of sustained drug use, only symptoms with onset before 15 years of age were counted. Those symptoms that individually were significantly related to later IVDU both when compared with all relatives and when compared with other drug users were then evaluated in stepwise multivariate functions; those that remained significant were then used to devise a scale to predict risk of IVDU, where presence of each symptom added 1 point to the total. Sensitivity, specificity, and positive predictive values for IVDU were then calculated for each score on this scale.

RESULTS

Table 1 shows the demographic differences between groups. Of the 1,062 subjects, 411 reported no illicit drug use, 329 cannabis use but no other significant drug use, 230 other drug use, and 92 reported injecting drugs. JVDUs were more likely to be men and tended to report lower socioeconomic status. All drug users were significantly younger than non-drug users. Mean age of onset of IVDU was 18.5 -t 3.4 years, and ranged from 13 to 30 years. To avoid confounding behveen IVDU and its putative predictors, the seven subjects with onset of

PREDICTION OF INTRAVENOUS

DRUG USE

175

Table 1. Demographic Comparisons No

Drug Use

Cannabis Only

Other Drug Use

IVDU

(N = 411)

(N = 329)

(N = 230)

(N = 92)

N i%)

N 1%)

N (%I

N (%)

Male

139 (33.8)

154 (46.2)

124 (53.9)

61 (66.3)

Female

272 (66.2)

175 (53.2)

106 (46.1)

31 (33.7)

Variable

Y2

P

Gender

45.443

< .OOl

143.862

< ,001

25.494

< ,001

Marital status Single

44 (10.7)

123 (37.4)

106 (46.1)

38 (41.3)

Married

326 (79.3)

170 (51.7)

84 (36.5)

43 (46.7)

Sepldiv

41 (10.0)

36 (10.9)

40 (17.4)

11 (12.0)

Alcohol

182 (44.3)

151 (45.9)

96 (41.7)

43 (46.7)

Control

84 (20.4)

39 (11.9)

20 (8.7)

77 (12.0)

145 (35.3)

139 (42.3)

114 (49.6)

38 (41.3)

31.5 * 7.0

25.1 t 6.5

24.3 -’ 5.6

24.1 + 5.2

Group

Felon Age at interview

t = 738.O.P Socioeconomic status (median rank)

2

< .OOl*

3 2=3.11o,P=.oo22*

t = 563.9, P < .OOl* 3 z = 2.980, P = .0029*

t = 175.6,P

< .OOOl*

4 z = 3.096, P = .0020*

*Two-way comparisons to “no drugs” group.

IVDU before age 15 were excluded from further analysis. Age-of-onset data were not available for another 11, leaving 74 subjects for whom age-of-onset data were available. For those subjects, mean age of onset of IVDU was 18.9 + 3.2 years, ranging from 15 to 30 years; only 13 subjects began IVDU after the age of 21. Problem behaviors occurring before age 15 that were evaluated for relationship with IVDU were selected from three classes of items: conduct problems (juvenile arrest, truancy, suspension or expulsion from school, running away from home, vandalism, fighting, seeing the principal, hyperactive behavior or being told that one is hyperactive, lying, theft or onset of sexual activity before the age of 15); early exposure to psychoactive substances (use of alcohol, cannabis, or solvents before the age of 15); and home environment factors (poor supervision or neglect, living apart from parents, parents heavy drinkers or drug users, parental divorce, or marked conflict with parents up to age 15). Table 2 shows the population rates for these 20 behaviors. It should be noted that these comparisons did not take into account differences in age structure, proportion of men and women, or other demographic differences between the three groups, and no corrections for multiple comparisons are made here. Rates tended to be lowest among those with no history of illicit drug use, rising steadily among canna-

bis users and other drug users, and were highest among IVDUs. Next, risk ratios for behaviors found to be significantly associated with IVDU were evaluated for relationship with IVDU using survival analysis. Individually, presence of each of these items was associated with an increased risk for later IVDU as compared with the entire sample, with risk ratios ranging from 1.69 to 6.78. When compared only to other drug users, risk ratios decreased and some items appeared to convey no added risk for IVDU (Table 3). The behaviors evaluated by Tomas et al.“’ were found in our sample as well to be significantly related to IVDU. These items were therefore given a score of 1 if present and 0 if absent and total scores used to predict IVDU, as previously done by Tomas et al. Using the same division points as Tomas et al.,” the population was split into low- (zero to two problems), moderate- (three to six problems), or high- (seven or more problems) risk groups. Using survival analysis, in our sample, risk of IVDU in the moderate-risk group was 4.67 times that of the low-risk group (95% confidence interval, 2.83 to 7.70; P < .OOOl), while for the high-risk group, the risk was increased by a factor of 15.23 (95% confidence interval, 5.89 to 40.17; P < .OOOl). Examination of age-on-onset data showed that the majority (68 or 84%) of the 81 IVDUs for whom data were available began injecting

176

DINWIDDIE, REICH, AND

CLONINGER

Table 2. Behavioral and Environmental Characteristics Before Age 15 No Drug Use Problem

N=411

Cannabis Users

Other Drug Users

IVDUS

N = 239

N = 230

N = 74

Before

ODU ” IVDU only

X2

N i%)

Age 15

N (%)

N (O/o)

N (O/o)

P

(3 df 1

X2

P

(1 df)

Runaway

16 (3.9)

27 (8.2)

39 (17.0)

21 (28.4)

59.030

< ,001

3.918

Juvenilearrest

12 (2.9)

28 (8.5)

33(14.4)

22 (29.7)

64.849

<.OOl

7.931

,005

9 (2.2)

31 (9.4)

34 (14.8)

19 (25.7)

58.390

< ,001

3.889

,049 ,004

Vandalism Truancy

47 (11.4)

77 (23.4)

85 (37.0)

42 (56.8)

100.214

<.OOl

8.228

Suspension

15 (3.7)

38 (11.6)

43 (18.7)

25 (33.8)

72.195

<.OOl

6.497

,011

Fighting

29 (7.1)

41 (12.5)

37 (16.1)

27 (36.5)

51.484

<.OOl

12.817

<.OOl

Sex before 15

55 (13.4)

70 (21.3)

58 (25.2)

31 (41.9)

36.820

<.OOl

6.734

,009

l(O.2)

4 (1.2)

11 (4.8)

6 (8.11)

29.067

<.OOl

0.614

NS NS

Hyperactivity Alcohol use

69 (16.8)

99 (30.1)

120 (52.2)

42 (56.8)

108.755

<.OOl

0.306

Cannabisuse

0 (0.0)

36 (10.9)

43 (18.7)

20 (27.0)

93.153

<.OOl

1.885

NS

Solvent use

0 (0.0)

1 (0.3)

6 (2.6)

4 (5.4)

24.927

1.001

0.638

NS

68 (16.6)

98 (29.8)

90 (39.1)

39 (52.7)

63.418

<.OOl

3.685

NS

3 (0.7)

24 (7.3)

22 (9.6)

13 (17.6)

44.375

<.OOl

2.778

NS

Theft

48 (11.7)

116 (35.3)

107 (46.5)

47 (63.5)

138.199

<.OOl

5.805

,016

Parental divorce

67 (16.3)

73 (22.2)

45 (19.6)

19 (25.7)

5.981

NS

from parents

41 (10.0)

36 (10.9)

28 (12.2)

14 (18.9)

5.173

NS

Fosterplacement

13 (3.2)

10 (3.0)

10 (4.4)

7 (9.5)

7.586

NS

54 (13.1)

44(13.4)

38 (16.5)

17 (23.0)

5.922

NS

132 (32.1)

128 (38.9)

103 (44.8)

37 (50.0)

15.075

62 (15.1)

64 (19.5)

62 (27.0)

31 (41.9)

33.556

29 (7.1)

41 (12.5)

31 (13.5)

16 (21.6)

16.896

17 (4.1)

31 (9.4)

41 (17.8)

22 (29.7)

59.691

Saw principal Frequent lying

Livedapart

Any separation from family Parent heavy drinker

.002

0.421

NS

Discord with parents Parental

neglect

<.OOl .OOl

5.199

,023

2.252

NS

4.131

,042

Poor parental supervision

before age 22. Therefore, non-IVDUs over age 21 were considered essentially through the period of risk. Using stepwise logistic regression, seven variables occurring before age 15 maxi-

mally differentiated fighting, arrest, school tal supervision, and before age 15 (Table

Table 3. Behavioral and Environmental Characteristics: ProblemsBefore Age 15

<.OOl

IVDUs: cannabis use. truancy, theft, poor paren: onset of sexual activity 4). In this model, age but

Survival Analysis

Risk Ratio

Risk Ratio

ofIVDU (95% Cl)

of IVDU (95% Cl)

(All Subjects)

P

(v ODUs Only)

P

Runaway

3.68 (2.20-6.15)

< .OOOl

1.82(1.09-3.06)

.0226

Juvenilearrests

4.21 (2.52-7.05)

< .OOOl

2.64 (1.58-4.39)

.0002

Vandalism

2.83 (1.63-4.90)

Truancy

3.98 (2.49-6.36)

1.001

2.04(1.27-3.28)

Suspension

4.19 (2.52-6.94)

1.0001

2.54(1.54-4.21)

.0003

School fighting

3.45 (2.10-5.65)

<.OOOl

2.35(1.43-3.87)

.OOOB

Sexbefore

2.84 (1.75-4.62)

<.OOOl

2.18(1.36-3.49)

.OOll

Hyperactivity

3.42 (1.45-8.04)

.0048

1.69(0.72-3.95)

NS

Alcohol use

2.59 (1.60-4.18)

.OOOl

1.33(0.83213)

NS

Cannabisuse

4.74 (2.66-8.46)

Solvent use

6.78 (2.44-18.82)

.0002

2.09 (0.75-5.81)

Saw principal

2.28(1.42-3.68)

.0007

1.54(0.96-2.48)

Frequentlying

3.46 (1.88-6.36)

.OOOl

1.87(1.02-3.41)

.0431

Theft

3.65 (2.22-6.00)

1.86(1.15-3.01)

.0115

Parent heavy drinker

1.69(1.06-2.69)

Discordwith parents

3.00(1.88-4.78)

Parental neglect

2.35(1.35-4.10)

Poorparentalsupervision

3.26 (1.95-5.46)

.0002

<.OOOl

<.OOOl .0276

1.66(0.97-2.84)

2.31 (1.31-4.08)

NS .0032

.0040 NS NS

1.29(0.80-2.06)

NS

<.OOOl

1.95(1.22-3.11)

.0055

.0025

1.69(0.96-2.97)

<.OOOl

1.81(1.08-3.03)

NS .0230

PREDICTION

OF INTRAVENOUS

Table

4. Prediction

Fighting

before arrests

before

15

15

Cannabis

use before

USE

177

of IVDU: Multivariate

Predictor

Juvenile

DRUG

15

Model

Odds

95% Confidence

Ratio

Interval

P

4.03

(2.00-8.11)

2.72

(1.22-6.04)

,014

2.70

(1.08-6.72)

.0333

2.23

(1.07-4.65)

.0328

1.92

(0.99-3.74)

.0546

1.91

(1.01-3.58)

.0448

1.71

(0.97-3.38)

.0618

,001

at a cutoff of 4. Using the same scale, specificity and positive predictive values for different cutoff scores were then recalculated using only IVDUs and other drug users (sensitivity obviously was unchanged), again showing that the populations could be adequately differentiated.

Poor supervision before

15

Sex before Truancy

15

before

Theft before NOTE. nomic

Odds

15

15 ratios

adjusted

for gender,

age, and socioeco-

status.

no other demographic variables were significant and were therefore dropped from the final model. Although two of these factors were no longer statistically significant after age was added to the model, they were retained since the overall fit of the model dropped significantly if either were removed. Since the magnitude of risk for these seven variables was similar (the p-coefficient of only one item was outside the range of the coefficient & its SE of the median item), a seven-item scale was constructed in the same manner as previously described. Use of this scale in place of the individual items resulted in a slight but significant decrease in explanatory power (decrease in model ~2 from 208.696 to 191.593, P < .OOl), but area under the curve (AUC) decreased very little, from 0.872 to 0.867, indicating little difference in specificity and sensitivity between the models. Sensitivity, specificity, and positive predictive values for IVDU were then calculated at each score level (Table 5). As cutoff scores increased, other drug users made up increasing proportions of those falsely classified as IVDUs (falsepositives), e.g., 102 of 335 (30.4%) at a cutoff of 1, 61 of 153 (39.9%) at a cutoff of 2, 27 of 54 (50.0%) at a cutoff of 3, and nine of 17 (52.9%) Table 5. Sensitivity, Specificity, and Positive Predictive Value of IVDU Risk Scale Total Sample SCCW+

Other Drug Use Only Positive

Positive

Ino. of

SellsI-

Speci-

Predictive

Speci-

Predictive

DrObk?“Wl

tivitv

ficity

Value

ficity

Value

39.3%

1

89.2%

53.9%

16.5%

31.1%

2

68.9%

79.0%

25.0%

58.8%

45.5%

3

56.8%

92.6%

43.8%

81.8%

60.9%

4

35.1%

97.7%

60.5%

93.9%

72.2%

r5

23.0%

99.4%

81 .O%

98.6%

89.5%

DISCUSSION

In a Caucasian sample not ascertained through manifestations of drug use, who were interviewed before or during the early years of the acquired immunodeficiency syndrome (AIDS) epidemic, we found that IVDU was associated with the same symptoms as those reported by Tomas et a1.32in a study of self-referred, primarily minority IVDUs recruited after the AIDS epidemic was well underway. In both studies, early conduct problems including fighting, lying, theft, vandalism, truancy, suspension or expulsion from school, other school disciplinary problems, juvenile arrests, and running away from home were all differentially associated with IVDU; in both studies, a greater number of these behaviors was associated with higher risk for IVDU. This relationship held despite use of different statistical techniques and use of a different structured interview than those used by Tomas et al.‘? Given that in our sample IVDU was found to be very strongly associated with ASP,” it is not surprising that symptoms of conduct disorder would be predictive of IVDU, since ASP and drug use so frequently coexist. However, we found other symptoms, less directly associated with ASP, which also increased the risk of IVDU over that of the general population. While three of these symptoms (use of alcohol, cannabis, and solvents before the age of 15) might reflect a heightened liability for substance abuse, it may also be that this finding is simply a less direct link to ASP. It is well known, for example, that those with early onset of antisocial behavior appear to be at elevated risk for substance abuse3y.40;solvent use, in particular, has been associated with high rates of ASP,‘4.“1 and a history of solvent use by itself has been shown in this population to be a modest predictor of IVDU.33 Similarly, some of the other factors identified as predictors of IVDU, such as pronounced discord with parents or poor supervision by parents before age 15, may be directly related to

178

DINWIDDIE,

increased liability for drug abuse, or may be nonspecific factors which increase the likelihood of developing ASP, which in turn might influence the risk for IVDU. Using a stepwise regression procedure, as we did, is likely to capitalize on chance; the specific relationship of fighting, precocious sexual activity, use of cannabis, theft, truancy from school, poor parental supervision, and having been arrested before 15 to later IVDU is likely to be unique to our particular sample, and is of less importance than the observations that many problem behaviors occurring before 15 are associated with later IVDU, and that increasing number of these behaviors is consistently associated with higher risk for IVDU. While in our sampIe chance may to some extent have determined which of the factors evaluated were most predictive, it is striking that these factors group into three areas: conduct problems, early drug use, and disrupted home environment. Furthermore, whether the conduct disorder symptoms identified by Tomas et a1.32or the broader range of symptoms assessed in our sample are used to predict later IVDU, increasing numbers of these behaviors are associated with increasing risk of IVDU. These factors differentiated IVDUs from other drug users as well. Our evidence suggests that there are identifiable differences between those who go on to use drugs to a significant degree without injecting (the other drug users) and those who progress to IVDU. While a number of environmental factors (discord with parents, parental neglect, poor parental supervision, or heavy drinking by parents) were re-

REICH, AND CLONINGER

ported more frequently by IVDUs than by the general population, they generally did not differentiate between the two drug-using populations. Conduct problems, on the other hand, often did. This suggests that among those who have exceeded the threshold of liability for substance abuse, the decision to inject is differentially made by a subgroup which manifests behavioral difficulties in many spheres of activity. Both our study and that of Tomas et a1.32were retrospective in design. While the relationship of certain conduct problems to IVDU has been replicated in two markedly different populations, other findings, such as early onset of substance use and the effects of a disrupted home environment, still need to be confirmed. Further work also should be performed to better differentiate IVDUs not only from the general population, but also from the larger pool of drug users. This may ultimately lead to a more efficient, two-stage screening process, which first identifies those at risk for any form of drug abuse and then from that group distinguishes those at risk for IVDU or other forms of highly risky drug use. Such a process, if coupled with effective interventions, could eventually be of significant public health benefit. Prospective studies of high-risk populations are needed not only to improve our ability to identify and treat at-risk individuals, but also to evaluate the relationship of specific constitutional and environmental factors in the later development of severe drug abuse, and to further elucidate the role played by conduct problems in its genesis.

REFERENCES 1. Robins LN. Conduct problems as predictors of substance abuse. In: Schmidt MH, Remschmidt H (eds): Needs and Prospects of Child and Adolescent Psychiatry. Berne, Switzerland: Hans Huber, 1989:187-211. 2. Kandel DB. Epidemiological and psychosocial perspectives on adolescent drug use. J Am Acad Child Psychiatry 1982;21:328-347. 3. Windle M. A longitudinal study of antisocial behaviors in early adolescence as predictors of later adolescent substance use: gender and ethnic group differences. J Abnorm Psycho1 1990;99:86-91. 4. Kandel DB, Raveis VH. Cessation of illicit drug use in young adulthood. Arch Gen Psychiatry 1989;46:109-116. 5. Robins LN, Price RK. Adult disorders predicted by childhood conduct problems: results from the NIMH Epide-

mioIogic Catchment Area project. Psychiatry. 1991;54:116132. 6. Hammersley R, Morrison V. Effects of polydrug use on the criminal activities of heroin-users. Br J Addict 1987;82:899-906. 7. Rounsaville BJ, Anton SF, Carroll K, Budde D, Prusoff BA, Gawin F. Psychiatric diagnoses of treatmentseeking cocaine abusers. Arch Gen Psychiatry 1991;48:4351. 8. Cloninger CR, Bohman M, Sigvardsson S. Inheritance of alcohol abuse: cross-fostering analysis of adopted men. Arch Gen Psychiatry 1981;38:861-868. 9. Bohman M, Sigvardsson S, Cloninger CR. Maternal inheritance of alcohol abuse: cross-fostering analysis of adopted women. Arch Gen Psychiatry 1981;38:965-969.

PREDICTION OF INTRAVENOUS

DRUG USE

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