In our third and fourth sets of models, we adjusted for age and parenting variables and age and peer variables, respectively. In our fifth set of models, we adjusted for covariates that were significant in models 2-4. Third, we tested whether age modified the effect of our exposures by including a product term between exposure and each age spline. Significant effect measure modification was then probed to clarify how the association between psychiatric problems and substance use changed across the age splines. We conducted a sensitivity analysis to establish the directionality of the association between psychiatric problems and substance use. We thus estimated, with linear fixed effects models, the effect that changes in one-year-lagged substance use had on change in psychiatric problem domains in the following year. We followed the same modeling strategy for these models as we did with our primary models. We adjusted for groups of confounders as described above, first adjusting for SES, psychiatric problem domains that were not modeled as the outcome , and measures of substance use that were not the exposure of interest . Next we adjusted for parenting variables and peer variables, respectively. Finally, we adjusted for covariates that were significant in any of the previous groups of confounder models. Covariates were lagged one year prior to the exposure measure , to avoid blocking the causal pathway between substance use and psychiatric problems. Table 1 shows mean substance use and psychiatric problem counts over time, as well as demographic characteristics at baseline. The reports of particular informants in our psychiatric problem measures did not influence the associations between psychiatric problems and substance use . Table 2 displays the exponentiated coefficients and confidence intervals of quasiPoisson models,vertical greenhouse growing systems which can be interpreted as rate ratios. Table 2 shows the rate of substance use associated with a one-unit within-subject change in lagged psychiatric problems.

Changes in lagged conduct problems were positively associated with changes in marijuana frequency. During years in which adolescents experienced a one-unit increase in conduct problems, the rate at which they smoked marijuana the following year increased 1.03 times : 1.01, 1.05. For a standard deviation change in conduct problems, this is equivalent to a 1.15 times higher rate of marijuana use frequency . The magnitude of this association did not change appreciably after adjusting for potential confounders, including alcohol quantity and frequency, SES, affective and anxiety problems, parenting, and peer deviance. Changes in lagged conduct problems were also associated with changes in alcohol quantity, only after adjusting for peer deviance. During years in which adolescents experienced a one-unit increase in conduct problems, the rate of their average alcohol consumption per occasion the following year increased by 1.01 . For a standard deviation change in conduct problems, this is equivalent to a 1.05 times higher rate of alcohol use . Associations of all covariates with substance use are presented in Appendix C, Table C1. Table 3 presents results for tests of effect measure modification of the association between conduct problems and marijuana frequency and alcohol quantity by age. Because splines are polynomial functions, there is no simple quantitative interpretation of individual effect modification terms; however, the significance of the coefficients implies that the associations between lagged conduct problems and marijuana frequency, and lagged conduct problems and alcohol quantity, differed by age. For ease of interpretation we present these results in Figure 1, which shows the predicted values of substance use outcomes associated with minimum, mean, and third-quartile levels of lagged conduct disorder T-scores, over time. Compared to minimal changes in lagged conduct problems, adolescents with mean or third-quartile levels of change in lagged conduct problems show markedly different marijuana frequency trajectories, which become the most disparate at ages 17-19.

Compared to minimal changes in lagged conduct problems, adolescents with mean or third-quartile levels of change in lagged conduct problems show higher alcohol quantity in early adolescence but lower alcohol quantity in later adolescence. The results of our sensitivity analysis are presented in Table 4 and 5, and Figure 2. Table 4 displays the change in psychiatric problems associated with a one-unit change in lagged substance use in the prior year. There was one reverse association: while changes in lagged anxiety problems were not associated with changes in substance use, the opposite did occur: changes in lagged alcohol quantity in the past year were positively associated with changes in anxiety problems. During years in which adolescents experienced a one-unit increase in the average quantity of alcohol consumed when drinking, their anxiety problems T-score increased the following year by 0.12 . For a standard deviation change in average alcohol quantity, this is equivalent to an anxiety T-score increase of 0.3 . The magnitude of this association did not change appreciably after adjusting for potential confounders. Associations of all lagged covariates with psychiatric problems are presented in Appendix C, Table C2. Table 5 presents results for tests of effect measure modification of the association between lagged alcohol quantity and anxiety problems by age, and Figure 2 shows the predicted values of anxiety problem T-scores associated with minimum, mean, and third-quartile levels of lagged alcohol quantity, over time. Adolescents show a decline in anxiety problems throughout adolescence, and little difference by the magnitude of fluctuations in lagged alcohol quantity. However, deviations arose at ages 13-14 and 17-19, where those who exhibited a mean or third-quartile level of increase in lagged alcohol quantity showed slower declines in anxiety problems compared to those who did not increase alcohol intake over time. This study focused on the longitudinal relationship between changes in psychiatric problems and changes in substance use one year later. However, the temporal resolution of this relationship may occur on a much shorter time frame – that is, changes in psychiatric problems may have immediate effects on substance use . To approximate effects on such a short time frame, we also examined the association between change in psychiatric problems and contemporaneous change in substance use. We followed the same modeling strategy as in our primary models, but adjusted for one-year-lagged versions of all covariates . Table 6 presents the rate of contemporaneous changes in substance use frequency associated with changes in psychiatric problem T-score.

In fully adjusted models, within person changes in the conduct problems T-score were associated with contemporaneous changes in marijuana frequency, alcohol frequency, and alcohol quantity. Within-person changes in the affective problems T-score were associated with contemporaneous changes in alcohol quantity. Associations of all covariates with substance use in the contemporaneous models are presented in Appendix C, Table C3. This study examined whether adolescent males tend to escalate their substance use following an increase in their psychiatric problems, and identified periods during adolescence when such associations may be particularly strong. We found that when youth experienced an increase in conduct problems, they showed an increase in the frequency of marijuana use and quantity of alcohol use in the following year. Fluctuations in conduct problems and affective problems may have an influence on alcohol use on a shorter time scale: changes in conduct problems and affective problems were concurrently associated with changes in alcohol frequency and quantity, respectively, in the same year, but not in the subsequent year. The specific effect of conduct problems on substance use is consistent with the notion that conduct disorder problems and substance use constitute elements within a broader externalizing spectrum.Although numerous longitudinal studies have demonstrated that youth with psychiatric problems are at increased risk for using and abusing substances , few have examined whether adolescents tend to increase their substance use following periods when they experience an increase in their psychiatric problems .By focusing on within-individual change, we were able to rule out the possibility that selection effects and stable individual differences between youth with differing levels of psychiatric problems and substance use accounted for the observed association between psychiatric problems and substance use. Further,vertical grow kit the use of an extensive set of measures of potential time-varying covariates , allayed concerns that the associations were confounded by time-varying factors. The strength of the associations between conduct disorder problems and marijuana and alcohol use were relatively modest, suggesting that a substantial change in conduct problems would have to occur to produce a substantial within-individual change in substance use. This is consistent with prior studies that have tried to predict change over time in substance use 10. Substance use is shaped by multiple risk factors working together – hence, any one risk factor is likely to make a modest contribution to within individual fluctuations in substance use. This study examined the bidirectional nature of the association between psychiatric problems and substance use, and found evidence of a reverse effect of substance use on psychiatric problems. While increases in anxiety and depression did not result in increases in substance use, increases in the quantity of alcohol use did result in increases in anxiety problems. The effect of alcohol use on anxiety problems is consistent with prior studies that have found that substance use increases the risk for anxiety disorders.There are at least two possible explanations for this observed pattern. First, substance use can increase exposure to economic and social problems that increase the risk for anxiety, including crime, unemployment, loss of income, and relationship problems.Second, substance use can cause neurochemical changes which increase vulnerability to an anxiety disorder.

The effect of conduct disorder problem fluctuations on quantity of alcohol use was strongest in early adolescence, while the effect of conduct disorder changes on marijuana use was strongest in late adolescence . At the same time, the effect of quantity of alcohol use on anxiety was strongest in early and late adolescence . Two points are worth noting about this pattern. First, life transitions such as the shift from middle school to high school in early adolescence and the shift from high school to college in late adolescence may escalate existing challenges produced by fluctuations in psychiatric problems or substance use.For example, Jackson et al. found that the prevalence of heavy drinkers more than doubled in the transition to high school and that this change was especially pronounced for youth with more problem behaviors. Studies of the transition from adolescence to young adulthood have also found that post-secondary school attendance predicted higher rates of substance use, and that the relationship between conduct problems and substance use was stronger in late adolescence than in middle adolescence.Pronounced effects of psychiatric problem and substance use fluctuations at times of transition would be consistent with an accentuation model , whereby the stress of the transition and the demands of the new context reduce contextual limitations on individual proclivities, potentially allowing for fluctuations in psychiatric problems to have a stronger effect on substance use, and vice versa. Second, the larger effect of conduct disorder on alcohol use at earlier ages and on marijuana use at later ages may reflect the developmental timing of these two substances. Drinking starts in early to mid-adolescence; hence, fluctuations in conduct problems in early adolescence may lead to involvement with alcohol use, as the drug that is most easily available in families and peer groups. In contrast, marijuana use typically starts in mid- to late adolescence, so the influence of conduct problems on marijuana use may increase as access to marijuana becomes easier in later ages.The study findings should be taken in light of the following limitations. First, all participants in the Pittsburgh Youth Study are male; hence, we could not examine the relationship between psychopathology and substance use quantity and frequency among girls. Second, all participants were selected from Pittsburgh public schools, which potentially limits the generalizability of the findings beyond this area. Third, half of the sample was composed of high-risk boys: this limited our ability to infer to the general population, but also provided us with greater power to detect an association between fluctuations in psychiatric problems and substance use. Fourth, while we examined measures of psychiatric problems that are consistent with DSM diagnoses, these measures did not explicitly measure diagnostic criteria for DSM disorders. Grouping symptoms into “affective”, “anxiety” and “conduct” problem categories might merge stronger individual disorders with non-predictors of substance use, leading to an underestimate of the association between psychiatric problems and substance use. However, it is increasingly recognized that psychiatric problems are best conceptualized as falling on a continuum of severity rather than representing a discrete taxon. Fifth, a low base rate prevented us from examining the predictors of fluctuation in the level of use of other illicit drugs. Sixth, the prevalence of marijuana use has increased since the completion of this study.