Abstract
Externalizing symptoms robustly predict adolescent substance use (SU); however, findings regarding internalizing symptoms have been mixed, suggesting that there may be important moderators of the relationship between internalizing problems and SU. The present study used a longitudinal community sample (N = 387, 55% female, 83% White) to test whether externalizing symptoms moderated the relationship between internalizing symptoms and trajectories of alcohol and marijuana use from early (age 11-12 years old) to late (age 18-19 years old) adolescence. Two-part latent growth models were used to distinguish trajectories of probability of use from trajectories of amount of use among users. Results suggested that externalizing symptoms moderated the association between internalizing symptoms and probability of alcohol, but not marijuana use. The highest probability of alcohol use was observed at high levels of externalizing symptoms and low levels of internalizing symptoms. A negative protective effect of internalizing symptoms on probability of alcohol use was strongest in early adolescence for youth high on externalizing symptoms. Although moderation was not supported for amount of use among users, both domains of symptomology were associated with amount of alcohol and marijuana use as first-order effects. High levels of externalizing symptoms and low levels of internalizing symptoms were associated with high levels of amount of use among users. These findings suggest that developmental models of substance use that incorporate internalizing symptomology should consider the context of externalizing problems and distinguish probability and amount of use.