Disentangling developmental trajectories of childhood anxiety and depression symptoms in the prediction of adolescent substance use.

Adolescent substance use is comorbid with internalizing problems (e.g., anxious and depressive symptoms) and externalizing problems (EPs). Developmental researchers have linked early anxious and depressive symptoms to later substance use behaviours via an "internalizing pathway". Support for this pathway exists among young adults; however, evidence from prospective studies of adolescents has been inconsistent. Given the paucity of prospective studies in this area, the current study used a developmental framework to examine childhood anxiety and depression symptom trajectories as predictors of adolescent substance use and whether these relationships depend on sex and EPs. Children with and without EPs participated annually in an ongoing longitudinal study (N = 744; Time 1 age = 6.3-10.6). Youth completed self-report measures of anxiety and depression symptoms (Times 3-6) and substance use (Times 7-8). Parents and teachers completed measures of children's EPs (Time 0). Parallel process growth models showed that changes over time in childhood depression symptoms were significantly positively associated with adolescent alcohol/cannabis use, substance-related consequences, and total score of problematic substance use. Changes over time in childhood anxiety symptoms were significantly negatively associated with adolescent alcohol/cannabis use. These results were invariant by EPs and sex. Research implications of this study emphasize the importance of isolating the respective pathways of anxious and depressive symptoms to later substance use outcomes, while clinical implications focus on targets for early identification and prevention of problematic substance use in adolescence.