Methods: This study uses data from a cohort study of Baltimore youth (89% Black, 70% low SES) who were part of a preventive intervention in first grade and followed annually through age 26. Adjusted logistic regression analyses examine the potential impact of early onset marijuana use (before age 15) compared to later onset and to non-users on the development of major depression and generalized anxiety disorder in adulthood (ages 19-26), measured by the DISC. Models control for race, socioeconomic status, gender, intervention status, earlier depressive symptoms, anxious mood, aggressive behavior, neighborhood disadvantage, community violence, and alcohol and tobacco use.
Results: Rates of major depressive disorder or generalized anxiety disorder are highest among those who initiated marijuana before age 15 (14.9%), compared to those who initiated at age 15 or older (8.2%) and those who did not use marijuana (1.5%). After adjusting for confounders, youth who began marijuana use in early adolescence (before age 15) are significantly more likely than those who initiated later (ages 15+, aOR=2.9, p=.009) and those who did not use at all (aOR=22.7, p=.004) to meet criteria for past year major depressive disorder and/or generalized anxiety disorder in young adulthood.
Conclusion: Results suggest that early onset marijuana use may make an individual more vulnerable to the development of depression and anxiety, potentially because early marijuana users may not develop appropriate coping skills for dealing with stressors. Future research should directly test this mechanism and consider intervening with marijuana users early in adolescence to facilitate the development of coping skills that may reduce later internalizing problems and negative sequelae.