Longitudinal trajectories of marijuana use from adolescence to young adulthood.

BACKGROUND: Marijuana use is increasingly widespread among adolescents and young adults; however, few studies have examined longitudinal trajectories of marijuana use during this important developmental period. As such, we examined adolescent trajectories of marijuana use and the psychosocial factors that may differentiate individuals who escalate their marijuana use over adolescence and young adulthood from those who do not.

METHODS: Participants were 1204 9th and 10th graders at baseline who were over-sampled for cigarette use and were followed over 6-years, as part of an extensive longitudinal study, the Social and Emotional Contexts of Adolescent Smoking Patterns (SECASP) study. Growth Mixture Modeling (GMM) was used to model trajectories of marijuana use and Mixed Effects Regression analyses were used to examine psychosocial correlates of marijuana use escalation over time.

RESULTS: Our results revealed three trajectories of non-escalating users (low users, medium users, and high users) and one escalating user trajectory. We found that relative to Non-escalators the Escalators had higher cigarette smoking (p<.0001), novelty-seeking (p=.02), aggressive and anti-social behavior (p<.007), and problem behavior related to peer context (p=.04). Moreover, there were important time and Group by Time interactions in some of these relationships. On the other hand, parental control and depression did not differ between escalators and low and medium non-escalating users.

CONCLUSIONS: Cigarette smoking, novelty-seeking, aggressive and anti-social behavior, and peer influence are related to 'escalating' marijuana use throughout adolescence and young adulthood.