Trajectories of marijuana use from adolescence into adulthood: Environmental and individual correlates.

This study sought to identify trajectories of marijuana use in the Seattle Social Development Project (n = 808) sample from age 14 through 30, and to examine the extent to which individuals in these trajectories differed in their substance use problems, mental health, problem behavior, economic outcomes, and positive functioning at age 33. In addition, analyses examined between-trajectory differences in family, peer, school, neighborhood, individual, mental health, and substance use factors at key developmental points in adolescence and adulthood. Four trajectories of marijuana use were identified: nonusers (27%), adolescent-limited (21%), late-onset (20%), and chronic (32%) users. At age 33, the chronic trajectory was associated with the worst functioning overall. The late-onset group reported more substance use and sexual risk behavior than nonusers, but was otherwise not differentiated. The adolescent-limited group reported significantly lower educational and economic outcomes at age 33 than the late-onset and nonuser groups. In analyses at earlier ages, adolescent-limited and late-onset groups reported more problems in functioning during the period of escalation in use and improvement in functioning with the beginning of desistance. Implications for prevention are discussed, particularly the unique risks associated with early adolescent versus later onset of marijuana use. (c) 2015 APA, all rights reserved).