Trajectories of Marijuana Use from Adolescence into Adulthood: Environmental and Individual Correlates

In the U.S., marijuana is the most commonly used illicit drug (SAMHSA, 2002). Previous research has commonly focused on timing of onset of marijuana use on comparing users and nonusers; less is known about predictors and consequences of other patterns of use. The present paper examines a) whether distinct trajectories of marijuana use can be identified from ages 14 to 30, and b) what childhood, adolescent, and adult environmental and individual factors distinguish membership in these trajectories.

Marijuana use trajectories were estimated using Growth Mixture Modeling in Mplus from ages 14-30. Participants from the Seattle Social Development Project (N=808) reported general and marijuana-specific functioning of their family, school, peer, neighborhood environments at key points of convergence and divergence of trajectories (ages 10-14, 18, 21, 24). Measures of behavioral disinhibition, depression, anxiety, and substance use were also examined.  Outcome variables included substance abuse and dependence, mental health, problem behavior, economic well-being, and positive functioning at age 33.

Four trajectories of use were identified: Nonusers (27%), Adolescent-limited (21%), Late-onset (20%), and Chronic (32%).

In childhood (ages 10-14), the Chronic and the Adolescent-limited groups were differentiated only by school environment and behavioral disinhibition. The Late-onset group mostly resembled the Nonuser group. However, by age 18 the Chronic group differentiated from the Adolescent-limited on most indicators.  The Late-onset group reported more antisocial peers, substance use, and behavioral disinhibition than the Nonusers. 

At ages 21 and 24, the Adolescent-limited and Late-onset groups were almost indistinguishable whereas the Chronic users continued to show lowest level of functioning.  Nonusers were similar to Adolescent-limited and Late-onset groups on general functioning, but reported less substance use, behavioral disinhibition, and peer marijuana use.

The Late Onset group was more likely to report alcohol and tobacco abuse/dependence symptoms than Nonusers at age 33, but did not differ on the likelihood of marijuana dependence or on economic and positive functioning outcomes. The Adolescent Limited group was less likely to have graduated from high school, to have finished college, or to be constructively engaged than either the Nonuser or the Late-onset groups.

These results suggest that different patterns of marijuana use in adolescence and young adulthood can be distinguished and that they have distinctly different etiologies. Findings demonstrate that there is developmental heterogeneity in the etiology of marijuana use, indicating different interventions for different patterns of marijuana use.