Early adolescent through young adult alcohol and marijuana use trajectories: early predictors, young adult outcomes, and predictive utility.

The present study takes a developmental approach to subgrouping and examines the trajectories of substance use from early adolescence through young adulthood among a community sample of 481 individuals. The patterns of use were examined, subgroups were identified separately for men and women and for alcohol and marijuana, and psychosocial predictors and psychopathology outcomes that differentiated the groups were identified. The results revealed three substantially overlapping subgroups for both alcohol and marijuana: early onset, late onset, and nonuser. Although the general patterns of which dependent variables were related to group were similar for alcohol and marijuana, a closer examination revealed important subgroup differences. For alcohol use, the early-onset group was more dysfunctional in terms of predictors and outcomes whereas the late-onset and nonuser groups were better adjusted. In contrast, for marijuana, the early- and late-onset groups were both more dysfunctional than the nonuser group. In a final analysis, we examined the predictive utility of our developmental approach to subgrouping compared to a traditional, static approach.