Simultaneous Trajectories of Alcohol and Cannabis Use From Adolescence to Emerging Adulthood: Associations With Role Transitions and Functional Outcomes

Alcohol and cannabis are the most widely used substances among young people. This study identifies alcohol and cannabis (AC) trajectory classes, and examines class differences on adult role transitions and functioning during emerging adulthood. Participants (n = 3,265) completed six annual surveys (ages 16 to 22) on frequency of past month alcohol and cannabis use. Parallel process growth mixture models (PP-GMM) were used to model simultaneous trajectories of use and identify latent trajectory classes based on AC co-use. Trajectory classes were compared on age 23 outcomes. Analyses identified four trajectory classes of co-use: Initial AC Abstainer with Increasing AC Use (85%); Initial Low AC Use with Increasing Drinking (5%); Increasing Cannabis Use with Steady Drinking (3%); and Decreasing Cannabis Use with Steady Drinking (7%). The two trajectory classes with early AC co-use were less likely to have made certain role transitions, and reported poorer functioning in emerging adulthood, but in distinct ways. For example, the Decreasing Cannabis Use with Steady Drinking class was less likely to graduate from college, and reported more AC consequences and related problems, whereas the Initial Low AC Use with Increasing Drinking class was less likely to be employed full-time, and reported poorer mental health. The Increasing Cannabis Use with Steady Drinking class tended to fall between the Initial AC Abstainer class and the two early AC co-use trajectory classes on outcomes. Results indicate the ways in which AC co-use can affect functional outcomes and the timing of role transitions during the transition to young adulthood.