Continuity and Change in Substance Use Patterns During the Transition from Adolescence to Young Adulthood: Examining Changes in Social Roles

To provide a model for using Multidimensional Growth Mixture Models to identify trajectories of polyuse through investigating transitions between conjoint substance use trajectories from adolescence into young adulthood and examining potential moderators that may promote transitions into healthier substance use trajectories in adulthood. Longitudinal mixture modeling of six waves of data in adolescence (ages 13, 14, 15 years) and young adulthood (ages 25, 29, 31 years). Seattle, Washington. Data were drawn from the International Youth Development Study, a longitudinal, cross-national study examining the life course patterns of substance use and development among youth. Participants (N = 961) completed questionnaires on six occasions that assessed demographics (sex, race, highest parent education), suspension and expulsion, individual substance use, partner substance use, and social role transitions (education, marriage, childbearing, employment). Four classes were identified in adolescence and included Low use (n = 572, 59.6%), Alcohol dominant (n = 177, 18.4%), Increasing use (n = 103, 10.7%), and Poly-use (n = 109, 11.3%). Five classes were identified in young adulthood and included Low use (n = 134, 15.3%), Alcohol only (n = 349, 39.8%), Alcohol and Tobacco (n = 97, 11.0%), Alcohol and Cannabis (n = 162, 18.5%), and Poly-use (n = 135, 15.4%).Continuity in substance use patterns in the transition from adolescence to young adulthood was the strongest for the poly-use class and weakest for the low use class, and changes showed a tendency to add substances rather than subtract. Graduating college was a consistent protective factor for young adults. Delays in adult role assumptions were not consistently related to substance use classes. The findings underscore the importance of early detection and prevention among adolescents by informing the timing and focus of targeted interventions aimed at reducing substance use escalation into young adulthood.