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

This study offers a model for using multidimensional growth mixture models to identify polysubstance use trajectories by examining transitions among conjoint substance use trajectories from adolescence to young adulthood and exploring potential moderators that may facilitate transitions towards healthier substance use trajectories in young adulthood. Longitudinal mixture modeling was used to examine six waves of data collected during adolescence (ages 13, 14, 15) and young adulthood (ages 25, 29, 31) in 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 substance use 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 substance use 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%). The transition from adolescence to young adulthood showed the strongest continuity in the poly-use class and the weakest in the low use class, with a general trend toward adding substances rather than reducing them. College graduation moderated the transition in substance use patterns from adolescence to young adulthood for low use and alcohol dominant adolescent classes but not for the poly-use class. Delays in adult role assumptions were not consistently associated with substance use classes during this transition. However, where significant, delayed marriage and parenthood acted as protective factors against the progression of substance use leading into young adulthood. The findings underscore the need for early detection and tailored prevention efforts among adolescents. By identifying pivotal periods and specific substance use patterns, these findings inform the timing and focus of targeted interventions designed to reduce the escalation of substance use leading into young adulthood.