Transitions in the use of multiple substances from adolescence to young adulthood

Background: Research indicates that many adolescents frequently use multiple substances. This study examines stability and transitions in the use and co-use of multiple substances (cigarette, alcohol, marijuana, illicit drugs) from adolescence to young adulthood. Methods: Data were collected biennially from 662 youth in six assessments across ten years (2003-2013). We used latent class analysis (LCA) to classify youth by substances used at each wave and used latent transition analysis (LTA) to examine transition probabilities across waves. Results: At each wave, a three-class model best fit the data. Classes included a poly-use class, that had the highest probabilities of use among all substances, a co-use class, that had high probabilities of use of alcohol and marijuana, and 'an alcohol-dominate class that started with low probabilities of use among all substances but showed increasing probabilities of alcohol use, at later ages. LTA showed that the probability of remaining in the poly-use class was the most stable from one wave to the next, followed by the alcohol-dominate class, and the co-use class. The most transitions occurred for the co-use class, with more individuals transitioning to the poly-use class than to the alcohol-dominate class. Conclusions: Strong stability among adolescent substance use classes was found between waves. Transitions were typically to classes using more substances, although, transitions to use fewer substances was evident for some individuals. Distinguishing stable and transitioning classes of substance use and co-use provides opportunities for prevention and intervention to disrupt high-risk use classes.