Do Classes of Polysubstance Use in Adolescence Differentiate Growth in Substances Used in the Transition to Young Adulthood?

A three-class model fit the data best and included a poly-use class, that had high probabilities of use among all substances, a co-use class, that had high probabilities of use among alcohol and marijuana, and a low-use class that had low probabilities of use among all substances. We then examined trajectories of each substance used by class. Strong continuity of substance use was found by class across 14 years. Additionally, for some substances, higher average levels of use of at age 14 were associated with change in growth of other substances used over time. Conclusions/Importance: Efforts that only target a single drug type may be missing an important opportunity to reduce the use and subsequent consequences related to the use of multiple substances.