Developmental Trajectories of Tobacco/Nicotine and Cannabis Use and Patterns of Product Co-use in Young Adulthood.

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Introduction:Concurrent co-use of tobacco/nicotine and cannabis (T/C) products is common among young people and may increase risks for negative health and psychosocial outcomes, but little is known about developmental patterns of T/C co-use. This study aimed to identify distinct trajectory classes of concurrent T/C co-use from ages 16 to 21 and compare groups on T/C co-use behaviors in young adulthood.Methods:Participants (n = 2497) reported T/C use on annual online surveys from 2015 to 2019 (ages 16-22). We used parallel process growth mixture models to model simultaneous trajectories of past-month cigarette, e-cigarette, smokeless tobacco, and cannabis use and identify latent classes of T/C trajectories. Classes were then compared on types and number of T/C products used and types of T/C co-use in young adulthood.Results:Models revealed 4 T/C classes: Low/No T/C Use, Early Concurrent T/C Co-use, Late Concurrent T/C Co-use, and Tobacco Quitters/Cannabis Maintainers. Compared to other classes, the Early Concurrent T/C Co-use group—individuals with rapid progression to concurrent T/C co-use during adolescence—were more likely to report poly-tobacco use, poly-cannabis use, same-occasion sequential T/C co-use and T/C co-administration (ie, mixing T/C) of both combustible and vaping products in young adulthood.Conclusion:Early progression to concurrent T/C co-use in adolescence is prospectively linked to poly-product use and co-use of T/C products in young adulthood. Prevention efforts targeting co-use of T/C products in adolescence may help to reduce riskier patterns of T/C use and co-use in young adulthood.