Changing Developmental Patterns of Cannabis and Alcohol Use in Washington State: an Analysis of Young Adult Birth Cohorts Born in 1990-2004.

Alcohol and cannabis are the two most commonly used substances in young adulthood. Prior evidence shows that while risky alcohol use peaks in the mid-20 s and decreases by the end of young adulthood (i.e., "maturing out"), cannabis use prevalence decreases gradually across young adulthood. As the landscape of cannabis legalization in the USA evolves, it is critical to assess changes in young adult patterns of use. This study examined developmental patterns of young adult cannabis and alcohol use in Washington State (WA). Annual repeated cross-sectional survey data from 2015 to 2022 were collected from 15,371 young adults 18-25 living in WA. Logistic regression models examined changes in alcohol (any past month use, frequent use, heavy episodic drinking [HED]) and cannabis (any past month use, frequent use) by developmental age and birth cohort. Cannabis use prevalence was higher at age 21-22 compared to age 18-20, a departure from prior studies. In more recent birth cohorts, prevalence among 23-25-year-olds was lower than among 21-22-year-olds, suggesting an emerging pattern of maturing out. Additionally, there was a significant moderation of developmental patterns of risky (HED and frequent) alcohol use by birth cohort. As cannabis legalization continues to evolve, it is critical for programs to prioritize early prevention prior to and at age 21 to mitigate and prevent associated adverse health outcomes of cannabis use. Continued surveillance including older age groups is needed to characterize changing developmental patterns of young adult cannabis use.