Cannabis Use Rose Through Age 22 and Stayed Stable in Washington State After Legalization

Cannabis use prevalence increased from ages 18-22 and remained relatively stable through age 26. Ease of access, social norms, and low perceived harm were associated with use, but the strength of these associations varied by age. Injunctive norms (perceptions of use acceptability) and low perceived psychological harm were the most consistent predictors across the full age range.

Repeated cross-sectional data from 15,251 young adults (mean age 22, 68% female) in the Washington Young Adult Health Survey from 2015-2022 (post-legalization). Logistic time-varying effect models examined age-varying associations between risk factors and cannabis use (any and frequent past-month use).

Understanding which risk factors matter most at different ages can help target prevention efforts. The finding that perceived acceptability drives use well into the mid-20s, and that perceived psychological harm becomes more influential with age, suggests that prevention messaging should evolve as young adults mature.

Washington was among the first states to legalize recreational cannabis. This study captures how use patterns develop in a fully legal environment, showing that even with easy access, use peaks in the early 20s and does not continue climbing through the mid-20s.

Repeated cross-sectional design means different individuals were surveyed at different ages, not the same people tracked over time. Washington-specific findings may not apply to states with different legal frameworks. Self-report measures may undercount actual use.