Cannabis Use Peaks at Age 21-22 in Washington State, With Signs of "Maturing Out" in Recent Cohorts

Cannabis use prevalence was higher at age 21-22 compared to 18-20, departing from prior pre-legalization research showing gradual decline. In more recent birth cohorts, prevalence among 23-25-year-olds was lower than 21-22-year-olds, suggesting an emerging "maturing out" pattern. Developmental patterns of risky alcohol use (HED, frequent drinking) were significantly moderated by birth cohort.

Annual repeated cross-sectional survey data from 2015-2022 of 15,371 young adults (ages 18-25) in Washington State. Logistic regression examined cannabis and alcohol use by developmental age and birth cohort (born 1990-2004).

Cannabis legalization may have shifted when cannabis use peaks during young adulthood. The finding that peak use now occurs at 21-22 (the legal purchase age) rather than declining from age 18 suggests that legal access timing shapes use trajectories, with implications for when prevention resources should be concentrated.

The concept of "maturing out" -- reducing substance use as adult responsibilities accumulate -- has been well-established for alcohol. This study provides early evidence that a similar pattern may be developing for cannabis use in legalized states, which would have important implications for public health projections.

Repeated cross-sectional design tracks cohort trends but not individual trajectories. Washington State results may not generalize to states with different cannabis policies or demographics. Self-reported data may undercount actual use. The 2015-2022 timeframe captures an evolving post-legalization period.