In post-legalization Washington State, cannabis use prevalence peaks at ages 21-22 rather than declining from 18 as in pre-legalization studies, but newer birth cohorts show emerging signs of reduced use by ages 23-25.
Substance use epidemiologists; prevention program designers targeting young adults.
Cannabis use peak shifted from age 18 (pre-legalization) to 21-22 (post-legalization)
What the researchers found
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.
Why it matters
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 numbers in context
15,371 young adults surveyed annually 2015-2022. Cannabis use higher at 21-22 vs 18-20. Recent birth cohorts: lower prevalence at 23-25 vs 21-22 (emerging maturing out). Birth cohort significantly moderated HED and frequent alcohol use patterns.
How the study worked
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).
What this study cannot tell us
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.
How to read the evidence
Moderate: large sample with multiple survey waves and birth cohort analysis, but repeated cross-sectional rather than longitudinal and limited to one state.
When this study was published
2025 study using 2015-2022 data.
The bigger picture
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.
Questions still open
- Will the maturing out pattern strengthen as cannabis legalization stabilizes? Does the shift in peak cannabis use age mirror the legal purchase age in other legalized states?
Common questions
What does "maturing out" mean?
Why does cannabis use peak at 21-22 now?
Read the original research
Changing Developmental Patterns of Cannabis and Alcohol Use in Washington State: an Analysis of Young Adult Birth Cohorts Born in 1990-2004.
Prevention science : the official journal of the Society for Prevention Research, 26(5), 785-797
Citation
Acolin, Jessica; Calhoun, Brian; Rhew, Isaac C; Fleming, Charles B; Hultgren, Brittney; Martinez, Griselda; Kilmer, Jason R; Larimer, Mary; Guttmannova, Katarina. (2025). Changing Developmental Patterns of Cannabis and Alcohol Use in Washington State: an Analysis of Young Adult Birth Cohorts Born in 1990-2004.. Prevention science : the official journal of the Society for Prevention Research, 26(5), 785-797. https://doi.org/10.1007/s11121-025-01813-y
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