In a 5-year prospective study of 1,428 Canadian adults, cannabis use frequency increased modestly (1.75% more days over 5 years) while cannabis misuse scores decreased, with frequent pre-legalization users showing the largest reductions in both use and misuse.
Policymakers evaluating legalization outcomes and anyone interested in the real-world effects of cannabis legalization.
Misuse decreased even as use frequency increased over 5 years
What the researchers found
Cannabis use frequency increased by 0.35% of days per year overall (1.75% over 5 years). CUDIT-R misuse scores decreased by 0.08 points per year (0.4 over 5 years). Critically, pre-legalization frequent consumers showed the largest decreases in both use and misuse, while occasional users and nonusers showed modest increases. Product preferences shifted from dried flower toward edibles, liquids, and vape pens.
Why it matters
This is among the first longitudinal studies to track the same individuals through cannabis legalization. The finding that misuse decreased even as use increased, and that frequent users improved the most, provides the most nuanced picture yet of legalization's within-person effects.
The numbers in context
N = 1,428. 60.2% female. Mean age 34.5. 11 waves, 90% retention. Use: +0.35% of days/year. CUDIT-R: -0.08/year (scale 0-32). Frequent pre-legalization users: largest decreases. Nonusers: modest increases. Product shift: away from flower toward edibles and vape.
How the study worked
Prospective cohort study with up to 11 biannual assessments from September 2018 to October 2023 in Ontario, Canada. 1,428 community-dwelling adults aged 18-65. Mean 90% retention across all waves. Linear mixed-effects modeling assessed changes in cannabis use frequency and CUDIT-R scores.
What this study cannot tell us
Ontario-specific population. Self-reported use and misuse. The COVID-19 pandemic overlapped with the study period, confounding interpretation. Attrition could bias results if those worsening dropped out.
How to read the evidence
Prospective cohort with 90% retention over 5 years and 11 waves. Among the strongest longitudinal evidence on legalization effects. Published in JAMA Network Open.
When this study was published
Published in 2025 in JAMA Network Open with data through 2023.
The bigger picture
The decrease in misuse among frequent users may reflect the normalization and regulation of cannabis removing some of the risk-taking behavior associated with illegal use. The product diversification (from flower to edibles) aligns with a market maturation that could have both positive (less smoking) and negative (delayed onset risks) public health implications.
Questions still open
- Will the misuse decrease continue beyond 5 years? Is the product shift toward edibles a net positive or negative for public health?
Common questions
Did legalization make cannabis use worse?
Why did frequent users improve the most?
Read the original research
Cannabis Use and Misuse Following Recreational Cannabis Legalization.
JAMA network open, 8(4), e256551
Citation
McDonald, André J; Doggett, Amanda; Belisario, Kyla; Gillard, Jessica; De Jesus, Jane; Vandehei, Emily; Lee, Laura; Halladay, Jillian; MacKillop, James. (2025). Cannabis Use and Misuse Following Recreational Cannabis Legalization.. JAMA network open, 8(4), e256551. https://doi.org/10.1001/jamanetworkopen.2025.6551