A study of 85 Canadian secondary schools found past-month cannabis use among underage youth decreased from 15% to 12.3% after legalization, but the risk factor profiles shifted, with anxiety and breakfast-skipping emerging as new predictors alongside the consistent factor of low academic motivation.
Youth prevention researchers, school health officials, and policymakers evaluating legalization impacts on minors.
Youth cannabis use dropped from 15% to 12.3% after legalization
What the researchers found
Current cannabis use dropped from 15.0% (pre-legalization 2017-18) to 12.3% (post-legalization 2021-22). Pre-legalization highest risk group (27% probability): students who devalued grades + texted 45+ min/day (30.4% of sample). Post-legalization highest risk group (27% probability): students who devalued grades + skipped breakfast + had elevated anxiety (18.8% of sample). Risk factor rankings changed considerably between periods.
Why it matters
Counter to fears, underage cannabis use did not increase after legalization. However, the changing risk profiles mean prevention programs must adapt to target emerging risk factors like anxiety rather than relying on pre-legalization approaches.
The numbers in context
85 schools; 15.0% use pre-legalization vs. 12.3% post; 6 risk profiles pre vs. 11 post; top risk factor consistent: low value on grades; new post-legalization factors: anxiety, skipping breakfast.
How the study worked
COMPASS Study data from 85 secondary schools at two timepoints. Classification tree analysis modeling interactions among multiple risk factors. Wave 1 (2017-18, medical-only policy) and wave 2 (2021-22, adult-use policy).
What this study cannot tell us
Cannot separate legalization effects from pandemic effects (2021-22 data). School-based sample excludes non-enrolled youth. Classification trees may overfit. Self-reported cannabis use.
How to read the evidence
Large school-based sample spanning a natural policy experiment with novel analytical approach. Pandemic confounding is a significant limitation.
When this study was published
2025 study comparing 2017-18 (pre-legalization) and 2021-22 (post-legalization) data.
The bigger picture
Cannabis legalization did not create the youth use epidemic that was feared. But the shift in risk factors suggests the social and psychological context of youth cannabis use is evolving, possibly influenced by pandemic effects during the study period.
Questions still open
- How much of the risk factor shift is due to legalization vs. the pandemic?
- Should prevention programs now target anxiety reduction to prevent cannabis use?
Common questions
Did legalization increase youth cannabis use?
What predicts youth cannabis use?
Read the original research
Using decision trees to examine risk profiles for cannabis use among large samples of underage youth before and after cannabis legalization in Canada.
Addictive behaviors reports, 22, 100632
Citation
Leatherdale, Scott T; Battista, Katelyn; Patte, Karen A; MacKillop, James; Bélanger, Richard. (2025). Using decision trees to examine risk profiles for cannabis use among large samples of underage youth before and after cannabis legalization in Canada.. Addictive behaviors reports, 22, 100632. https://doi.org/10.1016/j.abrep.2025.100632
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