Youth Cannabis Use Slightly Decreased After Legalization in Canada, But Risk Factor Profiles Changed
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.
Quick Facts
What This Study 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.
Key Numbers
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 They Did This
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).
Why This Research 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 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.
What This Study Doesn't 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.
Questions This Raises
- ?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?
Trust & Context
- Key Stat:
- Youth cannabis use dropped from 15% to 12.3% after legalization
- Evidence Grade:
- Large school-based sample spanning a natural policy experiment with novel analytical approach. Pandemic confounding is a significant limitation.
- Study Age:
- 2025 study comparing 2017-18 (pre-legalization) and 2021-22 (post-legalization) data.
- Original Title:
- Using decision trees to examine risk profiles for cannabis use among large samples of underage youth before and after cannabis legalization in Canada.
- Published In:
- Addictive behaviors reports, 22, 100632 (2025)
- Authors:
- Leatherdale, Scott T(10), Battista, Katelyn(2), Patte, Karen A(4), MacKillop, James, Bélanger, Richard
- Database ID:
- RTHC-06907
Evidence Hierarchy
Follows a group of people over time to track how outcomes develop.
What do these levels mean? →Frequently Asked Questions
Did legalization increase youth cannabis use?
No. In this study of 85 Canadian schools, underage cannabis use slightly decreased from 15% to 12.3% in the four years after legalization.
What predicts youth cannabis use?
Low value on academic grades was the top risk factor in both periods. After legalization, anxiety and skipping breakfast emerged as new predictors.
Read More on RethinkTHC
Cite This Study
https://rethinkthc.com/research/RTHC-06907APA
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
MLA
Leatherdale, Scott T, et al. "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, 2025. https://doi.org/10.1016/j.abrep.2025.100632
RethinkTHC
RethinkTHC Research Database. "Using decision trees to examine risk profiles for cannabis u..." RTHC-06907. Retrieved from https://rethinkthc.com/research/leatherdale-2025-using-decision-trees-to
Access the Original Study
Study data sourced from PubMed, a service of the U.S. National Library of Medicine, National Institutes of Health.
This study breakdown was produced by the RethinkTHC research team. We analyze and report published research findings without making health recommendations. All interpretations are based solely on the published abstract and study data.