Youth Cannabis Use in Canada Declines After Legalization, Though Risk Factors Changed, Study Shows

Has the use of cannabis among underage youth in Canada changed since non-medical cannabis was legalized in October 2018? Using a statistical model approach, researchers compared risk profiles in the school years before legalization (2017–2018) and in years after (2021–2022) in order to gauge the effect on youth use of cannabis. The aim was to fill in literature gaps by examining the behavioral and psychosocial factors that influence youth use of cannabis.

Cannabis use Among Youth in Canada

Compared to most other countries, youth cannabis use is higher in Canada, the study noted, though one year after legalization, no significant changes in trends were seen in the short term. The COVID-19 pandemic complicated studies in later years, though generally showed a decline. This study focused on comparing the risk factors and changes in the behavioral drivers that lead to youth cannabis use. Ultimately, the results of this research indicated that use of cannabis declined among youth in the years following legalization, though the risk factors changed over time. The study, “Using decision trees to examine risk profiles for cannabis use among large samples of underage youth before and after cannabis legalization in Canada,” was published online in Addictive Behavior Reports in October 2025.

Study Design: Data Comparison

Data from the ongoing prospective cohort study COMPASS (2012–2027) was used in this study, involving 85 secondary schools in six provinces. This study examined cannabis use frequency as an outcome measure, along with 31 other variables. The data samples were divided into two time periods: 2017–2018 (pre-legalization, T₁) and 2021–2022 (post-legalization, T₂). T₁ included 38,885 participants, and T₂ involved 29,619 participants.

Based on responses to the cannabis use frequency question (“In the last 12 months, how often did you use marijuana or cannabis? [a joint, pot, weed, hash]?”), students who used cannabis at least once per month were considered current users.

Prior studies identified truancy, academic performance, bullying, and peer influence as associated with cannabis use among youth in the years before legalization. Additionally, screen time, sleep, the use of other substances, and psychosocial wellbeing were also identified as risk factors.

Results: Decrease in Youth Cannabis Use

Overall, the percentage of youth cannabis use in Canada in the years after legalization decreased. Highlighted results include:

• At T₁, 15.0 % of students reported current cannabis use, compared to 12.3 % of students at T₂
• Six main risk profiles were identified in T₁, including placing a lower value on good grades, spending less time doing homework, and spending at least 45 minutes per day texting
• The highest risk group in T₁ comprised 30.4% of the sample
• In the T₂ group, 11 risk profiles, including depression and having elevated anxiety, placing a lower value on good grades, and not eating breakfast daily
• The highest risk group in T₂ comprised 18.8% of the sample

Those who responded that they had never used cannabis increased after legalization, and a slight decrease in current cannabis use was also seen.

The researchers noted the large, population-based sample size as a strength of the study. Limitations to the study include the possibility of a convenience sample due to the COMPASS study including only schools willing to participate, and the lack of survey questions on peer or parental use of cannabis, which are considered significant risk factors.

Impact on Youth Intervention Programs

The results indicate that there is a need to identify the risk factors for youth cannabis use, and create early, tailored intervention programs. “This study provides evidence that, in a relatively short 4-year period spanning the cannabis pre-legalization to post-legalization time periods, adolescent cannabis use has declined, but the risk factor profile for cannabis use has substantively changed, increasingly implicating elevations in internalizing mental health conditions,” the researchers concluded. Looking toward the future of early intervention programs should involve relevant and timely efforts, they add.

Reference

1. Leatherdale, ST.; Battista, K.; Patte, KA.; MacKillop, J.; Bélanger, R. 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, 22. DOI: 10.1016/j.abrep.2025.100632