Abstract
IMPORTANCE: In January 2020, Quebec raised the minimum legal age (MLA) for cannabis from 18 to 21 years. Evidence is needed to inform the ongoing debate on this policy. Although proponents believe that a higher MLA will protect youths from the harms of cannabis use, critics argue that it will push them back to the illegal market. OBJECTIVE: To investigate changes in youth cannabis use after an increase in MLA for cannabis in Quebec. DESIGN, SETTING, AND PARTICIPANTS: This cross-sectional study with difference-in-differences analysis compared changes in cannabis use among youths aged 15 to 20 years in Quebec vs all other Canadian provinces before and after Quebec's increase in MLA. All estimates in descriptive and regression analyses were weighted. Nationally representative data from the National Cannabis Surveys 2018-2020 were used. INTERVENTION: Increase in MLA for cannabis in Quebec implemented in January 2020. MAIN OUTCOMES AND MEASURES: Past-3-month cannabis use. RESULTS: The study sample included 1005 respondents (mean [SD] age, 17.5 [1.7] years; 50.2% [SD, 50.0%] male). After policy implementation, the increase in past-3-month cannabis use among youths aged 18 to 20 was 16.4 percentage points (95% CI, -27.3 to -5.5 percentage points; P = .01), or 51%, lower in Quebec than in other provinces. Meanwhile, no significant change in cannabis use among youths aged 15 to 17 years was found. The results were robust to several checks, including accounting for possible confounding effects of the COVID-19 pandemic on cannabis use. CONCLUSIONS AND RELEVANCE: In this study, an increase in the MLA from 18 to 21 years in Quebec was associated with a significantly lower increase in cannabis use among youths aged 18 to 20 years but no change in cannabis use among those aged 15 to 17 years. These findings can help to alleviate concerns that youths would switch to illegal markets in response to a higher MLA.