Trends before and after legalization and COVID-19 on cannabis use among gay, bisexual, and other men who have sex with men in Montreal, Toronto, and Vancouver, Canada: A prospective cohort study.

Chan D.; Wang L.; Barath J.; Gormezano A.; Sparling S.; Lachowsky N.; Hart T.; Cox J.; Tan D.; Grace D. et al. · Canadian journal of public health = Revue canadienne de sante publique · 2026

**Background & Methods** This prospective cohort study examined cannabis use trends among sexually active gay, bisexual, and other men who have sex with men (GBM) aged ≥16 years across three Canadian cities (Montreal n=950, Toronto n=258, Vancouver n=387). Participants completed surveys every 6-12 months from February 2017 through August 2022, with observation periods stratified around cannabis legalization (October 2018) and the COVID-19 pandemic (March 2020 onward). Outcomes included past 6-month any cannabis use, frequency of use, and high-risk use (ASSIST scores ≥27) analyzed using multivariable generalized linear mixed models. **Key Findings** - No significant changes in past 6-month cannabis use occurred immediately following legalization (November 2018-March 2020), but declines were observed post-COVID-19 (June 2020 onward; OR=0.81, 95% CI 0.66-1.00). - Frequency of cannabis consumption showed no significant trends across any study period, suggesting that among users, consumption patterns remained stable despite legalization and pandemic-related disruptions. - High-risk cannabis use was strongly associated with mental health comorbidities: moderate/severe anxiety (AOR=2.94, 95% CI 1.60-5.39), moderate/severe depression (AOR=2.55, 95% CI 1.26-5.17), depression diagnosis (AOR=2.42, 95% CI 1.29-4.57), and hazardous alcohol use (AUDIT-C ≥4; AOR=1.69, 95% CI 1.00-2.87). High-risk use was not associated with study visits in either post-legalization or post-COVID periods. **Dosage & Administration** Not reported. **Safety & Adverse Effects** Not reported. The study did not assess direct adverse effects of cannabis use; however, high-risk cannabis use was identified as a marker associated with concurrent mental health conditions including anxiety, depression, and problematic alcohol consumption. **Evidence Quality** This prospective cohort study provides moderate evidence. Strengths include longitudinal design, multi-city recruitment, and standardized validated screening tools (ASSIST, AUDIT-C). Limitations include potential selection bias (urban GBM only), incomplete follow-up data across the study period, and the inability to establish causality between cannabis use and mental health outcomes. The relatively small Toronto sample may limit generalizability for that city.

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