Cannabis and Antidepressant Use During the Periods Before and After Cannabis Legalization in Ontario, Canada: 2013 to 2023

Background: Despite the gradual shift in public policy and perception toward cannabis use, there is limited evidence on the co-use of cannabis and antidepressants, and comparative use of these substances across the 3 distinct phases of cannabis legalization. We examined the use of cannabis and/or antidepressant patterns over time, and explored potential sex differences over legalization phases. Methods: Data were utilized from the 2013 to 2023 Centre for Addiction and Mental Health (CAMH) Monitor study, a repeated cross-sectional survey of adults 18 years of age and older (n = 20 498; 52% female). The surveys employed a regionally stratified sampling design using computer-assisted telephone interviews and web surveys. Multinomial logistic regression modeling was performed to analyze the data. Results: The exclusive use of cannabis increased from 7.2% to 14.9%, and use of both cannabis and antidepressant increased from 1.3% to 5.5% between pre-and post-legalization of cannabis periods, respectively ( P < .001). There was a significant interaction between legalization periods and sex on the use of cannabis and/or antidepressant ( P < .001), suggesting that the relative risk ratio (RRR) of using cannabis rather than antidepressant was higher among females during the post-legalization period, compared to the pre-legalization period (RRR = 2.27, 95% confidence interval: 1.76-2.93). In both sexes, the relative risk of using both substances was significantly higher during the post-legalization period. Conclusions: As cannabis becomes legal and commercialized, the likelihood of using it over antidepressants seems to increase, especially among females. The growing trend of using both substances could have significant public health and clinical implications due to the potential for harmful drug interactions.