Abstract
BACKGROUND: The bidirectional relationship between cannabis use and mental health is complex. With the liberalization of cannabis laws in many countries, it is increasingly important to understand the impacts of cannabis legalization on individuals with mental health conditions. This study aimed to examine changes in cannabis use by mental health status pre-versus 5-years post-legalization of recreational cannabis in Canada. METHODS: Data were from the International Cannabis Policy Study's national repeat cross-sectional surveys, conducted annually in Canada between 2018 and 2023, one year before and five years after the legalization of cannabis. The current analysis includes 92,843 Canadians aged 16-65 years. Adjusted logistic regression models examined changes in daily and past 12-month cannabis use pre-versus post-legalization among individuals experiencing each of the five mental health problems in the last year: anxiety, bipolar, depression, post-traumatic stress disorder (PTSD), and schizophrenia. FINDINGS: Past 12-month cannabis consumption increased from pre-legalization versus the year immediately following legalization (2019) among those with anxiety (adjusted odds ratio (AOR) = 1.33, 95% CI = 1.15, 1.53, p < 0.0001), depression (AOR = 1.47, 95% CI = 1.26, 1.73, p < 0.0001), and those reporting 'no experience' of a mental health problem in the past year (AOR = 1.52, 95% CI = 1.37, 1.68, p < 0.0001). Past 12-month cannabis use remained significantly higher in 2023 versus pre-legalization for anxiety and depression. Daily cannabis use increased from 2018 to 2019 only among those not reporting any experience of a mental health problem in the past year (AOR = 1.34, 95% CI = 1.10, 1.62, p < 0.0001). No other pre-post legalization differences were observed among individuals who experienced bipolar, PTSD, or schizophrenia. INTERPRETATION: Few changes in cannabis use were observed pre-versus post-cannabis legalization among Canadians who reported experiencing a mental health problem, whereas daily and past 12-month use increased among Canadians not reporting a mental health problem. FUNDING: Funding for the ICPS study was provided by a Canadian Institutes of Health Research Project Grant and Project Bridge Grant (PJT-153342).