Knowledge about the health effects of cannabis before and after ‘recreational’ cannabis legalization in Canada: Findings from the International Cannabis Policy Study, 2018 – 2024

Background To date, few studies have examined the impact of legalization on important psychosocial predictors of cannabis consumption, including risk perceptions. This study addresses this gap by analyzing trends in knowledge of health effects of cannabis consumption following the legalization of recreational cannabis in Canada. Methods Data were collected from repeated cross-sectional national surveys conducted in the year prior to legalization of ‘recreational’ cannabis in Canada (2018), and five years post-legalization (2019–2023) among 93,933 respondents aged 16–65. Regression models examined differences pre vs. post-legalization in health knowledge, assessed as agreement with each of 7 health effects from cannabis and a composite Health Knowledge Index, adjusting for cannabis consumption, mental health history, and sociodemographics. Results Across all years, agreement was highest for the risks of impaired driving (79–81%) and lowest for psychosis and schizophrenia risk (34–38%). Health knowledge was highest among non-consumers, those without mental illness history, and youth aged 16–25 (p < .001, all contrasts). No changes were observed in the Health Knowledge Index pre vs post-legalization; however, modest increases were observed for harms during pregnancy or breastfeeding (p < .001), cannabis addiction (p < .001), risk of psychosis and schizophrenia (p < .001), and teen consumption (p < .001). Conclusions Overall, only modest differences in knowledge of cannabis health effects were observed in the 5 years following cannabis legalization in Canada; however, persistent gaps in health knowledge persisted, particularly among frequent consumers.