Knowledge about the health effects of cannabis before and after legalization of 'recreational' cannabis in Canada: findings from the International Cannabis Policy Study, 2018-2024.

Abstract

Background: Although prior research has examined how cannabis legal status relates to psychosocial predictors of use, less is known about whether recreational legalization influences public knowledge of specific cannabis-related health effects. 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, significant decreases were observed for harms during pregnancy or breastfeeding (p < .001), danger while driving or operating machinery (p = 0.015), risk of psychosis and schizophrenia (p = 0.003), and risk of diabetes (p = 0.001).

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 remained, particularly among frequent consumers.