An interrupted time series evaluation of the effect of cannabis legalization on intentional self-harm in two Canadian provinces: Ontario and Alberta.

Introduction: Despite the association between cannabis use and higher prevalence of suicidal ideation and attempt, the effect of cannabis legalization and regulation in Canada on intentional self-harm has not been determined.

Methods: We used an interrupted time series of population-based rates of emergency department (ED) visits and hospitalizations for intentional self-harm per 100 000 in Ontario and Alberta from January/April 2010 to February 2020. Aggregate monthly counts of ED visits and hospitalizations for intentional self-harm (ICD-10 codes X60-X84, R45.8) were obtained from the National Ambulatory Care Reporting System and Discharge Abstract Database, respectively.

Results: The legalization and regulation of cannabis in Canada was not significantly associated with a change in rates of ED visits for intentional self-harm in Ontario (level = 0.58, 95% CI: -1.14 to 2.31; trend = -0.17, 95% CI: -0.35 to 0.01) or Alberta (level = -0.06, 95% CI: -2.25 to 2.12; trend = -0.07, 95% CI: -0.27 to 0.13). Hospitalizations for intentional self-harm also remained unchanged in Ontario (level = -0.14, 95% CI: -0.48 to 0.20; trend = 0.01, 95% CI: -0.03 to 0.04) and Alberta (level = -0.41, 95% CI: -1.03 to 0.21; trend = -0.03, 95% CI: -0.08 to 0.03).

Conclusion: Legalization and regulation of cannabis in Canada has not increased rates of ED visits or hospitalizations for intentional self-harm in Ontario and Alberta. Individual-level analyses that account for demographic characteristics and include other provinces and territories are needed.