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., Competing Interests: MDC is a practising neurosurgeon who treats patients who sustained head injuries or trauma that may have been a result of substance use and intoxication, including due to cannabis. MDC had financial support from the Public Health Agency of Canada for the submitted work. MDC also received a grant from the Canadian Institutes of Health Research for a similar study, which might have an interest in the submitted work (RM and OS were listed as co-applicants). MDC and MW received a research grant from the Toronto Cannabis and Cannabinoid Research Consortium, which might have an interest in the submitted work. MC reports no financial interests, activities, relationships or affiliations that could appear to have influenced the submitted work. Each author confirms that this study has not been previously published in any form and is not currently under consideration by any other journal.