Introduction: Non-medical cannabis recently became legal on October 18th, 2018 to Canadian adults. The impact of legalization on Emergency Departments (EDs) has been identified as a major concern. The study objective was to identify changes in cannabis-related ED visits and changes in co-existing diagnoses associated with cannabis-related ED visits pre- and post-legalization for the entire urban population of Alberta. Urban Alberta was defined as Calgary and Edmonton, inclusive of Sherwood Park and St. Albert given the proximity of some Edmontonians to their EDs) encompassing 12 adult EDs and 2 pediatric EDs. Methods: Retrospective data was collected from the National Ambulatory Care Reporting System, and from the HealthLink and the Alberta Poison and Drug Information Service (PADIS) public telehealth call databases. An interrupted time-series analysis was completed via segmented regression calculation in addition to incident rate and relative risk ratio calculation for the pre- and post-legalization periods to identify both differences among the entire urban Alberta population and differences among individuals presenting to the ED. Data was collected from October 1st, 2013 up to July 31st, 2019 for ED visits and was adjusted for natural population increase using quarterly reports from the Government of Alberta. Results: The sample included 11 770 pre-legalization cannabis-related visits, and 2962 post-legalization visits. Volumes of ED visits for cannabis-related harms were found to increase post-legalization within urban EDs (IRR 1.45, 95% CI 1.39, 1.51; absolute level change: 43.48 visits per month in urban Alberta, 95% CI 26.52, 60.43), and for PADIS calls (IRR 1.87, 95% CI 1.55, 2.37; absolute level change: 4.02 calls per month in Alberta, 95% CI 0.11, 7.94). The increase in visits to EDs equates to an increase of 2.72 visits per month, per ED. Lastly, increases were observed for cannabinoid hyperemesis (RR 1.23, 95% CI 1.10, 1.36), unintentional ingestion (RR 1.48, 95% CI 1.34, 1.62), and in individuals leaving the ED pre-treatment (RR 1.28, 95% CI 1.08, 1.49). Decreases were observed for coingestant use (RR 0.77, 95% CI 0.73, 0.81) and hospital admissions (RR 0.88, 95% CI 0.80, 0.96). Conclusion: Overall, national legalization of cannabis appears to be correlated with a small increase in cannabis-related ED visits and poison control calls. Post-legalization, fewer patients are being admitted, though cannabinoid hyperemesis appears to be on the rise.