Background: Municipal bans on cannabis retailers may influence healthcare utilization by restricting cannabis availability. Understanding their spatial impact on cannabis-related emergency department (ED) visits is essential for evidence-based policymaking and health geography research. Objective: To assess whether municipal bans on cannabis retail stores reduced cannabis-related ED visits in Ontario, Canada, with a focus on spatial disparities in healthcare access and utilization. Methods: This quasi-experimental study used a double robust difference-in-differences design with inverse probability weighting. We analyzed municipal-level quarterly data (2016-2023) from health administrative records, covering all Ontario residents eligible for Ontario Health Insurance Plan (n=12,079,699). The primary outcome was the incidence rate of cannabis-related ED visits per 100,000 individuals per quarter. Secondary analyses examined cannabis-induced psychosis and opioid-related ED visits. Results: Municipalities that banned cannabis retailers experienced a statistically significant reduction of 3.23 (95% CI: -6.21 to -0.25) cannabis-related ED visits per 100,000 individuals per quarter compared to municipalities with cannabis stores. Sensitivity analyses confirmed the robustness of these findings. No significant changes were observed for cannabis-induced psychosis or opioid-related ED visits. The findings highlight spatial inequalities in cannabis-related healthcare utilization based on local policy decisions. Conclusions: Municipal bans on cannabis retail stores modestly reduced cannabis-related ED visits, suggesting that restricting physical access to cannabis may alleviate emergency service burdens. However, the modest effect size likely reflects ongoing cannabis availability through online sales and cross-municipal travel. These findings underscore the importance of considering spatial dimensions of cannabis access, healthcare utilization, and policy impact in health geography. Complementary harm reduction strategies, such as public education and regulatory oversight of online sales, are needed to mitigate cannabis-related health outcomes effectively.