Equity-Related Determinants of Frequent Emergency Department Visits for Substance Use Disorders: A Population-Based Study in Ontario, Canada

Background: Substance use disorders (SUDs) represent a growing public health concern in Canada, contributing to emergency department (ED) overcrowding and high system costs. Despite rising rates of SUD-related ED visits, the role of equity-related determinants, such as socioeconomic status, households and dwellings marginalization, and access to coordinated care, remains insufficiently understood. Aim: This study examined how equity-related and sociodemographic factors, along with clinical and service utilization characteristics, are associated with frequent ED visits for SUD in Ontario, Canada. Methods: Using provincial health administrative data from ICES, we conducted a retrospective cohort analysis of individuals aged 12 and older with an SUD-related ED visit between April 2022 and March 2023. Frequent ED visits were defined as three or more substance use–related emergency department visits in the 12 months preceding an individual’s index visit, excluding the index visit itself, which represented approximately the 90th percentile of visit frequency in the cohort. Logistic regression identified factors associated with frequent ED utilization (⩾3 annually). Results: Frequent SUD-related ED visitors were disproportionately young adults (25–44 years) and male. Individuals in the most housing-unstable areas had significantly higher odds of frequent ED visits. Racialized and newcomer indices were not statistically associated with frequent visits. Comorbid mental illness, chronic diseases, and alcohol use were strong clinical correlates. High service utilization patterns, including prior mental health and acute care hospitalizations, were also associated with frequent ED use. Conclusion: High-frequency ED users with SUD reflect a convergence of clinical complexity, socioeconomic vulnerability, and systemic gaps. While households and dwellings marginalization emerged as a key factor, the absence of associations with racialized or newcomer indices should not be misread as a lack of need, as these indices were measured at the area level. These findings highlight the urgent need for equity-informed, integrated care to reduce preventable ED use.