Background: Although Medicaid expansion under the Affordable Care Act reduces uninsurance, little evidence exists on its impact on mental health and substance use (MHSU) related healthcare utilization. Therefore, the objectives of this study are to examine the impact of Medicaid expansion on emergency department visits related to mental health and substance use disorders and to examine its effect on the variation in payer mix. Methods: The study utilizes state-level quarterly emergency department (ED) visit data from Healthcare Cost and Utilization Project's Fast Stats Database, along with state socio-demographic and health policy data for the analysis. A difference-in-differences regression analysis approach was utilized in comparing MHSU-related ED visit data between expansion and non-expansion states from 2006 to 2019 for all visits and by payer mix. Results: Medicaid expansion was associated with additional 0.35 non-Medicare adult MHSU-related ED visits per 1,000 population (p < 0.05) in expansion states compared with non-expansion states. In addition, Medicaid expansion was associated with about 20.4% increase (p < 0.01) in Medicaid-share of MHSU-related ED visits, about 17.4% reduction (p < 0.01) in uninsured-share of MHSU-related ED visits, and about 3% reduction (p < 0.05) in privately-insured share of MHSU-related ED visits in expansion states compared with non-expansion states. Conclusions: The findings indicate that Medicaid expansion was associated with increased MHSU-related ED visits among the Medicaid population and the overall non-Medicare adult population, while it was associated with reductions in MHSU-related ED visits among the uninsured and privately-insured populations in expansion states compared with non-expansion states.
Keywords: Medicaid expansion; emergency department; mental health; substance use.