Medicaid Expansion and Buprenorphine Dispensing in Early vs Recent Expansion States.

Importance: Patient Protection and Affordable Care Act (ACA) Medicaid expansion has been linked to improved uptake of medications for opioid use disorder (MOUD) access for Medicaid enrollees, but evidence is limited on the associations of post-2018 expansions with population-level treatment. Moreover, prior studies have not implemented modern staggered-adoption estimators or examined outcomes by payer type, risking biased and incomplete inference. Objectives: To evaluate the association of Medicaid expansion with buprenorphine treatment rates (overall and by payer) across all expansion states using updated data and methods and to test whether post-2018 expansions (post-X-waiver and telehealth era) differed from earlier ones. Design, Setting, and Participants: Cross-sectional study of buprenorphine dispensing in participants aged 18 years or older from 2013 to 2024 using the IQVIA Longitudinal Prescription Database containing over 90% of US retail pharmacy claims across 51 US jurisdictions (50 states plus Washington, DC). Cross-sectional difference-in-differences analysis leveraging staggered adoption of changes in monthly buprenorphine MOUD dispensing rates associated with Medicaid expansion. Exposure: Medicaid expansion under the ACA, implemented state-by-state, covering 41 expansion states (plus DC) and 10 nonexpansion states, measured by state and month. Main Outcomes and Measures: The primary outcome was the state-month rate of unique individuals receiving 1 or more buprenorphine prescriptions for opioid use disorder per 100 000 residents (all-payer). Secondary outcomes were payer-specific rates-Medicaid, commercial, Medicare, and self-pay-each per 100 000 persons in the corresponding insured population. Results: As the first year of any expansion is 2014, 2013 served as the baseline year. In 2013, there were 659 046 unique patients, 58.2% were male, and the mean (SD) age was 36.6 (0.02) years. For 149 648 295 dispensations for 4 596 264 unique patients across 41 expansion states (including DC) and 10 nonexpansion states from 2013 to 2024, Medicaid expansion increased total buprenorphine treatment rates only in states expanding in 2019 or later (21.1% relative increase; average treatment effect on the treated, 28.67 per 100 000; 95% CI, 8.20-49.15 per 100 000). Gains were most pronounced in high-need recent expanders, such as Maine (57.22 per 100 000; 95% CI, 44.20-70.24 per 100 000), Virginia (44.46 per 100 000; 95% CI, 31.44-57.49 per 100 000), and Oklahoma (22.98 per 100 000; 95% CI, 12.84-33.12 per 100 000). Conclusions and Relevance: In this cross-sectional study using contemporary data and methods, post-2018 Medicaid expansions were associated with substantial increases in buprenorphine treatment, particularly in high-need states operating under newer prescribing regulations. These findings underscore Medicaid expansion's role in improving opioid use disorder treatment access and can inform state and federal efforts to expand evidence-based care.