Differences in medicaid expansion effects on buprenorphine treatment utilization by county rurality and income: A pharmacy data claims analysis from 2009-2018.

Background: Although use of buprenorphine for treating opioid use disorder increased over the past decade, buprenorphine utilization remains limited in lower-income and rural areas. We examine how the Affordable Care Act Medicaid expansion influenced buprenorphine initiation rates by county income and evaluate how associations differ by county rural-urban status. Methods: This study used nationwide 2009-2018 IQVIA retail pharmacy data and a comparative interrupted time series framework-a hybrid framework combining regression discontinuity and difference-in-difference approaches. We used piecewise linear estimation to quantify changes in buprenorphine initiation rates before and after Medicaid expansion. Results: The sample included observations from 376,704 county-months. We identified 5,227,340 new buprenorphine treatment episodes, with an average of 9.2 new buprenorphine episodes per month per 100,000 county residents. Among urban counties, those with the lowest median incomes experienced significantly larger increases in buprenorphine initiation rates associated with Medicaid expansion than counties with higher median incomes (5-year rates difference est=3525.3, se=1695.3, Conclusions: Medicaid expansion was associated with a reduction in income-related buprenorphine disparities in urban counties, but not in rural counties. To achieve more equitable buprenorphine access, future policies should target low-income rural areas.