County-Level Context and Differential Policy Impacts on Buprenorphine Use Among Medicaid Enrollees with Opioid Use Disorder in Kentucky, 2018–2025

ABSTRACT PURPOSE To estimate changes in buprenorphine use among Kentucky Medicaid enrollees with opioid use disorder (OUD) after policy changes and pandemic disruptions, and whether impacts differed by county-level context, primarily rurality and, secondarily, opioid treatment program (OTP) availability. METHODS We analyzed Kentucky Medicaid claims from January 2018 through June 2025, identifying enrollees with diagnosed OUD to construct 10,800 county-month observations. Logistic regression fitted with weighted generalized estimating equations was used for statistical modeling of an interrupted time series (ITS) design to assess changes in the monthly proportion of enrollees with OUD receiving buprenorphine. Interruptions included removal of prior authorization (PA) requirements for transmucosal buprenorphine, methadone coverage initiation, COVID-19–related policy changes, and federal X-waiver elimination. Rurality and OTP availability were evaluated as effect modifiers. RESULTS The proportion of enrollees with OUD receiving buprenorphine increased from 0.29 to 0.45 across the study period. PA removal was associated with an immediate increase in the odds of buprenorphine use (odds ratio [OR]=1.043; 95% confidence interval [CI]=1.025, 1.061), corresponding to a 1.4-percentage-point increase. X-waiver elimination was associated with a sustained increase in trend (OR 1.007; 95% CI 1.004–1.010). Differential effects by rurality were limited to the COVID-19 period. Counties without an OTP responded more strongly to PA removal than counties with an OTP (P=0.037). CONCLUSIONS Removal of administrative and regulatory barriers was associated with increased buprenorphine use among Kentucky Medicaid enrollees with OUD, with effects varying by county-level context, particularly OTP availability.