Geographic Availability and Use of Medications for Opioid Use Disorder Among Medicaid Enrollees.

Importance: There are large racial and ethnic differences in the use of medications for opioid use disorder (MOUD). Whether differences in geographic availability of MOUD providers (defined in this study as buprenorphine prescribers, methadone dispensing opioid treatment programs, and naltrexone prescribers) contribute to these differences in Medicaid is unknown. Objective: To examine differential geographic availability of MOUD in Medicaid and whether it is associated with MOUD use. Design, Setting, and Participants: This cross-sectional study analyzed the geographic availability of Medicaid prescribers of MOUD in 2021, spanning 10 states (Delaware, Kentucky, Maryland, Maine, Michigan, North Carolina, Pennsylvania, Tennessee, Virginia, and West Virginia) in the Medicaid Outcomes Distributed Research Network. The study population included Medicaid enrollees aged 18 to 64 not enrolled in Medicare and their MOUD providers. The data analysis was conducted from December 2022 to April 2026. Exposures: Geographic availability was measured at the zip code level (number of MOUD providers available in Medicaid within a 15-minute drive time per 100 Medicaid enrollees). Main Outcomes and Measures: Main outcomes included the probability of buprenorphine, methadone, and naltrexone use as a function of enrollee race and ethnicity, whether they had above-median geographic availability, and interactions between above-median geographic availability and race and ethnicity. Results: The sample included 8 081 899 Medicaid enrollees; 472 409 (5.8%) had an OUD diagnosis. The population was 58.7% female and 41.3% male. Among the study population, 11.7% were aged 18 to 20 years, 39.5% were aged 21 to 34 years, 21.4% were aged 35 to 44 years, 14.5% were aged 45 to 54 years, and 12.9% were aged 55 to 64 years. Overall, 7.3% of the sample were Hispanic enrollees, 27.4% were non-Hispanic Black enrollees, 56.2% were non-Hispanic White enrollees, and 7.2% were enrollees from other racial and ethnic groups. Overall, 13 575 buprenorphine prescribers, 516 methadone dispensers, and 4801 naltrexone prescribers billed Medicaid. Median Medicaid MOUD providers available within a 15-minute drive were 0.89 per 100 enrollees for buprenorphine, 0.03 for methadone, and 0.32 for naltrexone. Above-median geographic availability of methadone was associated with a 0.99 (95% CI, 0.54-1.42)-percentage point increase in methadone use for non-Hispanic White enrollees; there was no such increase for non-Hispanic Black or Hispanic enrollees. Evidence of similar differences was limited for naltrexone. Above-median availability of buprenorphine was not associated with increased use of MOUD for any racial or ethnic group. Conclusions and Relevance: In this cross-sectional study of 10 state Medicaid programs, greater geographic availability of MOUD was associated with increased use only for methadone and, to a lesser extent, naltrexone. No racial and ethnic groups experienced gains in use associated with improved access. Additional strategies beyond addressing geographic access may be needed to close racial and ethnic gaps in MOUD.