Buprenorphine is among the most effective drugs for treating opioid use disorder, yet only a quarter of Americans who need it receive it. Requiring prior authorization has been identified as an important barrier to buprenorphine access. However, the practice remains widespread in Medicaid-the largest insurer of Americans with opioid use disorder. In this study, we examined how prior authorization for buprenorphine is related to plan structure and state political environment, using data on all 266 comprehensive Medicaid managed care plans active in 2018. We found substantial variation in prior authorization use across states, with all plans requiring prior authorization in eleven states and no plans requiring it in thirteen other states. We found that for-profit plans and those located in Republican states were more likely to impose prior authorization policies. Our findings suggest that managed care plans' decisions regarding use of prior authorization may be shaped by internal pressures to control costs, as well as by differing partisan stances regarding the need to prevent criminal diversion of buprenorphine.