BACKGROUND: More than 30% of Medicare beneficiaries and 40% of patients dually eligible for Medicare and Medicaid use opioids. With an estimated 8%-12% of patients developing an opioid use disorder (OUD) after initiating opioids, opioid misuse is a significant public health challenge, especially among high-risk Medicare populations. Medication-assisted treatment (MAT) is the use of medications for the treatment of OUD and to prevent relapse to opioid use. MAT is the most effective treatment for OUD. There are a variety of barriers to MAT therapy that may delay access to treatment. OBJECTIVE:To study the impact of the removal of prior authorization requirements for MAT medications on MAT utilization, opioid utilization, and clinical outcomes, including emergency department visits, inpatient admission, relapse rates, behavioral health services, and nonopioid pain medication utilization, among opioid-using individuals with Medicare Advantage Prescription Drug (MAPD) coverage. METHODS:This retrospective, cross-sectional study used administrative medical, pharmacy, and enrollment data to identify chronic opioid users and a subset cohort initiating MAT use in 2017, when prior authorization requirements were in effect, and 2018 after removal of prior authorization requirements. Opioid and MAT utilization and clinical outcomes from emergency department visits were also examined before and after prior authorization requirements. A logistic regression analysis was conducted to examine the impact of the policy change on relapse rates, comparing relapse rates in 2017 and 2018, after controlling for potentially confounding demographic and clinical factors.