This brief describes our approach to estimating the basic and inflationary federal rebates for medications to treat opioid use disorder and overdose (MOUDs) administered through the Medicaid Drug Rebate Program in state Medicaid programs. We developed this methodology, which relies only on publicly available data, as part of a larger project, Tracking Medicaid-Covered Prescriptions to Treat Opioid Use Disorder. We find that the estimated basic and inflationary federal rebates for MOUDs substantially reduced net Medicaid spending across all study years (2011–18). According to Medicaid State Drug Utilization Data, these rebates reduced net Medicaid spending by

• 34 percent for buprenorphine products (39 percent for brand-name and 6 percent for generic),
• 50 percent for naltrexone (54 percent for brand-name and 7 percent for generic), and
• 56 percent for naloxone (60 percent for brand-name and 21 percent for generic).

We find that accounting for federal rebates is possible using publicly available data, and may be important for analyses such as measuring the cost effectiveness of MOUDs. This methodology for estimating rebates can also be applied to other outpatient medications reimbursed by Medicaid.