["Journal of Policy Analysis and Management, Volume 45, Issue 3, Summer 2026. ", "\nABSTRACT\nOlder adult opioid overdose deaths have increased over the past two decades in the United States. Methadone, one of three medications approved for opioid use disorder (OUD) treatment, was not covered by Medicare—the primary insurer of Americans 65 years and older—for OUD until 2020. We study the response of opioid treatment programs (OTPs), the only healthcare providers that can dispense methadone for the treatment of OUD in the United States, to this policy change using administrative data and a difference‐in‐differences framework. We find an increase in Medicare acceptance by OTPs and in the number of methadone treatment episodes post‐policy. Further, we document spillovers to other insurance markets and changes in (non‐methadone) treatment services offered by OTPs, suggesting that Medicare's entrance into this market has implications for all OUD patients receiving methadone treatment in OTPs.\n"]