The Changing Part D Landscape

Introduction Differences in how Medicare Advantage Prescription Drug plans (MA-PDs) and stand-alone Prescription Drug Plans (PDPs) are financed may contribute to fewer coverage options for traditional Medicare beneficiaries. The Inflation Reduction Act (IRA) capped annual out-of-pocket spending and reduced government reinsurance, thereby placing more cost responsibility on plans and manufacturers and potentially further limiting coverage. Methods This study draws on 2020–2025 data from the CMS Public Use Files to compare coverage options by cost-sharing categories (defined by mean premium and deductible) across plan types and plan sponsors. Results A majority of MA-PDs maintained low-premium and low-deductible designs (2020=66.0%, 2025=62.4%), reflecting cross-subsidies from integrated medical benefits, while enhanced PDPs increasingly pursued low-premium and high-deductible structures (38.2%, 51.5%) and basic/actuarially equivalent (AE) PDPs maintained high-premium and high-deductible structures (66.0%, 65.1%). In 2025, more than half of brand-only drugs in unprotected classes were excluded from Part D formularies (enhanced MA-PDs=51.8%, enhanced PDPs=57.3%, basic/AE PDPs=60.0%), especially in high-spending therapeutic areas. Conclusions Results reflect increasing consolidation and reduced plan diversity, with potential consequences for access and affordability among traditional Medicare beneficiaries. Policymakers may need to reconsider subsidy and risk-adjustment mechanisms to preserve competition and equitable access across plan types in the evolving Part D marketplace.