Importance The Inflation Reduction Act (IRA) introduced significant reforms to Medicare Part D in 2025, aiming to reduce medication costs for beneficiaries by eliminating the coverage gap (“donut hole”) with a $2,000 annual out-of-pocket cap. However, insurers’ responses to these policy reforms—and their potential implications for medication affordability and access—have not been systematically evaluated.

Objective To assess how Medicare Part D plans adjusted benefit design and formulary structures in response to the IRA and determine the impact of these adjustments on beneficiaries’ financial responsibilities.

Design, Setting, and Participants Retrospective comparative analysis of Medicare Part D plans (Standalone Prescription Drug Plans [PDPs] and Medicare Advantage Prescription Drug [MAPD] plans), comparing plan structure, formulary coverage, utilization management, and cost-sharing details from January 2024 to January 2025. Analyses were conducted using publicly available Centers for Medicare & Medicaid Services (CMS) datasets.

Main Outcome(s) and Measure(s) Primary outcomes included changes in annual deductible amounts, cost-sharing structures (co-payment vs co-insurance), formulary coverage and utilization management practices, and patient out-of-pocket costs for GLP-1 medications, including first-fill cost burden.

Results Across PDPs, mean annual deductibles significantly increased from $384.7 (95% CI, 369.2–400.1) to $454.0 (95% CI, 432.9–475.1); MAPD plans showed a greater increase from $98.7 (95% CI, 93.6–103.8) to $249.0 (95% CI, 241.4–256.6). In MAPD plans, co-insurance style coverage utilization drastically increased for tier 3 medications (2024: 6.3%, 2025: 38.1%). Specifically, for GLP-1s, while overall coverage decreased, preferred drugs like Ozempic and Mounjaro experienced expanded coverage. However, first-fill out-of-pocket expenses increased substantially due to higher deductibles and increased costs associated with co-insurance style coverage. First-fill costs exceeding $600 rose from 40%-45% (2024) to over 80% (2025) in PDPs and from less than 1% to approximately 13% in MAPD plans.

Conclusions and Relevance Medicare Part D plans in 2025 were strategically designed to increase beneficiaries’ financial responsibilities via higher deductibles, increased co-insurance cost-sharing, and restricted formulary coverage. While overall annual patient medication cost burdens will decrease, the cost of filling each medication will increase, which may negatively impact medication access and adherence.

Question How did 2025 Medicare Part D plans respond and adapt to new IRA policies, and how is this affecting medication affordability and access?

Findings Part D plans have adopted higher deductibles, shifted from co-payment to co-insurance, and limited formulary coverage, which has increased beneficiaries’ financial responsibility and negatively impacted medication access.

Meaning Although IRA provisions may reduce patients’ annual medication out-of-pocket costs, Part D plans are adopting new strategies that increase patients’ financial challenges.

Dr. Yi Wolf Zhang and Dr. Michael G. Blyumin hold equity from MedHug.

This study did not receive any funding

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All data produced in the present study are available upon reasonable request to the authors