S1981 Trends in Out-of-Pocket Spending for Drugs Under Medicare Part D in Moderate to Severe Inflammatory Bowel Disease and the Impact of the Inflation Reduction Act

Introduction: Treatments for moderate to severe inflammatory bowel disease (IBD) include biologics or small molecules. Most are branded with limited generic substitution, resulting in high out-of-pocket (OOP) expenses that can lead to premature drug discontinuation. We aimed to assess trends in OOP costs for key IBD therapies covered under Medicare Part D and evaluate the financial impact of the Inflation Reduction Act (IRA) $2,000 OOP cap implemented in 2025. Methods: We analyzed Medicare Part D Prescription Drug Plan Formulary and Pricing Files from Q3 (July–September) of 2019–2024 and Q1 of 2025. Eight available IBD drugs were included: adalimumab, tofacitinib, upadacitinib, ustekinumab, risankizumab, guselkumab, certolizumab and golimumab. Annual retail and OOP costs were estimated (maintenance doses for ustekinumab and risankizumab and both induction and maintenance doses for the rest) per drug using Medicare Part D benefit structures for each year. Costs were inflation-adjusted to 2025 U.S. dollars using a standardized conversion factor. Data analysis was performed in Stata 18; time trends were visualized using R. Results: Between 2019 and 2024, median annual OOP costs for most agents ranged from $4,000 to $13,000. In 2025, OOP costs dropped sharply to the $2,000 cap or below for all agents, while retail prices remained stable or slightly increased. Interrupted time series analysis demonstrated a significant policy-driven decline in OOP spending after 2025 across most drugs (excluding adalimumab and risankinumab due to insufficient data) with absolute reductions ranging from $3,283–$10,922 (P < 0.05). Conclusion: Implementation of the IRA's $2,000 OOP cap in 2025 was associated with a marked and immediate reduction in financial burden for high-cost IBD therapies. Our findings highlight the potential of policy interventions to improve medication affordability and support adherence for Medicare beneficiaries.