Trends in Medicare Part D Formulary Coverage for Non-insulin Diabetes Medications, 2020-2024

Diabetes is a chronic condition that affects over one-quarter of Medicare beneficiaries. It is treated with insulin and/or non-insulin medications, such as biguanides (e.g., metformin), DPP-4 inhibitors (e.g., sitagliptin), or GLP-1 s (e.g., semaglutide). Many diabetes medications are expensive and drive high treatment costs. Several recent clinical and policy changes may affect formulary design for drug classes used to treat diabetes in Medicare Part D, including changes to clinical guidelines to increase the emphasis on weight loss and the Inflation Reduction Act (IRA), which changed the Part D benefit structure, among other provisions. Given these policy changes, we assessed non-insulin diabetes drug coverage in Part D from 2020 to 2024 to establish baseline trends prior to the implementation of major IRA-related changes in 2025. We were particularly interested in examining coverage trends between Medicare Advantage Prescription Drug plans (MAPDs) and stand-alone prescription drug plans (PDPs), given the recent growth in the MAPD market. We excluded insulins due to the variety of policies affecting insulin coverage that did not affect other diabetes classes, such as recent manufacturer-led price decreases or the IRA's $35 insulin copay cap.