In the United States, pharmacy benefit managers (PBMs) provide patient access to medications through rebates and formulary management. PBMs employ various cost-containment measures, including tiered cost-sharing for different medication tiers, prior authorizations, and even doors with exclusions, among many others, all of which PBMs claim reduce spending on medications. While these policies aim to promote cost-effective prescribing and encourage the use of less expensive alternatives, such policies are often viewed unfavourably by physicians, who believe such restrictions can undermine clinical autonomy and delay access to care.
Recent Medicare Part D data indicate that the manufacturer rebates increased by an estimated $27 billion between 2016 and 2021, largely driven by formulary exclusions. These exclusions, along with the rationing of key medications for chronic conditions such as multiple sclerosis, raise questions about the impact of insurance policies’ design on patient outcomes and long-term health.
This retrospective analysis examined Medicare coverage from 2018 to 2022, focusing on enrollment, plan characteristics, and claims data. Patients were relapsing-remitting multiple sclerosis patients on disease-modifying therapy (DMT) for at least five consecutive quarters. Relapse events were measured using claims, and events occurring multiple times within 30 days were considered a single relapse. Formulary coverage plans for MS treatments were categorized into median or tertile groups, and patterns of prior authorization and step therapy were also evaluated. Controls were provided by demographics, comorbidities, and subsidy status, among other factors. Statistical analyses were conducted using logistic and count regression models with adjustments for repeated measurements, with significant differences at P <0.05. All analyses were performed between August 2024 and January 2025 by SAS 9.4.
Data were analyzed on intake Medicare beneficiaries with relapsing-remitting MS, 50,162 in stand-alone drug plans (PDPs) and 34,708 in Medicare Advantage drug plans (MA-PDs) across multiple beneficiary-quarter observations. The mean age was 58 years, and the majority of the participants were female. In PDPs, older, less subsidized, and more frequently White enrollees tended to be in high-coverage plans. In MA-PD patients covered by a high-coverage plan, members were also more likely to be White and reside in the Northeast or the West regions. PDPs covered 4 of 15 MS drugs (26.7%) and 4 of 7 classes (57.1%), compared to 8 drugs (53.3%) and five classes (71.4%) with MA-PDs. High formulary coverage was associated with lower relapse rates: PDPs (9.5% vs 10.6%) and MA-PDs (6.9% vs 7.8%) had adjusted ORs of 0.93 and 0.88, respectively.
This study shows that restrictive formularies under Medicare Part D are associated with increased relapse rates in patients with MS. Greater access to DMTs was linked to lower relapse risk, with a 12% reduction in the use of Medicare Advantage plans (other than drugs) and a 9% reduction in stand-alone drug plans. As there are more available options for the treatment of MS, there is a growing trend to limit options by insurance plans, which could negatively affect patient outcomes.
Study limitations include reliance on claims data, which may contain inaccuracies and cannot measure early-stage MS diagnosis, particularly in individuals under 65 years. Most relapses were identified through outpatient claims, and this might have underestimated serious attacks. Additionally, unmeasured factors related to the selection of patient plans, or a delayed effect of formulary changes, could not be fully accounted for.
In summary, although cost containment remains an important objective, overly restrictive formularies can harm MS patients by limiting access to individualized treatment options. Policymakers and payers should balance cost control with the need to preserve therapeutic diversity for complex chronic diseases such as MS.
References: Blaylock B, Van Nuys K, Joyce G. Formulary restrictions and relapse episodes in persons with relapsing-remitting multiple sclerosis. JAMA Netw Open. 2025;8(8):e2525155. doi:10.1001/jamanetworkopen.2025.25155
