Formulary-Related Insurance Denials of Single-Source Branded Drugs in the United States

Importance: Formulary exclusions and drug utilization management, including prior authorization and step therapy, reduce drug spending but may limit timely treatment access. Objective: To estimate formulary-based rejections and subsequent dispensing of initial attempts to fill single-source branded drug prescriptions. Design, Setting, and Population: Retrospective, national, all-payer cohort study using IQVIA Formulary Impact Analyzer, which represents anonymized, patient-level, adjudicated US outpatient pharmacy claims, from January 2018 through September 2024. The study focused on 1.17 million individuals attempting to fill 2 million single-source branded drug prescriptions for the first time. Exposure: Attempt to fill a single-source branded drug prescription for the first time. Main Outcomes and Measures: The primary outcomes were (1) rejection for formulary exclusion or utilization management (prior authorization or step therapy) of an initial prescription fill attempt and (2) failure of dispensing of the rejected molecule or another member of the same therapeutic class within 90 days of the initially attempted fill. Results: Among more than 2 million initial fill attempts (commercial insurance, 0.84 million; stand-alone Medicare prescription drug plan, 0.40 million; Medicare Advantage prescription drug plan, 0.39 million; Medicaid fee-for-service, 0.21 million; Medicaid managed care, 0.10 million; health insurance marketplace [exchange] plan, 0.06 million), 68.0% were paid on the initial fill attempt, while the remainder were rejected for formulary exclusion (14.8%) or rejected due to requiring prior authorization or step therapy, ie, utilization management (17.2%). Formulary-based rejections increased 67.4% over the time frame examined, from 24.3% (2018) to 40.7% (2024), and rejections were most common among exchange (48.7%) and Medicaid managed care (49.8%) compared with Medicare prescription drug plans (24.0%) and Medicare Advantage prescription drug plans (19.8%). Of the 32% of attempts that were initially rejected, 38.6% ultimately resulted in the rejected molecule being filled within 90 days and nearly half (48.4%) resulted in no medication fill in the same therapeutic class within that time frame. Treatment initiation was delayed an average of 12.2 days (SD, 17.8 days) after initial rejection among those ultimately receiving the same molecule or a therapeutic substitute. Conclusions and Relevance: Among this large, diverse sample of individuals in the United States, formulary rejections were frequent and often resulted in delayed or absent treatment, highlighting trade-offs between cost and access to medicines.