BACKGROUND: Assessing primary medication nonadherence, the rate at which a medication is prescribed for a patient but is not obtained or replaced with an alternative medication within a reasonable time period, can provide a better understanding of the frequency and impact of these barriers to medication access. Previous literature has reported high rates of primary medication nonadherence, ranging from approximately 20% to 55% in patients with rheumatoid arthritis (RA) treated with specialty disease-modifying antirheumatic drugs (DMARDs). The high primary medication nonadherence rate may reflect the difficulties associated with obtaining specialty medications, such as high costs, extended prior authorizations, and pretreatment safety requirements. OBJECTIVE: To evaluate reasons for and rates of primary medication nonadherence to specialty DMARDs in patients with RA referred to an integrated health systems specialty pharmacy. METHODS: We conducted a retrospective cohort study examining eligible patients with a specialty DMARD referral from a health system rheumatology provider to the health system specialty pharmacy. Initially, pharmacy claims were used to identify primary medication nonadherence, defined as the lack of a fill event within 60 days following the medication referral for patients without a specialty DMARD claim in the 180 days prior. Referrals from July 1, 2020, to July 1, 2021, were eligible. Exclusion criteria included duplicate referrals, use for non-RA indications, switches to clinic-administered therapies, and alternate filling methods. Medical record reviews were conducted to confirm referral outcomes. Outcomes included rate of and reasons for primary medication nonadherence. RESULTS: We included 480 eligible patients, 100 of whom had no documented fill event. After medical record review, 27 patients were removed due to having a non-RA diagnosis and 65 patients were removed due to having alternative fill methods, most due to external prescription routing (83.1%). The final primary medication nonadherence rate was 2.1%. Out of the 8 cases of true primary medication nonadherence, 3 patients held specialty DMARD therapy because of other existing disease states, 3 patients were unreachable, and 2 patients were unable to afford medication. CONCLUSIONS: Rates of primary medication nonadherence to specialty DMARDs were low in patients with RA managed by a health system specialty pharmacy. A total of 8 primary medication nonadherence cases were related to safety concerns in non-RA diseases states, patient unreachability, and affordability. However, the limited number of primary medication nonadherence cases limits the generalizability of reasons for primary medication nonadherence found in this study. Key elements of the health systems specialty pharmacy model that likely contribute to low primary medication nonadherence include dedicated financial assistance navigation services, in-clinic pharmacist availability, and open communication between provider offices.