This study investigates whether the introduction of biosimilars has led to lower out-of-pocket (OOP) costs for patients using biologic drugs in the US. Using a national commercial claims database, the researchers analyzed claims from 190,364 individuals who used one of seven clinician-administered biologics between 2009 and 2022. The primary outcome was OOP spending on biologics, including deductibles, copayments, and coinsurance. The study found that annual OOP costs increased or remained stable for most biologics even after biosimilar competition began. In the second year after biosimilar competition started, the adjusted odds ratio of nonzero annual OOP spending was 1.08 (95% CI, 1.04-1.12), and the average nonzero annual spending was 12% higher compared to the year before biosimilar competition. Claims for biosimilars were more likely to have nonzero OOP costs than reference biologics, but the mean nonzero OOP costs were 8% lower for biosimilars. However, these findings varied by drug, with some newer biosimilars showing lower OOP costs. The study concludes that biosimilar competition has not consistently reduced patient OOP costs, highlighting the need for targeted policy interventions to ensure that savings from biosimilar competition improve affordability and access to biologics.This study investigates whether the introduction of biosimilars has led to lower out-of-pocket (OOP) costs for patients using biologic drugs in the US. Using a national commercial claims database, the researchers analyzed claims from 190,364 individuals who used one of seven clinician-administered biologics between 2009 and 2022. The primary outcome was OOP spending on biologics, including deductibles, copayments, and coinsurance. The study found that annual OOP costs increased or remained stable for most biologics even after biosimilar competition began. In the second year after biosimilar competition started, the adjusted odds ratio of nonzero annual OOP spending was 1.08 (95% CI, 1.04-1.12), and the average nonzero annual spending was 12% higher compared to the year before biosimilar competition. Claims for biosimilars were more likely to have nonzero OOP costs than reference biologics, but the mean nonzero OOP costs were 8% lower for biosimilars. However, these findings varied by drug, with some newer biosimilars showing lower OOP costs. The study concludes that biosimilar competition has not consistently reduced patient OOP costs, highlighting the need for targeted policy interventions to ensure that savings from biosimilar competition improve affordability and access to biologics.