Uncovering the full economic impact of biosimilars: a “would have spent” counterfactual analysis of five reference biologics (infliximab, adalimumab, bevacizumab, rituximab, and trastuzumab) in the United States and Europe, 2016–2025

BACKGROUND: Originator biologic medicines have transformed care across immunology and oncology, but their cost burdens health systems. Biosimilars were introduced to stimulate competition and reduce spending. Conventional budget-impact models estimate savings as the price differential multiplied by biosimilar uptake, systematically underestimating impact by ignoring originator price reductions. OBJECTIVE: We apply a "would have spent" counterfactual framework across five high-cost reference biologics to capture the full economic value of biosimilars, including both direct savings from biosimilar uptake and indirect savings from competitive originator price concessions. METHODS: We analyzed the infliximab, adalimumab, bevacizumab, rituximab, and trastuzumab markets across the United States and Europe from 2016 to 2025 using IQVIA MIDAS sales and volume data. Observed spending was compared with a counterfactual assuming no biosimilar entry, with each originator held at its pre-competition peak price and savings counted only from the year of biosimilar entry. Savings were disaggregated by molecule and region, and translated into treatment capacity using indication-weighted annual doses. RESULTS: Across the five molecules, observed spending over 2016-2025 was $462.0B versus $558.5B projected under the no-biosimilar counterfactual, yielding $96.5B in cumulative savings (a 17.3% reduction). Savings were $30.4B (adalimumab), $29.3B (infliximab), $14.1B (bevacizumab), $12.4B (rituximab), and $10.1B (trastuzumab). On a constant-budget basis, the price reductions observed by 2025 could fund approximately 1.1 million additional patient-treatment years. Patterns diverged sharply by market: for adalimumab, savings were concentrated in Europe ($21.4B) rather than the United States ($9.0B), reflecting delayed U.S. biosimilar entry in 2023. CONCLUSIONS: The "would have spent" analysis reveals substantially greater benefits from biosimilars than conventional models suggest. By incorporating originator price response and accounting for the timing of competition, the approach captures "hidden" savings, (i.e. the additional reductions from originator price erosion that conventional price-differential models overlook) and exposes how market structure and entry timing shape value, reinforcing the case for policies that accelerate and sustain biosimilar competition.