Biosimilar adoption in the United States is accelerating. By the end of 2025, the US biosimilar market reached a significant milestone of 90 total approvals, with 63 having successfully reached the commercial market. Utilization is growing, according to PSG’s 2025 Artemetrx State of Specialty Spend and Trend Report. Overall biosimilar utilization increased from 27.3% in 2023 to 36.7% in 2024. The directive across health plans, TPAs, and the employer groups they serve is increasingly clear: transition where you can, manage the cost, capture the savings. PubMed Central
That directive is sound. The savings are real. IQVIA has documented $56 billion in biosimilar-related savings between 2013 and 2022.
What’s less examined is whether biosimilar transition decisions, particularly those affecting physician-administered specialty drugs under the medical benefit, are being made with a complete financial picture. Specifically, whether the manufacturer’s rebate picture on both sides of the transition has been mapped before the switch is made.
Two Channels, Two Different Dynamics
Most biosimilar strategies in the market have been built around the pharmacy benefit. That makes sense, the pharmacy benefit is where PBM contract structures, formulary placement, and rebate guarantees are most visible and most contested.
The rebate dynamics on the pharmacy side are well-documented. As research from Duke University’s Health Policy Institute and IQVIA has shown, reference biologic manufacturers have historically defended formulary position through substantial rebate programs, creating barriers to biosimilar adoption even when the biosimilar carried a lower list price. IQVIA found it took four to five years for infliximab biosimilars to achieve meaningful formulary uptake, despite lower prices, largely due to these commercial dynamics.
The medical benefit operates differently. Physician-administered specialty drugs — infused biologics, oncology agents, and related high-cost therapies- are billed as medical claims, reimbursed through ASP-based pricing under Medicare Part B, and managed through a separate set of manufacturer rebate programs that exist independently of any PBM contract. The rebate wall dynamics that define pharmacy benefit biosimilar strategy simply don’t apply in the same way here.
What does apply is a different and less frequently asked question: when an organization transitions from a reference biologic to a biosimilar on the medical benefit, has anyone mapped what manufacturer rebate programs existed on the reference product, and what programs, if any, apply to the biosimilar?
The Data Points to a Gap
PSG’s 2026 Trends in Specialty Drug Benefits Report surveyed 228 benefits leaders and found that only 18% of employers are applying biosimilar strategies to both pharmacy and medical benefits, compared to 56% of health plans. The majority of organizations with active biosimilar programs have built them on the pharmacy side. The medical benefit is largely operating outside that framework.
That gap matters for the rebate question in two distinct ways.
For organizations that were capturing manufacturer rebates on a reference biologic under the medical benefit, a process that, as PSG’s data shows, only about half of organizations have in place at all, a biosimilar transition changes the rebate picture. The reference biologic rebate program no longer applies. Whether the biosimilar carries an equivalent program, a different program, or no program at all is a question that needs an answer before the transition is finalized, not after.
For organizations that weren’t capturing medical benefit rebates on the reference biologic, the transition doesn’t change that situation. But it also doesn’t improve it. The medical benefit rebate channel remains unaddressed regardless of which drug is being administered.
In either case, the financial analysis is incomplete without the medical benefit rebate layer.
What This Means by Audience
For health plans managing Part B and Part C populations, biosimilar transitions in oncology, rheumatology, and infusion categories affect medical benefit drug mix in ways that have direct rebate implications. Health plans are better positioned than employers on cross-benefit biosimilar strategy, 56% are applying the strategy to both benefits, but that still leaves a significant share without a complete framework. For health plans with active formulary optimization programs, the rebate map on both sides of a biosimilar transition is a reasonable addition to the standard analysis.
For TPAs and self-funded employers, the gap is more significant. With only 18% applying a biosimilar strategy to both benefits, most employer groups are making biosimilar decisions almost entirely through the pharmacy channel. For employers with meaningful exposure to medical benefit specialty spend, infusion therapy, administered oncology agents, and high-cost biologics, the medical benefit layer of the biosimilar savings calculation is largely invisible. TPAs advising these groups are well-positioned to surface the question if they know how to ask it.
What to Watch
1. The biosimilar pipeline affecting the medical benefit is expanding. Oncology biologics, including bevacizumab, trastuzumab, and rituximab, all primarily administered under the medical benefit, have established biosimilar competition with utilization ranging from high to dominant in some categories. New entrants across immunology and infusion categories continue. The question of what manufacturer rebate programs apply to each product in this evolving mix is a moving target that warrants periodic review.
2. Cross-benefit optimization is becoming a standard expectation. PSG’s 2026 survey found that two in three payers are focusing on cross-benefit specialty formulary optimization. As that becomes standard practice, a biosimilar strategy that only addresses the pharmacy channel will increasingly look like an incomplete program, not just to internal stakeholders, but to plan sponsors and employer clients asking harder questions about specialty cost management.
3. Rebate programs on biosimilars are not uniform. Manufacturer rebate programs on biosimilars vary significantly by product, by channel, and by contract structure. Unlike the pharmacy benefit, where PBM formulary rebate structures are broadly understood, medical benefit rebate programs require direct engagement to understand what’s available. That engagement doesn’t happen automatically when a biosimilar transition is made.
4. The medical benefit rebate gap documented in PSG’s data applies to biosimilars, too. Only 51% of organizations receive medical benefit rebates at all, per PSG’s 2026 survey. For organizations making biosimilar transitions on the medical benefit without a rebate management process already in place, the transition doesn’t close that gap — it just changes which drug is running through it.
The Practical Starting Point
The biosimilar savings case is directionally sound and broadly supported by the data. The question worth asking before the next transition decision is whether the analysis covers both channels, specifically, whether the rebate picture on the medical benefit has been mapped for the drug being replaced and the drug being adopted.
For most organizations, that question hasn’t been formally asked. Asking is a reasonable starting point before assuming the savings projection is complete.
As biosimilar adoption continues to expand, is the medical benefit rebate picture part of your organization’s transition analysis, or is that layer still unaddressed? Share your perspective in the comments.
Disclaimer: This newsletter references publicly available findings from Pharmaceutical Strategies Group’s 2026 Trends in Specialty Drug Benefits Report and the 2025 Artemetrx State of Specialty Spend and Trend Report, as well as publicly available research from IQVIA, Duke University Health Policy Institute, and peer-reviewed publications. VativoRx is not affiliated with, endorsed by, or partnered with any source referenced. This newsletter is provided for informational and educational purposes only and does not constitute legal, regulatory, clinical, or financial advice. Readers should consult appropriate advisors regarding specific circumstances.
