PBM-affiliated private label biosimilars would seem to have a built-in formulary advantage. But for ustekinumab, that advantage has not carried over to Medicare Part D.
A recent JAMA Network Open study identified 12 ustekinumab products available for formulary coverage in early 2026. Yet the average Part D plan covered only 2.3 biosimilars. Even more surprising, PBM affiliated private label products were largely missing from formularies connected to their corporate siblings.
CVS Health’s Cordavis labeled Pyzchiva received no Part D coverage. Optum Rx’s Nuvaila labeled Wezlana appeared in just 0.4% of UnitedHealth plans.
The results run against the conventional logic of vertical integration. If a PBM can influence formulary placement, why not direct volume toward its own product like in commercial formularies? The answer lies in the Inflation Reduction Act’s (IRA) Part D redesign, which made the economics of an affiliated private label biosimilar potentially less attractive in Medicare than in the commercial market.
Below, we follow the incentives that help explain why PBM-affiliated biosimilars remain largely absent from Medicare Part D formularies.
PBMs still pick the pharmacy benefit winners
The study does not show that PBMs have lost their role as the gatekeepers of the pharmacy benefit biosimilar market. The three largest PBMs manage roughly 80% of prescription drug volume, and each operates an affiliated private label drug business. See The Top Pharmacy Benefit Managers of 2025: Market Share and Key Industry Developments. Note that Cigna no longer participates in Part D as a plan sponsor. It sold its Medicare Part D business to HCSC in March 2025, and those plans now operate under the HealthSpring brand.
PBMs still hold the levers that determine market share, including preferred formulary placement, utilization management, and specialty pharmacy access. What has changed is the economics behind those decisions. The IRA widened the financial differences between commercial insurance and Medicare Part D, resulting in different formulary strategies across the two markets.
The commercial playbook still works
Affiliated biosimilars can keep product economics inside the parent corporation in both commercial insurance and Medicare Part D. The advantage is greater in commercial coverage, where the manufacturer affiliate does not incur the statutory Part D discount obligation. That helps explain why PBM-affiliated products have played such a visible role in commercial formularies. In Part D, the retained product economics must offset both the plan’s share of the claim and the affiliated manufacturer’s statutory liability.
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The confidential math includes dead net acquisition costs, rebates, fees, affiliate margins, and internal transfer pricing. Formulary share can create gross value for the parent corporation, but the net value depends on whether the retained economics exceed the additional liabilities created by the product.
That model may face more limitations beginning in 2028. Federal reforms taking effect that year will require Part D PBMs to remit rebates and other remuneration to plan sponsors, disclose detailed pricing information, and delink their compensation from drug prices and utilization. Proposed FTC consent orders involving Express Scripts and CVS Caremark would also restrict preference for higher-list-price versions of the same drug in their standard formulary offerings. See The FTC Blows Up Express Scripts’ PBM Model. These changes would materially realign channel incentives around net price, advancing what we call the Net Pricing Drug Channel #NPDC. Check out this video clip from our 2026 Webinar Series where Adam Fein explains how net prices are reshaping access, economics, and competitive strategy.
The IRA made both the plan and manufacturer write bigger checks
The Part D redesign changed the calculation for both the plan and manufacturer sides of a vertically integrated company. The shift is easiest to see in the catastrophic phase.
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Plan exposure in the catastrophic phase jumped from 20% to 60%, while manufacturers took on a new 20% catastrophic obligation under the Manufacturer Discount Program, along with a 10% obligation in the initial phase. A vertically integrated company offering a private label biosimilar can therefore write two bigger checks: one through its Part D plan and another through its manufacturer affiliate. In the catastrophic phase, those obligations add up to 80% of the drug’s cost. That is where the disincentives start to build.
For an independent biosimilar, the manufacturer funds its statutory discount outside the PBM organization. For a PBM-affiliated private label biosimilar, the plan liability and manufacturer obligation can both land inside the same corporation.
Follow the Part D money
The chart below applies the 2026 defined standard Part D benefit to the study’s gross prices. It assumes six fills of a 90 mg syringe, no other prescriptions, no rebates, a $615 deductible, and a $2,100 out of pocket cap.
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The conclusion is straightforward. In Part D, the lower-priced traditional biosimilar reduces plan exposure, while the unaffiliated manufacturer bears the statutory discount. Pyzchiva illustrates the difference: The $4,390 manufacturer obligation falls on Sandoz under its label but becomes part of CVS’ economics under the Cordavis private label. Cordavis Pyzchiva’s absence from Part D suggests those economics may not offset the added obligation.
The channel matters
The JAMA results therefore are less mysterious than they appear. PBMs still control which pharmacy benefit biosimilars win, they just don’t always want it to be their own.
Commercially, an affiliated product can preserve value within the organization. In Part D, the IRA exposes the plan to more of the claim while imposing a statutory obligation on the manufacturer affiliate. A lower priced independent biosimilar shifts that obligation to another entity: the manufacturer.
Patients using these products are likely to reach the 2026 $2,100 cap, so the immediate OOP difference for the patient at the pharmacy counter is limited.
Higher plan liability can flow through to future premiums and taxpayer-funded subsidies, while manufacturers separately absorb their statutory discount obligations.
The math helps explain why private label ustekinumab products have largely stayed out of Medicare formularies. PBMs can favor their own products on formulary, but Part D makes that choice more expensive for the parent company.
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