Biosimilars: Is Your Self-Funded Plan Still Paying Brand Prices?

What biosimilars are, and why they matter now

A biosimilar is a biologic medicine the FDA has determined is highly similar to an existing "reference" biologic, with no clinically meaningful differences. Because biologics are among the most expensive drugs a plan covers, even a modest discount on one molecule can move total plan spend.

The regulatory path has also gotten simpler. In June 2024, FDA draft guidance said switching studies are generally no longer needed to show a biosimilar is interchangeable, the designation that lets pharmacists substitute it for the brand without a new prescription, subject to state law. source

A familiar renewal conversation

Here's a conversation that plays out at plenty of renewal meetings. The CFO asks whether the plan is "on the Humira biosimilars." The PBM account manager says yes, the biosimilar is on the formulary and adoption is high. Everyone moves on. A year later, someone finally pulls claims by product and finds the plan has been paying for a biosimilar version listed at nearly the same price as Humira, with the difference made up in rebates that arrive months later and don't fully cover it.

Nobody lied in that meeting. "On the biosimilar" and "paying a biosimilar price" just aren't the same question. The rest of this article is about asking the second one.

Where the market is now

Sources: PSG Biosimilars Review & Report.

Stelara (ustekinumab) followed Humira. Several ustekinumab biosimilars launched in 2025, including Wezlana, Selarsdi, Pyzchiva, and Steqeyma, and several were priced about 85% below Stelara's wholesale acquisition cost. source source More biologics are losing exclusivity over the next few years, so this is becoming a recurring opportunity, not a one-time event.

The catch: list price vs. what your plan pays

High biosimilar adoption across the market doesn't mean your plan is getting the savings. Three things get in the way:

1. Dual list prices. Some biosimilars are sold at two list prices: a "high" version near the brand's price, which supports rebates, and a "low" version priced far below it. If your PBM prefers the high-list version, your plan may see little change in net cost.
2. Brand still preferred. Some formularies kept the brand at a preferred tier, or cover brand and biosimilar equally, so prescribing doesn't move.
3. Medical benefit lag. For infused biologics billed through the medical plan, biosimilar adoption depends on provider buying decisions and how your medical plan reimburses, not your PBM formulary.

The fix is to measure net cost per claim by molecule. For each biologic with a biosimilar available, compare what the plan paid for the brand and each biosimilar version, after rebates and fees.

Private-label biosimilars

A newer development: several PBMs now distribute biosimilars under private labels through affiliated companies. Private labeling has helped drive rapid adoption, but researchers have flagged questions about competition and about who captures the savings along the supply chain. source

For a plan sponsor, the practical questions are what the plan pays per claim for the private-label product, whether that's lower than other available biosimilars, and what compensation the PBM's affiliates earn on it. Federal PBM reform will require more of this disclosure; see Federal PBM Reform and Employer Plans.

Switching members well

How a switch is handled affects whether it sticks. A study of more than 22,000 patients in a rheumatology registry found that new use of one adalimumab biosimilar jumped to about 24% the month after a major PBM formulary change, then fell by nearly 14 percentage points the following month. The lead researcher pointed to the "nocebo" effect, where patients expect a new product to work worse, as a likely factor. source

Plans that switch successfully usually:

• Communicate early with members and prescribers, explaining that biosimilars are FDA-approved and clinically equivalent.
• Offer a clear exception process for members with documented clinical reasons.
• Align member cost sharing so the biosimilar is the cheaper choice for the member, too.
• Check pharmacy network readiness, including specialty pharmacy supply of the preferred product.

Pharmacy benefit vs. medical benefit biosimilars

Biosimilars show up in two very different places, and each needs its own approach:

On the medical side, a provider paid as a percentage of a drug's price can earn more by giving the higher-priced product, which works against biosimilar adoption. Your medical carrier or TPA can help you see which products providers are billing and how they're reimbursed.

Questions to ask your PBM

1. For each biologic with a biosimilar, which product is preferred on our formulary, and is it the high-list or low-list version?
2. What did our plan pay per claim, net of rebates and fees, for the brand and each biosimilar last quarter?
3. Is the brand still covered, and at what tier and member cost share?
4. Do you or an affiliate own or distribute a private-label biosimilar, and what does your organization earn on it?
5. How are rebates on the brand affecting which product is preferred?
6. What's your plan for the next biosimilar launches, and how will our plan be moved?
7. What member and prescriber communication and exception process do you provide when you switch products?

What's next

Humira and Stelara were the first big waves, not the last. More high-cost biologics are scheduled to face biosimilar competition over the next several years, and FDA's simpler path to interchangeability should make substitution easier. source Plans that build a repeatable process now, reviewing net cost by molecule each quarter and acting when a new biosimilar launches, will capture each wave instead of waiting for their PBM to act.

Biosimilar checklist for self-funded plans

1. List every biologic your plan pays for that has an FDA-approved biosimilar.
2. Pull claims by molecule and product: brand vs. each biosimilar, on both pharmacy and medical benefits.
3. Compare net cost per claim after rebates and fees, not list price or rebate totals.
4. Ask which version is preferred (high- or low-list price) and why.
5. Check brand coverage and tiering, and whether member cost sharing favors the biosimilar.
6. Ask about private-label products and affiliate compensation.
7. Review medical-benefit biologics and how providers are reimbursed for biosimilars.
8. Plan member communication and an exception process before any switch.

Frequently asked questions