Biosimilars in the U.S.: how adoption can change patient spending

Somewhere between a specialty pharmacy receipt and a late-night insurance portal login, I realized I’d been quietly building a mental spreadsheet about biologic drugs and how much they were shaping a family budget. Biosimilars had been a headline for years, but it finally clicked for me that adoption isn’t just a policy story—it’s a checkout-counter story, a premium story, a “can I start treatment this month” story. So I wrote down what I wish I had found in one place: what biosimilars are, why they don’t behave like generics, and how broader adoption can (and sometimes doesn’t) change what patients pay out of pocket—without promising miracles.

The moment the idea felt real

A friend texted me a photo: same active ingredient, two brand names, two very different prices. I went from “Huh?” to “Okay, but why?” in about six minutes. The short version is that biosimilars are highly similar to already approved biologics and have no clinically meaningful differences in safety or effectiveness. The FDA has a plain-language explainer that I found refreshingly direct (FDA biosimilars basics). There’s also a separate term, “interchangeable,” that matters mostly at the pharmacy counter because it can allow substitution per state law—the FDA’s overview makes this clearer than most (FDA 9 things to know).

Here’s the takeaway that finally stuck: adoption is about incentives as much as science. The clinical case is solid. The price you see (and the price you pay) is shaped by formularies, contracting, and benefit design. That’s where the spending story comes alive.

• Bookmark the FDA pages above to ground yourself in definitions before diving into costs.
• Know your benefit type: self-injected drugs are often billed under pharmacy benefits (Part D/commercial), while infusions often run through medical benefits (Part B/commercial medical).
• Expect variation: two patients can pay very different amounts for the same molecule depending on plan design, formulary tiering, and assistance programs.

Why biosimilars don’t act like small-molecule generics

When a generic pill arrives, prices typically freefall. Biologics are different: they’re large, complex molecules, and making a biosimilar requires expensive manufacturing and data packages. That keeps the number of competitors lower and the list-price discounts more modest than the 80–90% we see with generics. On top of that, pharmacy benefit managers and payers sort products into tiers and negotiate rebates. The FTC’s ongoing review of PBM practices outlines how these middle-layer incentives can affect what reaches patients at the counter (FTC PBM interim report).

I try to keep one mental model: patients feel prices through coinsurance, deductibles, and caps. If a plan’s negotiated price for a biosimilar is lower and your cost share is a percentage, then your out-of-pocket goes down. If a reference biologic has better rebates and preferred formulary placement, the biosimilar’s lower list price may not matter to you personally unless your plan actually adopts it as preferred.

Part D and the new out-of-pocket cap are changing the math

For people on Medicare drug plans, 2025 is a big turning point. There’s now a $2,000 annual cap on out-of-pocket prescription drug costs in Part D under the Inflation Reduction Act (CMS 2025 Part D fact sheet). That cap sets an upper bound on what patients pay, but it doesn’t erase the monthly reality of coinsurance and deductibles—especially early in the year. Here’s how I think about it:

• If your plan places a biosimilar on a lower tier or with lower coinsurance than the reference biologic, you may hit the cap later in the year, which spreads costs.
• If your plan prefers the reference biologic (because of rebates or contracts), your pharmacy counter price might not fall until the plan changes its formulary strategy.
• The cap makes catastrophic “tail” costs less scary, but adoption still matters for monthly affordability and for premiums over time.

Part B has a quiet but important incentive

Medical-benefit biologics (think clinic or infusion center) have their own adoption story. To nudge uptake, Medicare Part B temporarily increased the add-on payment for certain qualifying biosimilars to ASP + 8% of the reference product’s ASP (instead of +6%), for five years starting October 1, 2022. CMS spells this out in its biosimilar FAQs (CMS biosimilar FAQs). The idea is that clinics won’t be financially penalized for choosing the lower-priced product. Patients under Part B usually face coinsurance (often 20%, sometimes covered by supplemental insurance), so lower allowed amounts can translate into lower out-of-pocket bills—if the biosimilar is administered.

Where savings have already shown up

Zooming out helps. HHS’s Office of the Assistant Secretary for Planning and Evaluation analyzed Medicare Part B and reported that biosimilar competition reduced program spending and beneficiary out-of-pocket costs by about 62% on these drugs in 2023 (ASPE 2025 issue brief). That doesn’t mean every patient saw a 62% drop; it means that, at the program level, competitive pressure meaningfully lowered the amounts being paid. It’s the sort of macro signal that tells me adoption isn’t theoretical anymore.

On the pharmacy side, I’ve learned to check the plan’s drug spending dashboards and formulary notices each year. CMS’s public fact sheets and tools are a good reality check on how policy filters down to what a person might pay over months—not just over a calendar year cap (CMS 2025 cap again for quick reference).

What actually changes for a person at the counter

I keep a small checklist now, both for myself and to share with friends who ask “will a biosimilar help me?”

• Formulary status matters: Is the biosimilar preferred or non-preferred? Is there step therapy requiring the brand first?
• Your cost share type matters: Percent coinsurance amplifies price differences; flat copays may blunt them.
• Pharmacy-level substitution varies: For self-injected products, interchangeability plus state law can allow substitution; otherwise your prescriber may need to write the biosimilar by name (FDA on interchangeability).
• Site of care matters: Infusions billed under Part B or a medical benefit follow different rules and incentives than pharmacy claims under Part D.
• Time matters: Plans re-contract every year; a “no” in January can become a “yes” after a midyear update or at the next plan year.

PBMs and the invisible levers I didn’t see at first

When I traced why a lower list price didn’t equal a lower copay, the story often led to rebates and formulary placement. The FTC’s interim report describes how PBM contracting can privilege higher-rebate, higher-list-price options, even when a lower-price competitor exists (FTC PBM interim report). That’s not the whole market, and many plans do move to biosimilars—but it explains why adoption can feel lumpy and slow. The patient-facing translation: ask your plan for the “preferred” product and its negotiated price. Sometimes a biosimilar is preferred; sometimes the legacy brand is.

Simple ways I’m navigating choices without getting lost

I’m not trying to be my own pharmacist. I just try to ask the right questions in the right order.

• Step 1 Confirm the basics: diagnosis, intended molecule, and route (self-inject vs infusion). Then check the FDA page for a ground-truth definition if I’m confused (FDA biosimilars basics).
• Step 2 Compare what my plan prefers: call the plan or check the portal for tiering, coinsurance %, and any prior authorization/step therapy. Specifically ask whether a biosimilar is preferred.
• Step 3 Confirm dollars: ask the pharmacy for the claim-estimate on both the reference and the biosimilar. With Part B infusions, ask the clinic what your coinsurance would be if they administer a biosimilar.

Little habits I’ve been testing in real life

Some of this sounds mundane, but these were the small moves that changed my monthly bill more than I expected.

• Ask about switching pathways: If your prescriber wrote the reference product, ask whether a biosimilar is an option and what paperwork is needed. In some states, pharmacy substitution for an interchangeable works; in others, you’ll need a new script (FDA on state substitution).
• Time refills around deductibles: Early-year refills can be expensive when deductibles reset. If a biosimilar lowers the allowed amount under your plan, it can soften this spike even if you still hit the annual cap later (CMS Part D cap).
• Bring coverage letters to clinic visits: For infusions, I now show the benefit determination to the infusion nurse or financial counselor so they know my plan will cover the biosimilar under Part B’s reimbursement rules (CMS biosimilar FAQs).

Signals that tell me to slow down and double-check

I’m not a clinician, so I pause when any of these pop up:

• New or worsening symptoms after a switch—call the prescriber. Differences in device, injection volume, or schedule can matter even when the active molecule is highly similar.
• Surprise bills for an infusion or injection—ask whether the claim was billed as the biosimilar NDC/J-code and whether your plan recognizes it as preferred (CMS coding and payment in FAQs).
• Confusing pharmacy substitutions—remember that interchangeability governs pharmacy-level substitution, and state laws vary (FDA explainer).

What adoption means for program spending versus my wallet

A helpful mindset shift for me: program-level savings and personal affordability are related but not identical. ASPE’s analysis shows substantial reductions in Medicare Part B spending and beneficiary out-of-pocket on the affected drugs (ASPE 2025 issue brief). Meanwhile, the Part D $2,000 cap changes risk exposure for individuals in 2025 (CMS fact sheet). Over time, wider biosimilar adoption can also influence premiums if plan spending falls. But month to month, it still comes down to whether your plan actually prefers the biosimilar and what your cost-sharing formula is.

Quick official explainers I bookmarked

• FDA biosimilars basics
• FDA interchangeability overview
• CMS Medicare Part B biosimilar FAQs
• CMS 2025 Part D cap fact sheet
• ASPE 2025 Part B analysis

What I’m keeping and what I’m letting go

I’m keeping a few principles on a sticky note: 1) Start with the FDA definition so I don’t get spooked by branding differences; 2) find out what my plan actually prefers before I assume the lower list price wins; 3) revisit each year because formularies and incentives change. I’m letting go of the idea that biosimilars are a magic “generic switch” that guarantees huge savings overnight. They’re more like a set of levers—science, regulation, and market incentives—that can produce meaningful savings when those levers align.

FAQ

1) Will a biosimilar always lower my copay?
Not always. If your plan sets a percent coinsurance and prefers the biosimilar, you’re likely to pay less. If the reference product is preferred due to contracting, your out-of-pocket may not change until the plan’s formulary changes (FTC PBM interim report).

2) What does “interchangeable” mean for me?
It’s an FDA designation that may allow pharmacy-level substitution according to state law. It doesn’t mean better safety or effectiveness—biosimilars already meet that bar (FDA basics; FDA 9 things).

3) I’m on an infusion drug under Medicare Part B. Does adoption change my bill?
It can. Qualifying biosimilars have a temporary add-on of ASP + 8% for providers, which can support availability, and lower allowed amounts can reduce your 20% coinsurance (CMS biosimilar FAQs).

4) How does the 2025 $2,000 Part D cap fit in?
It limits your annual out-of-pocket, which is a big deal. But month-to-month affordability still depends on formulary status and coinsurance. Biosimilar adoption can help you pay less before you hit that cap (CMS Part D cap fact sheet).

5) Where can I find neutral, official information?
Start with FDA explainers for definitions, CMS pages for Medicare payment and caps, and ASPE reports for big-picture spending effects (FDA basics; CMS biosimilar FAQs; ASPE 2025 analysis).

Sources & References

• FDA — Biosimilars Basics for Patients (2024)
• FDA — 9 Things to Know About Biosimilars (2024)
• CMS — Biosimilar FAQs and IRA Add-On (2022)
• CMS — 2025 Part D $2,000 Cap Fact Sheet
• HHS ASPE — Medicare Part B Biosimilars Issue Brief (2025)

This blog is a personal journal and for general information only. It is not a substitute for professional medical advice, diagnosis, or treatment, and it does not create a doctor–patient relationship. Always seek the advice of a licensed clinician for questions about your health. If you may be experiencing an emergency, call your local emergency number immediately (e.g., 911 [US], 119).