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Your Humira prescription just got swapped: what Medicare Part D biosimilars mean for Sioux Falls in 2026

Ten biosimilars now compete with Humira on price, and most 2026 Part D plans favor them. Here's what changed, and how to check your own formulary before it costs you.

Big Sioux Benefits Data Desk

Published August 10, 2026 · 12 min read · Sourced from HHS OIG, FDA.gov & CMS.gov

If a different-looking box showed up at the pharmacy where your Humira used to be, your Medicare Part D plan almost certainly switched its preferred formulary drug to one of ten FDA-approved Humira biosimilars — not a decision your doctor made behind your back. This happened to a lot more people in 2025 than in 2024, and it's continuing into 2026. Here's what a biosimilar actually is, why your plan made the switch, what it does and doesn't change about your cost, and exactly what to check before your next fill.

Every figure below comes from a source fetched directly for this article: the HHS Office of Inspector General's 2025 report on Part D biosimilar formulary coverage, the FDA's own list of approved biosimilar products, the Association for Accessible Medicines' 2025 savings report, and the CMS PY2026 Medicare Advantage landscape data behind this site's Sioux Falls plan roster. No invented numbers.

Where this fits in a bigger Part D story

This isn't an isolated pharmacy hiccup — it's one piece of a Part D program that got restructured for 2025 and 2026. The old "coverage gap" — the notorious donut hole — is gone, replaced by a single yearly out-of-pocket cap. For 2026 that cap sits at $2,100, with a maximum standard deductible of $615 before it. At the same time, the population of Part D enrollees taking high-cost specialty biologics — like adalimumab, ustekinumab, or etanercept — is exactly the group that cap was built to protect, because those are the prescriptions that used to blow past every prior limit.

Biosimilar competition and the new cap arrived on roughly the same timeline for a reason: a hard dollar ceiling on what beneficiaries pay only works long-term if the underlying drug costs the whole system pays are also under some downward pressure. That's the connection between the formulary letter you got in the mail and a federal cost structure most people never see spelled out. Understanding both halves — what changed in your formulary and what changed in your annual cap — is what actually answers "why did my prescription change, and does it matter."

What a biosimilar actually is

A biologic is a medicine grown in living cells rather than mixed from chemicals in a lab — Humira (adalimumab) is one, used for rheumatoid arthritis, psoriatic arthritis, Crohn's disease, ulcerative colitis, and several other inflammatory conditions. A biosimilar is a biologic the FDA has reviewed against the original ("reference") product and found to have no clinically meaningful difference in safety, purity, or potency. It isn't a chemical carbon copy — biologics are too complex for that — but the approval bar is the same rigor as the original drug's. The FDA requires biosimilar manufacturers to run analytical, animal, and human clinical studies specifically designed to rule out meaningful differences from the reference product before approval — it is a full review, not an expedited shortcut.

Some biosimilars also carry a second, stricter FDA designation called interchangeable. That status means a pharmacist can, in many states, substitute the biosimilar for the reference product at the counter without a new prescription — the same way a generic gets substituted for a brand pill. Not every Humira biosimilar has earned that designation, and state pharmacy law decides exactly how the substitution and any prescriber notice has to work. If you're not sure which applies to what's in your hand, ask the pharmacist directly.

A formulary is the list of drugs your specific Part D plan covers, and a tier is the pricing group a covered drug sits in on that list — lower tiers usually mean a lower copay, higher tiers usually mean higher coinsurance. Your plan's formulary, not your doctor's prescription pad, decides which name shows up at the pharmacy counter for a drug like adalimumab.

Humira's ten challengers

The FDA has approved ten biosimilars that reference Humira since 2016. Here is the complete, current list, pulled directly from the FDA's own biosimilar product database:

Source: FDA — Biosimilar Product Information, fetched August 2026. All ten reference Humira (adalimumab).

Ten different names, all reviewed against the same original drug. If your plan swapped you to one of these, that's what happened — a formulary decision among ten FDA-approved options, not a random substitution.

Why your plan made the switch, not your doctor

Part D plans move toward biosimilars because competition among ten manufacturers gives them more room to negotiate price than a single-source brand drug does. The shift has been fast. In 2024, only 65% of stand-alone Part D drug plans (PDPs) and 52% of Medicare Advantage drug plans (MAPD) covered even one Humira biosimilar. By the 2025 plan year, that jumped to 96% of PDPs and 88% of MAPD plans, according to the HHS Office of Inspector General.

Source: HHS Office of Inspector General, "Most Medicare Part D Plans' Formularies Included Humira Biosimilars for 2025" (report OEI-05-23-00520, issued May 2025). Figures are the share of plans covering at least one Humira biosimilar, by plan year.

The same OIG report found something worth knowing before you assume this is only good news: as of the 2025 plan year, 1% of PDP enrollees and 10% of Medicare Advantage drug-plan enrollees were in plans that covered Humira only, not any biosimilar — which, in effect, blocks the lower-cost option entirely for those members. Formulary coverage moved fast, but it isn't universal yet.

The savings behind the switch

Ten manufacturers competing to sell the same molecule tends to push prices down, and the national numbers back that up. According to the Association for Accessible Medicines' 2025 savings report, produced in partnership with the IQVIA Institute, generic and biosimilar medicines together saved the U.S. healthcare system $467 billion in 2024. Medicare specifically saved an estimated $142 billion that year — about $2,643 per beneficiary — across generics and biosimilars combined.

Biosimilars are the newer, smaller slice of that total, and they're growing fast: biosimilar competition alone is credited with $20.2 billion in savings in 2024, and $56.2 billion cumulatively since the first biosimilar reached the U.S. market in 2015. That's the financial pressure sitting behind your plan's decision to prefer a biosimilar over brand Humira — it isn't about your individual copay, it's about the total cost the plan (and by extension, the Medicare program and its premium payers) faces across every member taking the drug.

None of that is a promise about what happens to your specific bill. As the OIG data above shows, 99% of formularies keep brand and biosimilar on the same member-facing tier even after the switch — the savings mostly show up in what the plan pays the manufacturer, not necessarily in your copay. Your out-of-pocket protection in 2026 comes from the $2,100 cap, not from the biosimilar switch itself.

Source: Association for Accessible Medicines, 2025 U.S. Generic & Biosimilar Medicines Savings Report (with the IQVIA Institute), 2024 savings data.

What it costs if you don't check

Here's the surprising part: switching the drug name usually doesn't change your copay by itself. The OIG report found that 99% of formularies covering both Humira and a biosimilar placed them on the same cost-sharing tier — plans generally aren't using tier placement to push you toward the cheaper option or discourage the more expensive one. Nor are they typically applying different prior-authorization or step-therapy rules to one versus the other. In practical terms, the tier you're on likely didn't move; only the label on the box did.

What actually determines your bill is where adalimumab — brand or biosimilar — sits on your specific plan's formulary, and whether you've already hit your deductible for the year. Before 2026, a high-cost biologic like Humira, priced by AbbVie at roughly $90,000 a year as of 2022 figures cited by the OIG, could generate thousands of dollars in 20% coinsurance with no annual ceiling under some plan designs. That risk is now capped.

A worked example: what actually changes in your wallet

None of the figures below are a real person's bill — they're the published 2026 structural numbers, walked through in order, so you can see where a formulary switch does and doesn't touch your costs. The deductible is the amount you pay yourself before your plan starts sharing the cost; the coinsurance is the percentage you keep paying after that, until you hit your plan's limit.

1. Say your plan's drug deductible is on the higher end for 2026 — up to $615 under the standard structure. You pay that amount yourself first, regardless of whether your adalimumab prescription says Humira or a biosimilar name, because both usually sit on the same specialty tier.
2. After the deductible, your plan's coinsurance applies to each fill — the percentage is set by your specific plan and tier, not by the drug's brand status.
3. Your running total keeps climbing with each fill until it reaches the $2,100 out-of-pocket cap for 2026.
4. Once you cross that cap, Medicare picks up the rest of your covered drug costs for the remainder of the calendar year — no more coinsurance on covered prescriptions through December 31, 2026.

The upshot: switching from Humira to a biosimilar rarely moves any of these four numbers by itself, because the tier usually doesn't change. What the switch changes is which manufacturer gets paid, and it's part of why the overall drug-cost trend has room to bend — the math you personally do at the pharmacy counter is governed by your deductible, your tier, and the 2026 cap, not by the brand name on the box.

How a formulary switch actually reaches your mailbox

The process runs on a predictable federal timeline, not a surprise substitution at the counter:

Most formulary changes take effect at the start of the plan year, January 1, when your plan's whole drug list resets. If your plan wants to remove a covered drug — or move it to a more expensive tier — mid-year, federal rule requires it to mail you written notice first. That's your signal to call before you're standing at the pharmacy counter mid-refill.

Can your pharmacist swap you without calling your doctor?

Sometimes, yes — and that surprises people who assume every prescription change needs a new script. If the biosimilar you were given carries the FDA's interchangeable designation and your state's pharmacy substitution law allows it, a pharmacist can make that swap the same way they'd fill a generic for a brand-name pill, without contacting your prescriber first. Rules on whether and how quickly the pharmacist has to notify your doctor afterward vary by state pharmacy board. If you want to know exactly what applies to your prescription, ask your pharmacist directly which designation your specific biosimilar carries and what your state requires — it's a fair question, and pharmacists answer it every day.

If you'd rather stay on brand-name Humira specifically, your prescriber can request a formulary exception, typically citing medical necessity. Plans are required to offer this process. It isn't automatic and isn't guaranteed, but your doctor's office has almost certainly filed one before for a different drug and knows the drill.

The 2026 Sioux Falls plan picture

Minnehaha County (Sioux Falls) has 39,532 Medicare beneficiaries and five standard Medicare Advantage PPOs open to anyone with Medicare, each bundling drug coverage on its own formulary. The plans differ meaningfully on drug deductible even though they're priced in the same county — which matters for a specialty drug like adalimumab, because your deductible has to clear before your plan's coinsurance kicks in.

Source: CMS Medicare Advantage / Part D Landscape (PY2026) & CMS Medicare Advantage & Part D Star Ratings (2026), Minnehaha County, plan year 2026.

These are the plans we offer in the Sioux Falls area — Big Sioux Benefits does not offer every plan available in your area. Any information we provide is limited to those plans we do offer in your area; contact Medicare.gov, 1-800-MEDICARE, or your local State Health Insurance Program (SHIP) for information on all of your options. Beyond these five PPOs, the county also has Dual-Eligible Special Needs Plans and Medica Cost plans with their own formularies, covered in our all-plans guide.

Many of the conditions Humira and its biosimilars treat — rheumatoid arthritis, psoriatic arthritis — fall inside the broader category CDC data tracks locally: 22.9% of Minnehaha County adults report some form of arthritis, according to the CDC PLACES County Data (2023). That doesn't mean all of them are on a biologic — most arthritis is managed without one — but it's a large enough local population that a formulary switch like this touches real households across Sioux Falls, Brandon, and Tea every year.

What to do this week

You don't need to become a pharmacology expert to handle this. Here's the method, in order:

1. Call the number on your plan ID card and ask directly: is adalimumab covered, under what brand or biosimilar name, at what tier, and does it require prior authorization or step therapy this year? Write down who you spoke with and the date — plans occasionally give inconsistent answers, and a paper trail helps if you need to appeal later.
2. Ask your pharmacist which specific product you were given, whether it carries the FDA's interchangeable designation, and whether your doctor was notified. Pharmacists field this question often for high-cost biologics and can usually answer it on the spot.
3. Check your receipt against last year's — if the copay changed meaningfully, ask why; remember 99% of plans keep brand and biosimilar on the same tier, so a real jump is worth a call rather than an assumption.
4. If you want to stay on brand Humira, ask your prescriber's office to file a formulary exception request and be ready to explain why medically — a past reaction to a different product, or a treatment history that argues against switching, are the kinds of reasons plans look for.
5. Mark your Annual Notice of Change when it arrives by September 30 — it will show whether your 2027 formulary treats your drug differently again, and it's worth a slower read than the one most people give it before it lands in the recycling.

If you're on a different biologic

Humira isn't the only biologic that's seeing this pattern. FDA-approved biosimilars now exist for Stelara (ustekinumab), Enbrel (etanercept), Actemra (tocilizumab), Prolia and Xgeva (denosumab), Neulasta (pegfilgrastim), and several cancer and eye-disease biologics, per the same FDA product list referenced above. If your maintenance prescription is any of these, the same questions apply: call your plan, ask your pharmacist, and check your formulary before AEP.

The pattern tends to repeat itself: a reference biologic loses patent protection, several manufacturers bring FDA-approved biosimilars to market over the following years, and Part D formularies gradually shift preference toward the lower-cost competitors as more of them clear the FDA bar. If one biologic on your list hasn't seen a biosimilar yet, it likely will eventually — patent expirations are public information, and manufacturers announce biosimilar development pipelines years in advance. None of that requires you to track the pharmaceutical industry yourself. It just means the "check your formulary every fall" habit described below is worth keeping regardless of which specific biologic you take.

How we help

A drug cost review is exactly this: checking your actual prescriptions — not a generic drug list — against a specific plan's formulary and tier structure before you're locked into it for the year. We compare the plans we offer in the Sioux Falls area against your medications, confirm what's covered and at what tier, and flag anything that needs a formulary exception request. It costs nothing to ask, and carriers pay us, not you.

If you're new to Medicare or facing a biologic prescription for the first time near your 65th birthday, this same review is part of a turning-65 consultation — we walk your drug list against local plan formularies before you enroll, rather than after your first fill turns up a surprise. If you've been on Medicare for years and this is the first time a formulary switch has affected you, an annual coverage review catches this kind of change every fall, before the ANOC becomes background noise.

What to watch heading into 2027

1. Your 2027 Annual Notice of Change, arriving by September 30, 2026, will show whether your plan's formulary tier for your biologic shifts again.
2. More biosimilars may launch or gain interchangeable status for adalimumab and other biologics, which can reshuffle which product a plan prefers.
3. Watch for step-therapy rules requiring you to try a biosimilar before your plan will cover brand Humira, even with a prior authorization on file.
4. If you're on Stelara, Enbrel, Actemra, or another biologic with new biosimilar competition, check that formulary too — not just adalimumab's.
5. AEP runs October 15 through December 7, 2026 — your annual window to switch plans if your current formulary doesn't work for your prescriptions.

How we know all this: every figure in this article was pulled from a primary source fetched for this piece — the HHS Office of Inspector General's May 2025 report on Part D Humira biosimilar formulary coverage, the FDA's own current biosimilar product list, the Association for Accessible Medicines' 2025 savings report (with the IQVIA Institute), and the CMS PY2026 Medicare Advantage landscape and CDC PLACES county data behind this site's Sioux Falls figures, built by Strategic AI Architects. This is education, not medical or legal advice; confirm your own formulary, tier, and substitution rules with your plan, your pharmacist, and a licensed agent. We take no payment from any carrier or drug manufacturer to feature a plan or product.