Biosimilar Switching Guide 2026: Humira, Stelara, and Enbrel

Humira (adalimumab), Stelara (ustekinumab), and Enbrel (etanercept) are three of the most prescribed biologic drugs in the United States for autoimmune conditions including rheumatoid arthritis, plaque psoriasis, psoriatic arthritis, Crohn's disease, and ulcerative colitis. All three are self-administered subcutaneous injections, typically covered under Medicare Part D or commercial pharmacy benefits. Together, these three biologics account for a large share of total US prescription drug spending, which is why the Inflation Reduction Act of 2022 selected Stelara and Enbrel for its first round of Medicare price negotiation, and why Humira's biosimilar market has drawn intense regulatory attention.

For 2026, Medicare Part D patients on these biologics have three distinct cost-reduction pathways. Patients on Stelara or Enbrel receive the IRA Maximum Fair Price automatically through any Part D plan, with their total annual out-of-pocket cost capped at $2,100 across all Part D drugs. Patients on Humira can switch to one of seven FDA-designated interchangeable biosimilars, which pharmacists may substitute without requiring a new prescription under most state laws, reducing the monthly cost from roughly $6,900 to as low as $1,015. Patients without Medicare or commercial insurance can apply to manufacturer patient assistance programs, though AbbVie's program for Humira is closing to new applicants effective July 1, 2026. Patients whose plans impose formulary tier requirements should request a formulary exception or step-therapy override if they cannot afford the assigned cost share.

Prescribers and patients should understand that biosimilar and generic are not synonymous in the biologic world. A biosimilar is a biological product that is highly similar to and has no clinically meaningful differences from an existing FDA-approved reference product. An interchangeable biosimilar meets the additional FDA standard for pharmacy-level substitution without a new prescriber authorization. FDA approval means a biosimilar is as safe and effective as the reference biologic for all approved indications. Patients with concerns about switching should discuss the scientific evidence with their rheumatologist or gastroenterologist; real-world data from 2025 and 2026 shows that most patients who switch to an adalimumab biosimilar maintain clinical response. However, among those who switched, approximately 13 percent eventually returned to the originator Humira in real-world studies, underscoring the importance of clinical monitoring after any formulary-driven switch.

What Biosimilar Switching Guide Costs by Point of Pay (2026)

The price you pay depends almost entirely on WHERE you pay. The same biosimilar switching guide can cost many times more at a hospital than at your local pharmacy:

Why Hospitals Charge So Much

All three reference biologics (Humira, Stelara, Enbrel) carry list prices far above their actual acquisition costs to hospitals and health systems, which typically purchase biologics at substantial discounts through 340B pricing, group purchasing organizations, or direct manufacturer contracts. When a biologic appears on an inpatient hospital bill at the undiscounted list price, the gap between the acquisition cost and the billed charge can be enormous. Stelara's IV induction dose for Crohn's disease, for example, has appeared on hospital itemized bills at $15,000 to $35,000, even when the actual acquisition cost under 340B is a fraction of that.

Biologics administered in an outpatient hospital infusion center or physician office can be billed under Medicare Part B rather than Part D. Part B reimbursement for adalimumab uses HCPCS code J0139 (per 1 mg) at the ASP plus 6 percent. Ustekinumab IV infusion uses J3358. Etanercept uses J1438. When these drugs are billed under Part B, the patient's Part B deductible of $283 in 2026 and the standard 20 percent coinsurance apply. For high-dose induction therapies like Stelara IV, 20 percent coinsurance on a $15,000 infusion equals $3,000 out of pocket before Medigap coverage. Patients receiving infused biologics should confirm their coverage path (Part B vs. Part D) before each administration.

Three structural factors drive biologic hospital markups above retail rates. First, hospital pharmacies purchase drugs at acquisition cost but bill at the Chargemaster rate, which may be set at list price or higher. Second, infusion center facility fees are layered on top of the drug charge, sometimes doubling the total bill. Third, coding errors such as billing adalimumab under an outdated or incorrect J-code can cause claim rejection and re-billing at a higher rate. Patients who receive an unexpected bill for a biologic should request an itemized statement with the NDC number and the HCPCS code, then compare the billed drug cost to the published ASP for that quarter.

HCPCS J-Codes: What Appears on Your Bill

All three biologics have HCPCS Level II J-codes used when the drug is administered in a clinical setting (physician office, infusion center, or hospital outpatient department) and billed under Medicare Part B. These codes changed recently for adalimumab (J0139 replaced J0135 effective January 2025). Using the wrong J-code is the most common billing error for adalimumab in 2026.

Patient Assistance Programs

Manufacturer patient assistance programs (PAPs) for biologics are among the most valuable cost-reduction tools for uninsured and underinsured patients. However, the landscape shifted in 2026. AbbVie's myAbbVie Assist program for Humira is closing to new applicants on July 1, 2026, directing patients toward adalimumab biosimilars (many of which have their own PAPs). Patients with Medicare, Medicaid, TRICARE, or VA benefits cannot use manufacturer copay savings cards (federal anti-kickback statute, 42 U.S.C. § 1320a-7b); the income-based PAPs listed below are the correct option for those patients.

Medicare Part D

Medicare Part D covers all three of these biologics for their FDA-approved indications. For 2026, the annual out-of-pocket cap across all Part D drugs combined is $2,100, set by the Inflation Reduction Act of 2022. Stelara and Enbrel beneficiaries automatically receive the IRA Maximum Fair Price through any Part D plan: $4,695 for Stelara and $2,355 for Enbrel. A patient on Stelara whose monthly cost under the MFP is $4,695 would hit the $2,100 annual cap before the end of January and pay $0 for the remainder of 2026. Medicare Part D patients on Humira should ask their plan about formulary tier placement for adalimumab biosimilars, as many major Part D plans have moved brand-name Humira to non-preferred or excluded tier in 2026.

Medicare Part D formulary tier placement for biosimilars is a key issue in 2026. CMS has required Part D plans to include biosimilar alternatives when they exist, but formulary tiering decisions affect what the patient actually pays at the pharmacy counter. A biosimilar placed on a lower formulary tier than the reference biologic effectively steers patients toward the lower-cost option. Patients who are stable on a reference biologic and whose plan changes the formulary tier mid-year should request a formulary exception based on medical necessity to maintain access to their existing therapy. The Medicare Part D formulary exception process requires a prescriber attestation that the preferred biosimilar is not clinically appropriate for the patient.

Medicare beneficiaries on these biologics may also qualify for Medicare Low-Income Subsidy (Extra Help), which can reduce or eliminate Part D cost-sharing for all covered drugs including biologics. Patients with incomes up to 150 percent of the federal poverty level and limited assets may qualify for full Low-Income Subsidy, capping their cost share at $11.20 per covered drug in 2026. Part D plans cannot deny coverage for an IRA-negotiated drug (Stelara, Enbrel) based on prior authorization requirements alone for the IRA-negotiated indication.

Common Biosimilar Switching Guide Billing Errors

Biologic drugs generate some of the most complex billing scenarios in US healthcare. If you receive a bill for Humira, Stelara, or Enbrel that seems far above your expected cost share, check for these errors before paying:

• Adalimumab billed under obsolete J0135 code (deleted January 2025) instead of J0139. Any claim using J0135 after December 31, 2024, is a coding error and may be rejected by Medicare or commercial insurance, then re-billed at the full retail price.
• Brand Humira billed under Stelara J-codes or vice versa. Confirm the HCPCS code on your EOB matches the actual drug dispensed. J0139 = adalimumab only; J3357/J3358 = ustekinumab only; J1438 = etanercept only.
• IRA Maximum Fair Price not applied for Medicare Part D patients on Stelara or Enbrel. Since January 1, 2026, every Part D plan must apply the IRA MFP. If your pharmacy statement shows a cost above $4,695 for a 30-day Stelara supply or above $2,355 for Enbrel, call your plan immediately.
• Manufacturer copay card applied to a Medicare, Medicaid, or TRICARE claim. This is illegal under the anti-kickback statute and can trigger an audit. If a pharmacist tries to apply an AbbVie, Janssen, or Amgen savings card to a government-insured claim, refuse and ask for the PAP instead.
• Biologic billed under medical benefit (Part B) when it should be under pharmacy benefit (Part D), or vice versa. Self-injected biologics taken at home are Part D. Provider-administered biologics in a clinical setting are Part B. The wrong pathway changes both the coverage rules and the cost share.
• Annual Part D OOP cap exceeded but $0 rate not applied. In 2026, once you have paid $2,100 in total Part D out-of-pocket spending, you owe $0 for covered drugs for the rest of the calendar year. If you are billed a copay after hitting the $2,100 cap, dispute the charge with your plan and the pharmacy.

Frequently Asked Questions