Biosimilars Explained

Biologic medications represent some of the most effective treatments available for conditions including rheumatoid arthritis, Crohn’s disease, psoriasis, multiple sclerosis, and cancer. They are also among the most expensive drugs on the market. Biosimilars — medications developed to be highly similar to these reference biologics — offer the potential for comparable effectiveness at lower cost. Understanding how they work, what the FDA’s approval and interchangeability designations mean, and how pharmacist substitution operates prepares you to have informed conversations with your prescriber and pharmacist.

What makes a biologic different from a conventional drug

Conventional small-molecule drugs — most pills you take — are synthesized through controlled chemical processes and can be replicated exactly. Biological medications, or biologics, are fundamentally different. They are derived from living organisms — bacteria, yeast, or mammalian cells — through complex manufacturing processes. The resulting molecules are large, intricate proteins or antibodies that cannot be precisely reproduced even by the same manufacturer.

Because biologics are inherently variable at the molecular level and depend on proprietary cell lines and manufacturing conditions, no follow-on manufacturer can produce an exact copy. What they can do — and what the FDA’s biosimilar approval pathway exists to confirm — is produce a highly similar version with no clinically meaningful differences in safety, purity, or potency.

How the FDA approves biosimilars

The FDA approves biosimilars through a specialized regulatory pathway under the Biologics Price Competition and Innovation Act. Approval requires the applicant to demonstrate biosimilarity through a “totality of evidence” approach, which typically includes:

• Analytical studies: Detailed comparison of the biosimilar’s molecular structure, biological activity, and physical properties to the reference product
• Animal or nonclinical studies: Toxicology comparisons (often streamlined if the analytical data is strong)
• Human pharmacology studies: Clinical trials comparing pharmacokinetics (absorption and elimination) and pharmacodynamics (biological effect) in human subjects
• Clinical comparative studies: Trials in one or more of the reference product’s approved indications to confirm no clinically meaningful differences in efficacy and safety

A biosimilar approval means the FDA has determined that available data demonstrate the product is as safe and effective as the reference biologic for its approved indications. The standard explicitly requires “no clinically meaningful differences” — it does not require molecular identity, which is impossible with biological molecules.

Biosimilars versus interchangeable biosimilars

FDA biosimilar approval comes in two tiers:

Designation	What it means	Pharmacist substitution permitted?
Biosimilar	Highly similar; no clinically meaningful differences	Only with prescriber authorization (in most states)
Interchangeable biosimilar	Meets biosimilar standard plus additional evidence that switching will not increase risk	Yes, in most states (subject to state pharmacy laws and notification requirements)

Interchangeability requires the manufacturer to submit additional data — typically switching studies — demonstrating that alternating between the biosimilar and the reference product does not produce a greater risk of adverse outcomes than staying on one product. The FDA publishes a list of interchangeable products on its Purple Book database.

This distinction matters for patients because it determines whether your pharmacist can substitute the biosimilar without your prescriber’s explicit approval.

Documents and terms you’ll see

When dealing with biologic and biosimilar prescriptions, these terms appear frequently in plan communications, pharmacy notifications, and FDA materials:

• Biosimilar — a biologic product approved by the FDA as highly similar to a reference product; listed in the FDA’s Purple Book with its approval status and interchangeability designation
• Reference product — the original brand-name biologic; the benchmark to which a biosimilar is compared during the approval process
• Interchangeable biosimilar — a biosimilar meeting the higher FDA standard that permits pharmacist substitution in states that have adopted the relevant laws
• Biologic — the broad category of medications derived from living organisms; biologics are subject to a different approval pathway than small-molecule drugs

How biosimilar pricing works in practice

Biosimilar list prices are typically 15–35 percent below the reference product’s list price, and the savings can be considerably larger for some products. However, the price a patient actually pays is often shaped more by formulary design than by list price.

Prescription drug formularies (your plan’s covered drug lists) place biosimilars and reference products on tiers that determine your cost-sharing. In some plan designs, the biosimilar is placed on a lower tier with a lower copay than the reference product — incentivizing switching. In others, the reference product may be heavily rebated by the manufacturer, resulting in a lower net cost to the insurer, which can lead the insurer to favor the reference product with better tier placement.

If you are starting a high-cost biologic, it is worth asking your insurer’s pharmacy benefit manager or your pharmacist:

• Is a biosimilar available for this drug?
• What tier is each option on my formulary?
• What is my out-of-pocket cost for each?

Manufacturer copay assistance cards for brand-name biologics, and patient assistance programs for biosimilars, may also affect your actual cost. These programs typically have eligibility restrictions (they often cannot be used by Medicare or Medicaid beneficiaries) — verify eligibility before relying on them.

What pharmacist substitution means for you

In states that permit it, a pharmacist may substitute an interchangeable biosimilar for the prescribed reference product — or vice versa — without going back to the prescriber, subject to notification requirements that vary by state. Most states require the pharmacist to inform you of the substitution before dispensing and may require them to notify your prescriber within a defined window.

If you have a clinical reason to stay on the specific product your prescriber has prescribed — for example, you are stable on it, switching has caused problems before, or your prescriber has a clinical rationale for the specific product — communicate this to both your prescriber and pharmacist. Prescribers can indicate “dispense as written” to prevent substitution. Conversely, if you would like to explore a biosimilar to reduce costs, raise this with your prescriber, who can confirm whether the switch is appropriate for your situation.

The prescriptions, generics, and discount programs guide covers the broader landscape of formulary design, tier structures, and cost-reduction strategies that apply to both conventional drugs and biologics.