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What are biosimilar drugs?

Medically reviewed by Leigh Ann Anderson, PharmD. Last updated on March 10, 2024.

Official answer



A biosimilar is a biological product that is similar to a reference biologic (usually the original product) and for which there are no clinically meaningful differences in terms of safety, purity, and potency.

  • Let’s look at an example: Amjevita (adalimumab-atto) was the first biosimilar approved for Humira (adalimumab) used to treat rheumatoid arthritis and psoriasis, among other uses.
  • In this case, Humira is the reference (original) product that fulfilled the adalimumab clinical studies and was approved by the FDA.

Biosimilars are expected to help the U.S. healthcare system and consumers save money, although biosimilar products are usually still very expensive. According to the RAND Corporation, biosimilars could help save the U.S. health system close to $54 billion on biologics spending through 2026.

As of March 10, 2024, there are 49 biosimilars, including 10 that are interchangeable products approved by the U.S. Food and Drug Administration (FDA). The most recent biosimilars approvals in 2024 are Tyenne (tocilizumab-aazg), a biosimilar to Actemra, Wyost (denosumab-bbdz), designated interchangeable with Xgeva, and Jubbonti (denosumab-bbdz), designated interchangeable with Prolia.

  • Interchangeable biosimilar products may be substituted by a pharmacist without the intervention of the prescriber of the reference product.
  • A healthcare provider also can prescribe an interchangeable product similar to how they would prescribe a biosimilar or a reference product. Pharmacy laws may vary by state.

What is a biologic?

If a biosimilar is a biologic, then what is a biologic? Biological products can include a wide range of products including:

  • vaccines
  • blood components
  • gene therapy
  • tissues
  • proteins, like monoclonal antibodies and cell signaling proteins.

Unlike most chemically-derived small-molecule drugs, biological products are generally derived from a living organism, such as humans, animals, microorganisms or yeast. Clinically, they are used to treat patients with cancer, kidney diseases and autoimmune diseases, such as rheumatoid arthritis and Crohn's disease.

For example, Enbrel (etanercept) or Humira (adalimumab) are referred to as “large-molecule” drugs because they are larger and more complex in structure than small-molecule drugs (like ibuprofen).

Biologic products are very expensive, often in the tens-of-thousands of dollars per year, due to costs linked to complicated development and manufacturing. Often, patients will need to access these medications through a specialty pharmacy.

Are biosimilars a generic?

A biosimilar is not considered a “generic” in the same way that a traditional, small molecule drug (for example: ibuprofen or acetaminophen) is determined to be a generic. Biosimilars are "similar" because they are biologics that do not have to be exact copies of the active ingredient, as with small-molecule drug generics.

In 2010, the U.S. signed into law an abbreviated approval pathway for biologics to encourage production, create competition, increase treatment options and reduce healthcare costs. Under the new law, a biological product may be demonstrated to be “biosimilar” if data show that the product is “highly similar” to an already-approved biological product.

The law, known as the Biologics Price Competition and Innovation Act of 2009 (BPCI Act), aligns with the FDA’s long standing-policy of permitting appropriate reliance on drug science that has already been established, thereby saving time, resources and unnecessary duplication of animal testing or human clinical trials.

How are biosimilars named?

In January 2017 the FDA issued a guidance on naming conventions for biosimilars. According to the guidance the nonproprietary name designated "will be a proper name that is a combination of the core name and a distinguishing suffix that is devoid of meaning and composed of four lowercase letters."

In the current naming convention, the FDA has designated guidelines for approved biosimilar nonproprietary names that incorporate four lowercase letters (a suffix).

FDA has stated drug companies can propose up to 10 suffixes for each new biosimilar.
Currently, the licensed biosimilars have gained the unique 4-letter suffix, but the older reference product may not have a suffix, for example; for example: adalimumab (Humira).

Some older biosimilars are linked with the manufacturer (filgrastim-'sndz' for Sandoz), and some random (infliximab-dyyb); going forward they will be random and not linked with the manufacturer's name.

Related Questions

Can pharmacists automatically substitute a biosimilar for a brand name biologic?

Yes, but ONLY for FDA-approved biological products specifically designated as interchangeable, as found in The Purple Book database. According to the FDA, automatic substitution can happen once a product is deemed interchangeable.

If the product has been determined to be interchangeable, then it is "biosimilar" to the reference product AND will produce the same clinical result as the reference product in any given patient. Interchangeable also means the original biologic and the new biosimilar can be switched back and forth in a patient without a risk of diminished safety or efficacy.

However, if needed, biosimilars can be dispensed by a pharmacist in place of another biological product if a physician or other healthcare professional specifically prescribes the biosimilar product by name.

Which interchangeable biosimilars are approved in the U.S.?

Reference products and their interchangeable biosimilars approved by the FDA as of March 5, 2024 are:

Interchangeable products for Humira (adalimumab):

Interchangeable products for Lantus (insulin glargine):

Interchangeable products for Lucentis (ranibizumab):

Interchangeable products for Prolia (denosumab)

  • Jubbonti (denosumab-bbdz)

Interchangeable products for Stelara (ustekinumab)

Interchangeable products for Xgeva (denosumab)

  • Wyost (denosumab-bbdz)

Related: Table of biosimilar products currently approved in the U.S.

If you have questions, ask your pharmacist. Pharmacists will know which biological products are approved as interchangeable by the FDA, and can check The Purple Book database to find these products.

What is the Purple Book?

The Purple Book database is the go-to resource for pharmacists and other health care providers interested in making an interchange between a reference biologic and a biosimilar. It is found online on the FDA website.

Similar to The Orange Book used to compare generic products to their brand name counterparts, The Purple Book database has been developed by the FDA to list each reference biological product and the corresponding biosimilar and interchangeable biological product.

Biosimilars designated as interchangeable will have no clinically important differences from the original product. Variation in formulation, delivery device, indications, and routes of administration may be acceptable.

Additional biosimilar product information can also be accessed on the FDA website.


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