How biosimilars differ from generics

FDA's list of approved biosimilars had 90 entries when the agency last updated it on Oct. 28, 2026, according to its Biosimilar Product Information page¹. The first, a filgrastim product, was approved in March 2015. In 2025 alone, FDA approved 18 biosimilars and, by GxRadar's count of FDA's Drugs@FDA records², 648 original generic drug applications.

Those numbers are far apart because the two kinds of copies are far apart. People often call biosimilars "generic biologics," which is understandable and legally wrong. Generics and biosimilars are approved under different laws, held to different sameness standards and treated differently at the pharmacy counter.

It matters for spending. Biologics accounted for about 5 percent of US prescriptions but 51 percent of drug spending in 2024, FDA said in an October 2025 announcement³ of steps to speed biosimilar development.

Why a biologic cannot be copied exactly

A conventional drug such as metformin or atorvastatin is a small molecule made by chemical synthesis. A competitor can make the identical molecule, so a generic contains the same active ingredient as the brand.

A biologic is a large, intricate molecule, often a protein or antibody, produced in living cells. Small differences in the cell line, growth conditions or purification change the final product in subtle ways, and even the original maker's batches vary slightly. FDA's overview of biosimilar products⁴ says biologics generally cannot be copied exactly. A biosimilar is therefore held to a different test. It must be highly similar to the approved reference product⁵ and have no clinically meaningful differences in safety, purity or potency.

Two pathways side by side

For a small-molecule generic, the core scientific evidence is usually formulation work and a bioequivalence study, the subject of GxRadar's explainer on the 80-125 rule. The generic then earns a therapeutic equivalence code in the Orange Book, which is what lets pharmacists substitute it.

A biosimilar application rests mainly on analytical work: side-by-side laboratory comparisons of structure and biological function between the proposed product and many lots of the reference product. Developers have usually added pharmacokinetic studies in people and, for many products, a comparative efficacy trial in patients. FDA's biosimilar review and approval page⁶ calls comparative analytical data "the foundation of biosimilar development."

The law that created the pathway

Congress created the pathway in the Biologics Price Competition and Innovation Act of 2009 (BPCI Act), enacted on March 23, 2010, as part of the Patient Protection and Affordable Care Act⁷. It gave FDA an abbreviated route for biologics, modeled loosely on the generic system that the Hatch-Waxman Act set up in 1984. A biosimilar application cannot be submitted until four years after the reference product was first licensed, and FDA cannot make an approval effective until 12 years after that first licensure, as FDA's guidance on reference product exclusivity⁸ explains.

BPCI also moved some older protein drugs into the biologics framework. Insulins, human growth hormone and certain other proteins had historically been approved as ordinary drugs. On March 23, 2020, at the end of a 10-year transition, their approvals were deemed to be biologics licenses⁹. That change is why insulin copies now reach the market as biosimilars instead of generics.

How many FDA has approved, year by year

A few entries on FDA's list cover a pair of products with the same active ingredient sold under two names for different uses, so tallies that count each name separately come out higher. FDA put the total at 76 in October 2025. Biosimilars are also a growing share of FDA's biologic approvals, at 42 percent of biologics license approvals in fiscal 2025, up from 17 percent in fiscal 2016, according to the drug center's report on the state of pharmaceutical quality for FY2025¹⁰.

Approvals jumped in 2024 as more large antibody and protein brands lost exclusivity. On FDA's list¹, adalimumab and denosumab each have 10 entries, and ustekinumab and pegfilgrastim have eight each. Even so, FDA said in its October 2025 announcement³ that biosimilars held under 20 percent of their market and that only about 10 percent of biologics expected to lose patent protection over the following decade had a biosimilar in development.

Interchangeability and the switching-study rollback

Interchangeability is the feature that makes a biosimilar behave most like a generic at the pharmacy. An interchangeable biosimilar can be substituted for the reference product without the prescriber's intervention, depending on state pharmacy law, FDA explains⁵. A biosimilar without that designation generally has to be prescribed by name.

A company has to ask for the designation. FDA approved the first interchangeable biosimilar, an insulin glargine product, in July 2021. Developers seeking the label historically ran switching studies, in which patients alternate between the reference product and the biosimilar several times.

FDA has been taking those extra hurdles apart. A June 2024 draft guidance¹¹ said applicants could rely on an assessment of their analytical and clinical data in place of switching studies. On Oct. 29, 2025, FDA issued a draft guidance proposing that many biosimilars could skip comparative efficacy studies and rely on analytical testing instead. FDA said those trials take one to three years and cost about $24 million on average³, described them as having low sensitivity compared with analytical assessments, and said it now generally does not recommend switching studies. Both documents were issued as drafts, and draft guidance can change before it is finalized.

Names and labels

Every biosimilar carries a nonproprietary name with a four-letter suffix, such as insulin glargine-yfgn on FDA's list¹. The suffix distinguishes products that share an active ingredient, so pharmacy and medical records can show exactly which one a patient received. A pharmacist can say whether a dispensed product is the reference biologic, a biosimilar or an interchangeable biosimilar, and whether state law allowed a substitution.

New entries will appear on the same FDA page, which the agency updates as approvals come in; nine biosimilars had been added in 2026 through October. GxRadar's approvals tracker follows the generic side.