Biosimilar vs generic
A generic is an FDA-approved copy of a brand-name medicine, and it must work the same way as the original. A biosimilar is a very close, but not identical, version of a biologic, which is a medicine made from living cells. A compounded version is neither of these and is not FDA-approved.
For experts
In the US, a generic drug is approved under section 505(j) of the FD&C Act and must be the same as the brand-name drug in dosage, strength, stability, quality and the way it is taken, and must be shown to be therapeutically equivalent. A biosimilar is a biologic highly similar to an FDA-approved reference biologic with no clinically meaningful differences; biologics can be made of sugars, proteins, cells or tissues. For FDA, a protein is a defined amino acid polymer greater than 40 amino acids, so size affects which pathway applies (amylin, at 37 amino acids, is below that line). Compounded drugs are not generics, and biological products cannot be compounded under sections 503A or 503B.
Sources (4)
- 01Generic Drug FactsU.S. Food and Drug Administration · 2021-11-01 · accessed 2026-09-29
- 02Biosimilars Basics for PatientsU.S. Food and Drug Administration · 2024-08-01 · accessed 2026-09-29
- 03Compounding and the FDA: Questions and AnswersU.S. Food and Drug Administration · 2025-09-16 · accessed 2026-09-29
- 0421 CFR 600.3 - Definitions (including the definition of a protein)Electronic Code of Federal Regulations (eCFR), Office of the Federal Register · 2026-09-25 · accessed 2026-09-29