As Eli Lilly prepares to file retatrutide for FDA approval in the first quarter of 2027, a long-running legal dispute over how the drug should be classified — biologic or small-molecule drug — is coming to a head, with billions of dollars in potential market exclusivity at stake (BioSpace).
The litigation dates to September 2024, when Lilly sued the FDA over its determination that retatrutide is neither a protein nor a biological product. If the drug is deemed a biologic, Lilly could pursue a Biologics License Application (BLA), which confers 12 years of market exclusivity in the U.S. A traditional New Drug Application (NDA) would provide only five years — a distinction analysts say could be worth tens of billions of dollars over the drug’s commercial life.
The 40-amino-acid question
The dispute turns on the FDA’s definition of a protein: any alpha amino acid polymer with 40 or more amino acids. Retatrutide has 41 amino acids, according to Lilly’s complaint — but the FDA agrees it is an alpha amino acid polymer with a sequence of amino acids while arguing it does not have 40 or more alpha amino acids, and classified the therapy as a drug.
Lilly’s response: “But 41 is plainly ‘greater than 40.’” The company argues the agency’s decision to base the count on alpha amino acids contradicts its own previous findings and its regulatory text, which “distinguishes (including within the same sentence) between amino acids generally and the narrower category of alpha amino acids.” Lilly also contends retatrutide is “analogous to a protein” and should be treated as one.
The FDA has defended its reading, noting its regulatory text specifically says alpha amino acids. During oral arguments in September 2025, an agency lawyer pressed the point: “Tellingly, Eli Lilly points to no source at all that explicitly says what it wishes.”
The courts have so far produced a mixed result — vacating the FDA’s biologics designation decision but returning the question of whether the therapy is “analogous to a protein” to the agency. Lilly has appealed.
”We would hope to come to a conclusion”
On Lilly’s second-quarter earnings call on August 5, CEO Dave Ricks acknowledged the active litigation while confirming the company is pursuing a BLA. “We’ve been pursuing this for a little while because we believe retatrutide is a biologic application, both in terms of [the] amino acid count rule as well as analogous to a protein, so that’s our position,” Ricks said. “Obviously, it’s active litigation, but we would hope to come to a conclusion with the FDA to support a BLA application.”
BioSpace notes that if the FDA rejects a BLA, the drug could be delayed — and that the outcome carries implications beyond retatrutide: “Future incretins could similarly face a regulatory rebuff over a few amino acids as well.”
Canadian context
For Canadians, the classification fight matters even though it is a U.S. proceeding. Health Canada operates its own regulatory framework that distinguishes biologic drugs from small molecules, with different submission pathways, review requirements, and post-market obligations — and a biologic designation for retatrutide in the U.S. would influence how the drug is handled under Canada’s biologics and biosimilar regimes.
The exclusivity gap is also relevant to Canadian access. Longer U.S. market exclusivity for a biologic means more time before biosimilar competitors can enter — which in turn affects the pricing environment Canadian public and private payers will face when the drug eventually reaches the Canadian market. As this site has covered, Health Canada review would likely follow the U.S. filing by months, with a potential Canadian approval in late 2027 or early 2028.
Retatrutide remains an investigational drug not approved by Health Canada or the FDA. Canadians should continue to rely on approved treatments and legitimate clinical trial or Special Access Programme pathways.