A legal dispute between the FDA and Eli Lilly over whether the highly anticipated obesity candidate retatrutide is indeed a biologic has come to a head as the company prepares to submit the medicine for approval.
Is Eli Lilly’s up-and-coming obesity medicine a biologic? The FDA doesn’t appear to think so, and that opinion could shape how the company can file the potential blockbuster for approval and the years of market exclusivity that will follow.
A quiet legal war has been going on between Lilly and the FDA since September 2024, when the company sued the agency over the classification of retatrutide. The FDA determined that retatrutide is neither a protein nor a biological product, which would render it unapplicable for a biologics license application (BLA). Lilly would instead have to apply for approval of retatrutide as a drug and seek a new drug application (NDA), which has different requirements for evidence to support approval.
But most importantly, BLAs confer upon the drugmaker 12 years of market exclusivity. An NDA would provide Lilly with just five years. This distinction could be worth tens of billions to the company. The litigation remains unresolved, but the matter is coming to a head quickly as Lilly prepares to file retatrutide for approval.
A keen-eared analyst on Lilly’s second quarter earnings call on Wednesday noted that Dan Skovronsky, chief scientific and product officer, mentioned that the company will be 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,” CEO Dave Ricks, who spoke to the litigation, said on the call.
The FDA’s definition of a protein is any alpha amino acid polymer with 40 or more amino acids. Retatrutide has 41 amino acids, according to Lilly’s complaint. The FDA agreed that retatrutide is an alpha amino acid polymer and has a sequence of amino acids but said it does not have 40 or more alpha amino acids. The therapy was classified as a drug.
“But 41 is plainly ‘greater than 40,” Lilly argued. The decision to base the count on alpha amino acids goes against the agency’s own previous findings, the company asserted. “That limitation does not appear in the text, which distinguishes (including within the same sentence) between amino acids generally and the narrower category of alpha amino acids.”
The FDA defended its use of alpha amino acids for the 40 count during oral arguments in September 2025, arguing that history and regulatory precedents suggests that the correct count of alpha amino acids are what matters as to whether a medicine is a protein or not. The FDA’s regulatory text specifically says alpha amino acids, the agency noted.
Lilly has argued that retatrutide is “analogous to” a protein and should therefore be considered one.
“Tellingly, Eli Lilly points to no source at all that explicitly says what it wishes,” the lawyer argued on behalf of the agency.
The courts have provided a mixed decision so far on the matter, vacating the FDA’s biologics designation decision but returning the matter of whether the therapy is “analogous to a protein” back to the agency. Lilly has appealed the decision.
“Obviously, it’s active litigation, but we would hope to come to a conclusion with the FDA to support a BLA application,” Ricks said.
Lilly needs to resolve this issue—and soon. Future incretins could similarly face a regulatory rebuff over a few amino acids as well.
Ricks said the company has what it needs to submit a regulatory package for global registrations for retatrutide in obesity, obstructive sleep apnea and knee osteoarthritis pain. If the FDA rejects a BLA, the drug could be delayed.
Ricks added that Lilly is continuing to collect some manufacturing-related data for the product prior to the submission, which is targeted for the first quarter of 2027.
“While that’s going on, you could bet we’re in communication with the agency, and we’ll give an update to investors as there’s any progress on the filing status for retatrutide,” Ricks said.
Regulatory issues aside, Ricks said the data package for retatrutide is “super exciting.” The therapy has shown “unprecedented efficacy” over existing options, which include Novo Nordisk’s semaglutide franchise and Lilly’s own tirzepatide and oral Foundayo.
“We have a pretty large lead over any competitors with a triple-acting medicine,” Ricks said, “and we pursued a very interesting, I think, package of comorbidities in both the initial package and now in subsequent data that we’ll read out over the coming year or so.”
