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# Lilly Sues FDA Over Retatrutide Designation
- URL: https://www.fdaweb.com/lilly-sues-fda-over-retatrutide-designation/
- Published: 2024-09-25T12:00:00.000Z
- Updated: 2026-09-14T14:42:17.000Z
- Author: David McFarland
- Tags: Drugs, #legacy-id-D5157853

Lilly is suing FDA in an Indiana federal court to overturn the agency’s decision that the company’s investigational product retatrutide is a drug and not a biologic. It is one of the first suits to take advantage of the Supreme Court’s decision to scrap the decades-old “*Chevron* defense” that instructed courts to give deference to federal agencies’ interpretations of laws governing their actions.

The Lilly suit [says](http://www.fdaweb.com/download.php?file=lilly%5F9-2024.pdf) that under the Supreme Court’s *Loper Bright* ruling, a court must decide whether FDA has classified retatrutide properly and must not defer to the agency’s interpretation of the laws governing classification of drugs and biologics.

Lilly describes retatrutide as a product composed of 41 amino acids, 40 alpha amino acids and one other non-alpha amino acid. It says that as an adjunct to a healthy diet and physical activity, retatrutide has the potential to help adults manage obesity and other health conditions such as sleep apnea, knee pain, and Type 2 diabetes. It would be administered as a weekly injection.

The suit says FDA regulations define “protein” in part by the number of amino acids it contains (“greater than 40 amino acids in size”). It says the regulations say that a product qualifies as a protein, and thus is regulated as a biologic, if it **(1)** is an alpha amino acid polymer, **(2)** has a specific, defined sequence, and **(3)** is greater than 40 amino acids in size, counting the total number of amino acids.

“That aptly describes retatrutide,” Lilly says. However, the suit reports, FDA rejected the company’s request for designation as a biological product on the grounds that it is not “greater than 40 amino acids in size.” Lilly counters that 41 is plainly greater than 40\. It says FDA has changed its own requirements by saying that there must be greater than 40 alpha amino acids, even though that limitation does not appear in the regulation text.

The company also challenges FDA’s conclusion that retatrutide is not analogous to a protein because it has fewer than 41 alpha amino acids.

“This court should set aside FDA’s erroneous decision rejecting Lilly’s proposed classification of retatrutide and should order the agency to properly designate retatrutide as a biological product,” the suit says.

Designation of the product as a biologic is important to Lilly because it could get 12 years of market exclusivity rather than the five years given to drugs. Experts also say that because patents could last longer than exclusivity, a retatrutide biologic could be more successful in holding off generics. And, it could benefit from a provision in the Inflation Reduction Act making biologics subject to Medicare-negotiated pricing 13 years after approval, compared to nine years for small-molecule products.