Amino Acid Count Determines Retatrutide's Biologic or Drug Classification

Dustin Robinson, Esq., CPA, founding partner of LumaLex Law, a full-service law firm representing clients across the telehealth and peptide supply chain, spoke to BioPharm International® about ongoing litigation over the regulatory classification of retatrutide, Eli Lilly and Company's (Lilly) investigational triple agonist peptide.

Robinson says the case centers on whether retatrutide's amino acid count places it above or below the 40-amino-acid threshold separating biologics from drugs, a distinction that determines 3 outcomes: market exclusivity length (12 years for biologics versus 5 for drugs), the pathway for competitor entry, and whether the molecule can legally be compounded. Biologics, he explains, can never be compounded under sections 503A or 503B of the Federal Food, Drug, and Cosmetic Act (FDCA).¹

How did an earlier court ruling land on retatrutide's regulatory classification?

An earlier court ruling held that only alpha amino acids count toward the 40-count threshold, upholding FDA’s measurement method. However, the court rejected FDA's use of that same method to determine whether the retatrutide molecule is analogous to a protein, reasoning that Robinson says is circular. Robinson emphasizes that this earlier ruling created a second, undefined legal pathway to biologic status before the US Court of Appeals for the Seventh Circuit held a hearing (Eli Lilly and Company v. Robert Kennedy, Jr.) on September 24, 2026.²

"Companies that get hurt in periods like this usually are the ones that treat legal uncertainty, like we have right now, as permission, and it's not," Robinson says.

Robinson emphasizes that retatrutide is not approved and is not on FDA's compounding list, meaning it cannot legally be compounded today regardless of how the Seventh Circuit rules. He notes that Lilly has filed lawsuits against compounders under state consumer protection and unfair competition laws rather than directly under the FDCA, a strategy he says exposes companies to private damages claims, legal fees, and injunctive relief.

About the speaker

Dustin Robinson, Esq., CPA, Founding Partner, LumaLex Law

Licensed in Florida as an attorney, certified public accountant, and real estate agent, Robinson brings a rare, fully integrated legal–financial–business perspective to every engagement. His practice focuses on corporate structuring, regulatory strategy, transactions, capital formation, and high-stakes commercial litigation for growth-stage and emerging-market companies across a wide range of industries.

References

1. FDA. Mixing, Diluting, or Repackaging Biological Products Outside the Scope of an Approved Biologics License Application: Guidance for Industry. Published January 2018. Accessed October 1, 2026. https://www.fda.gov/regulatory-information/search-fda-guidance-documents/mixing-diluting-or-repackaging-biological-products-outside-scope-approved-biologics-licensefda+1
2. Eli Lilly and Company v Robert Kennedy, Jr., No. 26-1301 (7th Cir argued September 24, 2026). Oral argument recording. US Court of Appeals for the Seventh Circuit. Accessed October 1, 2026. https://media.ca7.uscourts.gov/oralArguments/oar.jsp?caseyear=26&casenumber=1301&listCase=List+case