Why Isn't Retatrutide Approved Yet?

Eli Lilly has not sought FDA approval for retatrutide, despite strong trial results, because it is fighting to have the drug classified as a biologic rather than a conventional medicine. That classification could give Lilly 12 years of FDA exclusivity instead of five and make it harder for competitors to sell biosimilar versions; biologics also cannot be compounded by pharmacies. The added protection could help Lilly restrict the grey-market peptide sales that have persisted even after the shortage of its related drug tirzepatide ended. The delay costs Lilly potential sales, but the company is betting that longer market control will be worth the wait.

The dispute turns on whether retatrutide meets the FDA’s definition of a protein: a polymer of more than 40 alpha amino acids. Its main chain has 39; Lilly argues that two components in a side branch should count toward the total, while the FDA says they do not. A district court upheld the FDA’s finding that retatrutide is not a protein but said the agency should consider whether it might still be analogous to one. Lilly appealed, and a Seventh Circuit ruling is expected. If Lilly wins, it plans to file a biologics application in early 2027. If it loses, it could pursue further litigation or apply as a conventional drug; the piece suggests approval might then come as late as 2029.