Retatrutide: general

Retatrutide is an investigational drug from Eli Lilly, also known by its development code LY3437943. It is a peptide that acts at three hormone receptors at once: the phase 2 trial describes it as “an agonist of the glucose-dependent insulinotropic polypeptide, glucagon-like peptide 1, and glucagon receptors”.[1] That third receptor, glucagon, is what separates it from semaglutide (GLP-1 only) and tirzepatide (GIP and GLP-1).

What the trials found

In the published phase 2 obesity trial, the investigators wrote: “We enrolled 338 adults”.[1] Their conclusion was that “In adults with obesity, retatrutide treatment for 48 weeks resulted in substantial reductions in body weight”, and that “The most common adverse events in the retatrutide groups were gastrointestinal”.[1] Lilly has since reported positive phase 3 results in its own news releases, and states that “Lilly plans to submit a Biologics License Application (BLA) for retatrutide to FDA in Q1 2027”.[2] Those phase 3 figures are the company's topline announcements, not yet peer-reviewed papers.[2]

Status

It is not an approved medicine. In its October 2026 lawsuit against a seller, Lilly states that “no retatrutide medicine has yet been approved by FDA or any other regulatory agency in the world”.[3] The FDA says retatrutide and similar unapproved products “have not been found safe and effective for any condition”.[4] The legal section covers what that means country by country.

What is sold under the name

Anything sold as retatrutide today is not Lilly's drug. The FDA describes products falsely labelled for research: “These products have been sold directly to consumers for human use with dosing instructions”, and warns that such products “could contain too little, too much or no active ingredient at all”.[4] Testing reported by ABC News found much the same: one laboratory said “it has tested 18 samples of counterfeit retatrutide this year with only one matching its label claim”.[5] In Australia, Victoria's health department reported that “there have been six cases of acute liver injury in Victoria in people who have used an unapproved peptide product, labelled as Retatrutide”, and suspects a contaminant.[6]

Read more on this site

• Retatrutide from a research vial: what the trials found, what tested vials held, and the warning signs.
• Lilly v. the retatrutide sellers: the lawsuits against sellers and where each case stands.
• A regulated peptide market: what the proposed federal peptide policy may and may not change.

References

1. Triple-Hormone-Receptor Agonist Retatrutide for Obesity: A Phase 2 Trial (Jastreboff et al., N Engl J Med 2023;389:514-526) — PubMed (New England Journal of Medicine)
2. Lilly's triple agonist, retatrutide, successful in two additional Phase 3 obesity trials (news release, July 23, 2026), Wayback capture of 12 October 2026 — Eli Lilly and Company
3. Eli Lilly and Company v. American Peptides LLC, No. 5:26-cv-04146 (W.D. La.), Complaint, filed 10/08/26 — US District Court, via CourtListener RECAP
4. FDA's Concerns with Unapproved GLP-1 Drugs Used for Weight Loss (content current as of 10/01/2026), Wayback capture of 19 October 2026 — US Food and Drug Administration
5. New testing of black-market peptides reveals dangerous dosing levels (Rachel Carbonell, Caitlyn Gribbin and Andi Yu for ABC News, 28 August 2026) — RNZ
6. Toxicity linked to unapproved peptide product labelled Retatrutide (health alert, 19 June 2026) — Department of Health, Victoria, Australia