Short answer: Retatrutide (LY3437943) is an investigational medicine from Eli Lilly that stimulates the GIP, GLP-1 and glucagon receptors together. Its first Phase 3 results were published in September 2026: in the TRIUMPH-1 trial (NEJM), mean body weight fell by 25.0% at 80 weeks in the 12 mg group, against 3.9% with placebo. Even so, as of October 2026 retatrutide has not been approved by the FDA, the EMA, the MHRA or any other regulator and is not sold on prescription anywhere. "Retatrutide" sold online is not legal and its contents are unknown; buying or using it is strongly advised against.

Key takeaways

  • Retatrutide is an investigational triple agonist and has not reached approval anywhere.
  • TRIUMPH-1 (NEJM, September 2026): in 2,339 adults with obesity and without diabetes, mean weight change at 80 weeks was a fall of 17.6% with 4 mg, 23.7% with 9 mg and 25.0% with 12 mg, against 3.9% with placebo.
  • TRIUMPH-2 (The Lancet, October 2026): in 1,152 adults with type 2 diabetes, mean weight fell by 18.8% with 12 mg and 5.1% with placebo at 80 weeks.
  • The most common side effects were gastrointestinal. In TRIUMPH-2, dysaesthesia (abnormal skin sensation) and low blood pressure were reported more often with retatrutide than with placebo.
  • These are trial averages and do not predict what any one person will lose.
  • No approved retatrutide product exists. Check FDA, EMA and MHRA announcements for its current status.

This page is for general information only and does not replace medical advice. Retatrutide is not an approved medicine; the results below come from clinical trials and should not be read as a treatment recommendation. Speak to your GP or prescriber about decisions on weight management.

What is retatrutide and how does it work?

GLP-1 medicines in use today act on one or two hormone receptors:

  • Wegovy and Ozempic (semaglutide): stimulate only the GLP-1 receptor.
  • Mounjaro and Zepbound (tirzepatide): stimulate the GIP and GLP-1 receptors.
  • Retatrutide: stimulates the GIP, GLP-1 and glucagon receptors (a triple agonist).

What does adding the glucagon receptor change?

The role of glucagon receptor activity in energy use and liver fat is being studied. How much it adds to the GIP and GLP-1 effect in people, and how safe it is in the long term, are the questions the Phase 3 trials set out to answer.

Phase 3 results: the TRIUMPH programme

The first two trials of Lilly's TRIUMPH Phase 3 programme were published on 29 September 2026. In both, participants received once-weekly retatrutide 4 mg, 9 mg or 12 mg, or placebo, for 80 weeks. Results were reported with an analysis that counts every participant, including those who stopped treatment (the treatment-regimen estimand).

Trial Participants Mean weight change at week 80 Publication
TRIUMPH-1 2,339 adults with obesity and without diabetes 4 mg: down 17.6%; 9 mg: 23.7%; 12 mg: 25.0%; placebo: 3.9% NEJM, September 2026
TRIUMPH-2 1,152 adults with type 2 diabetes and overweight or obesity 4 mg: down 11.9%; 9 mg: 16.8%; 12 mg: 18.8%; placebo: 5.1% The Lancet, October 2026

TRIUMPH-1 also looked at knee osteoarthritis pain and obstructive sleep apnoea in subgroups of participants, and reported greater improvement with retatrutide than with placebo in both. TRIUMPH-2 also reported improved blood sugar control.

On safety, the most common side effects were gastrointestinal, such as nausea and diarrhoea. In TRIUMPH-2, low blood pressure and dysaesthesia were reported more often with retatrutide than with placebo. In the same trial, permanent discontinuation because of adverse events or death was 12% with 9 mg, 8% with 12 mg, 4% with 4 mg and 5% with placebo.

Company press releases may quote higher figures based on a different analysis (one that estimates the effect as if everyone had stayed on treatment). This page reports the primary analyses published in peer-reviewed journals.

How to read these numbers

These are averages across large trial groups. Individual results vary widely, and they do not predict what any one person will lose. Participants were followed regularly by trial doctors. Because these trials did not compare retatrutide directly with another medicine, setting their numbers beside Mounjaro or Wegovy trial results is not a valid comparison.

The earlier study: NEJM Phase 2 (2023)

Before Phase 3, a Phase 2 trial published in NEJM in 2023 followed 338 adults with a BMI of 30 or above for 48 weeks. In the highest-dose group, 12 mg, mean weight change was a fall of 24.2%. A separate Phase 2a analysis (Nature Medicine, 2024) looked at liver fat in participants who had fatty liver at the start.

Approval status (October 2026)

Stage Status
Phase 2 Completed, published in NEJM in 2023
Phase 3 (TRIUMPH) First results published in NEJM and The Lancet in September and October 2026; other trials ongoing
FDA and EMA applications Lilly said on 29 September 2026 that it plans to submit to the FDA in the first quarter of 2027
Prescription sale Not approved in any country

For a medicine to reach pharmacies, regulators must review and approve the Phase 3 evidence. That review usually takes months after an application is filed, so no firm date can be given.

Products in vial or powder form are being sold on websites, on social media and in messaging groups under names such as "retatrutide peptide" or "research chemical".

What to know about these products:

  1. No licence and no legal sale: No approved retatrutide medicine exists in any country. In trials the drug is given only to participants, under medical supervision.
  2. Unknown contents: These products are unregulated. Their contents, purity, sterility and dose are unknown, so their safety is unknown too.
  3. Heart rate and other risks: Glucagon receptor activity can raise heart rate. Long-term safety data are not yet complete.
  4. Legal liability: Selling unlicensed medicines is illegal in the UK and most other countries.

Where to follow the approval process

  • United States: FDA press announcements.
  • Europe: EMA CHMP meeting highlights.
  • United Kingdom: MHRA announcements on gov.uk.
  • Trials: TRIUMPH records on ClinicalTrials.gov (for example NCT05929066).

Frequently asked questions

When will retatrutide be available in pharmacies?

No date can be given. The first Phase 3 results were published in 2026, and Lilly said on 29 September 2026 that it plans to file with the FDA in the first quarter of 2027. Approval and national licensing take further time. Check FDA, EMA and MHRA announcements for the current status.

Is retatrutide more effective than Mounjaro?

There is no answer yet. The TRIUMPH trials compared retatrutide with placebo; no published trial compares it head to head with tirzepatide (Mounjaro). Trials of different length and population cannot be compared by putting their numbers side by side.

Do Phase 3 results mean the drug is approved?

No. Phase 3 results form the basis of a marketing application, but the decision belongs to regulators such as the FDA, the EMA and the MHRA. As of October 2026 there is no approval anywhere.

Is it safe to take retatrutide right now?

No. The drug has not been approved and cannot be sold legally. Products sold online are unregulated and carry serious health risks.

Sources

Last reviewed: 15 October 2026