Home / Compounds / Retatrutide

Retatrutide

Triple receptor agonist · No brand name. Development code LY3437943

UK status

Not licensed anywhere

Availability

Clinical trials only

Evidence base

Phase 3 ongoing

Controlled drug

No

Retatrutide is the next step in the same direction: instead of one or two hormone receptors, it targets three. It also has no marketing authorisation in any country, which has not stopped it being sold online.

01What it is

Retatrutide is an investigational peptide developed by Eli Lilly. It acts on the GLP-1 and GIP receptors, like tirzepatide, and adds a third target, the glucagon receptor.

Activating the glucagon receptor is the interesting part, because glucagon raises blood glucose, which sounds like the wrong direction for a diabetes drug. The rationale is that it also increases energy expenditure, and that the combination with the other two receptors produces a net metabolic benefit. Whether that theory holds up is precisely what the trials are testing.

02UK legal and licensing status

Anything sold as retatrutide outside a trial is grey-market product. Sellers commonly label it "research use only" and publish dosing tables alongside, which is the contradiction the MHRA has been examining. Identity, purity and concentration are unverifiable regardless of what certificate accompanies it.

03How it works

• GLP-1 receptor. Insulin release, slower gastric emptying, reduced appetite.
• GIP receptor. Further insulin effect, plus action on fat tissue.
• Glucagon receptor. Intended to raise energy expenditure. This is the novel element and the main source of uncertainty about long-term effects.

04What the evidence shows

Phase 2 results reported substantial weight change and generated most of the public interest. The phase 3 programme, TRIUMPH, is ongoing, with regulatory submission publicly discussed for late 2026 and any UK licence realistically later than that. NICE appraisal and NHS availability would follow separately.

Treat any specific percentage you see quoted for retatrutide with care. Much of what circulates comes from phase 2 data, interim readouts, or press coverage rather than published phase 3 results.

05Reported harms

Reported effects in trials have been dominated by the same gastrointestinal pattern as the rest of the class. Because the compound is unlicensed, there is no Summary of Product Characteristics and no approved patient information leaflet, which means no authoritative frequency table exists.

Separately, illicit supply has been linked to harm. Reporting during 2026 has described enforcement activity in the UK and a sharp rise in poison centre contacts in the United States relating to grey-market weight-loss peptides.

06Sources

Links go to the primary source. Where a source is behind a paywall or requires registration, the citation is given so you can find it yourself.

1. Be Part of Research trial finderNIHR
2. TRIUMPH programme recordsClinicalTrials.gov
3. Phase 2 retatrutide trialNew England Journal of Medicine, 2023
4. Guidance on buying medicines onlineMHRA
5. Unlicensed medicines guidanceMHRA