Weight & Metabolic
Retatrutide
aka LY3437943 · 'triple-G' agonist · reta · retta · triple g · triple agonist · glp-3 · rt glp3 · glp3 · ret
Grade
An experimental once-weekly injectable that hits three metabolic hormone receptors at once and has produced the largest trial weight-loss results seen so far. It is not yet an approved medicine.
- Class
- Synthetic triple receptor agonist peptide (GLP-1 / GIP / glucagon)
- Evidence
- Grade B · Promising human evidence
- Sport / WADA
- Prohibited at all times under S0 (non-approved substances). The WADA 2026 Prohibited List bans any substance not covered by another section that has no current approval by any government health authority for human therapeutic use, explicitly including drugs in clinical development. As of October 2026 retatrutide is not approved anywhere in the world; Eli Lilly plans to file for approval in early 2027.
- Last reviewed
- 2026-06
Grade B · Promising human evidence
Why this grade
A genuine investigational medicine with large, published, randomised human trials showing some of the biggest weight-loss figures recorded. It scores B rather than A only because it is still in Phase 3 and not yet approved. The human evidence is strong and growing, but not yet final.
What is it?
Why people buy it
People buy it to lose weight. It is a new weight-loss injection still being tested by a drug company.
What we actually know
- •It has been tested in large, proper studies in people.
- •In one study, people on the highest amount lost about 24% of their weight in under a year.
- •Bigger final studies are still running. It is not approved as a medicine anywhere yet.
- •In the UK you can only get it legally by joining an approved trial.
What might happen
- •Weight loss is likely. Feeling sick, being sick and diarrhoea are common.
- •Some people had a faster heartbeat for a while. This is still being looked at.
- •Nobody knows yet about long-term safety, muscle loss, or weight coming back after stopping.
- •Anything sold online as retatrutide is unregulated. Nobody checks what is really in the bottle.
Bottom line
A strong weight-loss drug in real trials, but not approved yet. Online vials are not the drug that was tested.
Know someone taking this?
Send on WhatsAppIf the current weight-loss injections are a car with one strong engine (GLP-1), retatrutide is a car with three engines wired together, and in testing it's gone noticeably further on the same journey. Unlike most peptides people discuss, this car has actually been driven on real roads with real drivers in proper trials. It just hasn't passed its final road-legality test yet.
How is it meant to work?
Retatrutide is a unified peptide that switches on three receptors at once. GLP-1 and GIP agonism reduce appetite and improve blood-sugar handling. Glucagon-receptor agonism is thought to increase energy expenditure and mobilise fat from the liver. The combination drives weight loss beyond what single- or dual-agonists achieve.
What's it studied for?
Research contexts. Not proven uses, and not recommendations.
Does the human evidence stack up?
Strong and published. The Phase 2 obesity trial in the New England Journal of Medicine reported up to ~24% body-weight reduction at 48 weeks (the highest seen for an anti-obesity agent at the time), with parallel diabetes and fatty-liver data. The Phase 3 TRIUMPH programme is in progress and will decide durability, cardiovascular safety and approval. This is real clinical-grade evidence, not extrapolation.
What could go wrong?
- !Not yet approved or licensed anywhere. It remains investigational, so safety conclusions are provisional until Phase 3 completes.
- !Dose-related gastrointestinal side effects (nausea, vomiting, diarrhoea) are common, as with the whole incretin class.
- !Transient increases in heart rate have been reported and are still being characterised.
- !Because it is unapproved, any 'retatrutide' sold online is grey-market, unregulated and of unverified identity and purity. This is a very different and much riskier proposition than a future licensed product.
- !Long-term outcomes, muscle-mass effects and weight regain after stopping are not yet established.
Is it legal in the UK?
Retatrutide is an investigational medicine with no MHRA marketing authorisation. It is not available on prescription or legally for sale in the UK. It can only be received as a participant in an approved clinical trial. Any product marketed to UK consumers as 'retatrutide' is unlicensed and unlawful to supply for human use. For contrast, related GLP-1 medicines such as semaglutide and tirzepatide are MHRA-approved and prescription-only.
Key trials
- NCT04881760· Phase 2· Completed / published
Phase 2 dose-finding study in obesity (Jastreboff 2023)
Basis for the headline ~24% weight-loss figure.
- TRIUMPH programme· Phase 3· Ongoing
Phase 3 obesity & related outcome trials
Will determine durability, safety and whether retatrutide is approved.
Sources
- 01Triple-Hormone-Receptor Agonist Retatrutide for Obesity — A Phase 2 Trial — Jastreboff AM et al., New England Journal of Medicine (2023)
The landmark Phase 2 obesity RCT reporting up to ~24% weight loss at 48 weeks.
- 02Retatrutide for type 2 diabetes: a randomised, double-blind, Phase 2 trial — Rosenstock J et al., The Lancet (2023)
Companion Phase 2 trial in type 2 diabetes.
Compare with
Before you trust a vial
Peptides are freeze-dried for a reason. If you have seen Retatrutide sold pre-mixed in a ready-to-use pen or syringe, here is why that is a red flag for potency, sterility and dosing.
Storage & stability →Stay posted
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