Retatrutide at a glance
Retatrutide is a synthetic peptide that appears in trial publications under the development code LY3437943. It belongs to the incretin class, next to semaglutide and tirzepatide, but reaches one receptor further than either: one chain with agonist activity at the GIP, GLP-1 and glucagon receptors. It is also the least mature of the three. No regulator has assessed it, and the phase 3 programme, TRIUMPH, is still running.
- Class: triple incretin agonist, with GIPR, GLP-1R and GcgR activity in one molecule.
- Half-life: roughly six days.
- Human evidence: a single randomised phase 2 obesity trial, published in 2023.
- Status: investigational, with no marketing authorisation in the EU or elsewhere.
How retatrutide works
Two of the three targets are familiar. GLP-1 receptor activation lowers appetite and slows gastric emptying; GIP receptor co-agonism, the addition tirzepatide introduced, supports insulin secretion. The third target is the odd one. Glucagon is the signal of the fasted state: it prompts the liver to release glucose, so a glucagon agonist would be expected to raise blood sugar.
The case for including it rests on what else glucagon does. It raises resting energy expenditure and steps up fat oxidation in the liver, so the receptor is also studied as a route to lowering liver fat. The GLP-1 component is expected to restrain glucagon-driven glucose output and keep insulin responsive. The three activities are not equal in strength: the glucagon arm was deliberately kept modest.
Oxyntomodulin, a gut peptide secreted after a meal, is the natural precedent. It stimulates both the GLP-1 and the glucagon receptor, so food intake falls while energy expenditure rises. Retatrutide is a long-acting, engineered version of that pairing with GIP activity added. A fatty acid chain binds it to albumin, which gives a half-life of about six days; Research Peptides Explained covers that technique.
The evidence ladder for retatrutide
| Evidence level | Model or trial | Main finding |
|---|---|---|
| Animal and human physiology studies | Glucagon receptor agonism in general | Higher energy expenditure and more fat oxidation in the liver |
| Randomised trial, phase 2 | Adults with obesity; four weekly doses compared with placebo; published 2023 | Mean weight change of −17.5% after 24 weeks on 12 mg; −24.2% after 48 weeks, where placebo gave −2.1% |
| Randomised trials, phase 3 | TRIUMPH programme | Running; nothing reported so far |
The ladder is short. Its one completed human rung is a phase 2 trial, a design meant to pick a dose and surface signals, not to establish a benefit. The study was smaller and shorter than SURMOUNT-1 for tirzepatide or STEP 1 for semaglutide, and it measured body weight, not illness or survival. The 48-week figure is the largest published for this class, but weight was still falling when the trial ended, so where the curve settles is unknown.
Above that rung there is nothing yet: no cardiovascular outcome trial, no randomised comparison with tirzepatide or semaglutide, no long-term safety record, no licensed use. Trials in fatty liver disease are part of the programme. No published human trial separates the three components, so the glucagon arm’s share of the weight effect is unknown. Semaglutide, Tirzepatide and Retatrutide Compared explains why figures from separate trials cannot simply be set side by side.
Retatrutide doses reported in studies
The values below are reference points from the one published trial. They describe a supervised study protocol and are not guidance; for a compound still in development, no human dose has been validated.
| Setting | Dose | Schedule | Route | Note |
|---|---|---|---|---|
| Phase 2 trial in obesity, published 2023 | 1, 4, 8 or 12 mg | Once weekly for 48 weeks | Subcutaneous | Compared with placebo |
| Escalation inside that trial | Low starting dose, raised in steps | A step every few weeks until the assigned dose | Subcutaneous | Under medical supervision |
| Licensed product | None | – | – | No approved label exists |
Semaglutide and tirzepatide have schedules that a regulator has examined; retatrutide has only a trial design. In it, participants moved up to their assigned dose slowly, because gut-related adverse events depend on how fast the dose rises as well as on how high it goes.
Safety findings and open questions
Safety knowledge comes from a few hundred trial participants followed for months, so read it as preliminary. The most frequent adverse events in the phase 2 trial were gastrointestinal: nausea, vomiting, diarrhoea and constipation. They rose with dose and clustered in the escalation period.
What sets retatrutide apart from the single and dual agonists is a rise in heart rate, with glucagon receptor activity as the suspected cause. The glucagon component did not undermine glycaemic control, although that balance was tested only within the dose range studied.
- Does the heart-rate increase matter over years? Phase 3 is expected to address this.
- What does long exposure do to the liver, the pancreas and the thyroid?
- How do older or frailer people respond?
- Which rare adverse events exist? A trial of this size cannot detect them.
Bench notes: storing and reconstituting retatrutide
Research-grade retatrutide is supplied as lyophilised powder in a sealed vial. The storage condition given for the powder is −20 °C, dry and dark.
Before opening, let the closed vial reach room temperature so that no condensation forms on the powder. Bacteriostatic water is the usual solvent for a stock solution that will be sampled more than once; King Peptides lists it as Bacteriostatic Water 10 ml. Run the solvent down the glass wall and swirl gently; do not shake. Keep the solution refrigerated and away from light. The sources give no stability figures for retatrutide in solution. The full procedure is in Storage and Reconstitution: A Bench Protocol.
Status in the Netherlands, Belgium and Luxembourg
No medicine containing retatrutide is authorised in the European Union or anywhere else. EU marketing authorisations run through the European Medicines Agency and apply in the Netherlands, Belgium and Luxembourg alike, so the position is the same in all three: no assessed dossier, no brand name, no pharmacy supply. Human exposure takes place lawfully only inside approved clinical trials.
Semaglutide and tirzepatide each exist as a licensed medicine and as a research chemical. Retatrutide has only the second identity: a vial offered for sale is an unapproved substance for laboratory work. National and institutional rules on possession and import differ, so check the ones that apply to you.
In sport, the WADA Prohibited List does not name retatrutide at present. The list is reissued every year, so athletes should consult the version in force.
Ordering retatrutide for research in the Benelux
King Peptides lists the compound as GLP-3 RT (Retatrutide) 10 mg. “GLP-3” is a trade label, not a scientific term: no hormone of that name exists. The chemical name and the lot number are what count.
No licensed retatrutide exists as a reference, so identification rests on paperwork. Every lot has a lot-specific certificate of analysis with HPLC and mass spectrometry, and the shop’s lab reports page lists HPLC purity at 99% or higher for most products, this one included. Check that the lot number matches your vial and that the mass reads 4731.3 Da, as in the panel on this page. Tirzepatide lies fewer than 100 Da away, so a coarse reading will not separate the two. The certificate of analysis guide covers each entry.
Orders are dispatched from the Netherlands in a tracked parcel: usually 1–2 business days within the Netherlands and 3–5 business days to other EU countries, Belgium and Luxembourg included, with no customs clearance inside the EU. The supplier checklist is in the Benelux buying guide.
Retatrutide: quick answers
What does LY3437943 refer to? The development code used for retatrutide in trial publications. Code and name describe the same molecule.
Can a pharmacy in the Benelux supply retatrutide? No. No authorised product exists, so there is nothing to dispense. Outside clinical trials it is available only as research material.
How firm is the 24.2% figure? It is the mean weight reduction at 48 weeks on 12 mg in one phase 2 trial, with 2.1% on placebo. Weight had not levelled off, and no second trial has confirmed it yet.
Has retatrutide been tested head to head with tirzepatide? No. The only direct comparison among the three incretin peptides is SURMOUNT-5, which set tirzepatide against semaglutide.
Research use only. This page describes Retatrutide for laboratory and scientific research. Research material has no marketing authorisation, whatever the status of the molecule as a medicine elsewhere, and is not meant for human or veterinary use. Nothing on this page is medical advice; the doses above are those reported in published studies, not recommendations. Check the rules that apply in your country and at your institution before ordering.