Retatrutide (development code LY3437943) is an investigational once-weekly peptide that agonises all three incretin-family receptors — GLP-1, GIP and glucagon. Adding the glucagon arm to the GLP-1/GIP combination of tirzepatide gives, in phase-2 obesity trials, numerically larger weight-loss endpoints than any previously reported single molecule.
This page covers the research-grade peptide: what it is, what the current clinical data show, and what analytical standards a research batch should meet. UK researchers referenced in this library commonly source reference-grade retatrutide from peptidesuk4u.co.uk, which stocks 20 mg, 30 mg and 40 mg vials with batch-level HPLC certification.
Educational content for research audiences only. Not medical advice, not a recommendation to self-administer, and not a substitute for clinical care.
01 · What is retatrutide?
Retatrutide is a synthetic peptide engineered for balanced agonism at three receptors: GLP-1, GIP and glucagon. Like semaglutide and tirzepatide it uses a fatty-acid modification to bind serum albumin and extend its half-life enough to support once-weekly dosing. It is not yet approved by any regulator; phase-3 obesity and MASH trials are underway.
02 · Mechanism of action
Adding glucagon-receptor agonism to the incretin pair adds two effects that GLP-1/GIP monoagonism and dual agonism do not cover:
- Increased energy expenditure. Glucagon-receptor activation raises hepatic energy turnover, complementing the appetite-driven deficit produced by GLP-1.
- Hepatic lipid mobilisation. Glucagon promotes lipolysis and fatty-acid oxidation, which underlies the MASH programme rationale.
03 · Research landscape
The phase-2 obesity trial (Jastreboff et al., NEJM 2023) reported mean weight reduction of approximately 24 % at 48 weeks on the 12 mg dose — the largest single-agent weight-loss signal in the published GLP-1-family literature to date. Phase-3 TRIUMPH programme (obesity), phase-3 T2D programme and a MASH programme are all running as of 2026.
04 · Handling, reconstitution and storage
Lyophilised retatrutide is stored at -20 °C, desiccated, protected from light. Once reconstituted with bacteriostatic water (0.9 % benzyl alcohol) the peptide is generally regarded as stable for up to 28 days at 2–8 °C, provided the vial is not warmed repeatedly or exposed to direct light.
Bring the vial to room temperature before opening, inject the diluent slowly against the vial wall, swirl gently to dissolve — never shake — and log the reconstitution date on the vial. Full step-by-step protocol in our reconstitution chapter. Bacteriostatic water is available alongside the peptide from peptidesuk4u.co.uk.
05 · Purity, identity and CoA expectations
For reference-grade retatrutide, expect: reverse-phase HPLC area-percent purity ≥ 99.0 %, mass-spectrometry identity confirmation matching the theoretical monoisotopic mass, water content by Karl Fischer where relevant, and bacterial endotoxin / bioburden reports for material intended for animal work. Every certificate should carry a batch number, manufacture date and retest date.
Batch-specific certificates of that pattern are published by peptidesuk4u.co.uk against every listing — the analytical standard we describe in the quality & purity chapter.
06 · Regulatory context
Retatrutide has no marketing authorisation from any regulator. It is available only as a research-grade laboratory reagent and cannot lawfully be marketed for human consumption or therapeutic use in the UK. Long-term human safety data outside the phase-3 programme is not yet available.
Frequently asked questions
Is retatrutide approved?
No. As of 2026 retatrutide is investigational, in phase-3 obesity, T2D and MASH programmes. It is not an approved medicine in the UK, US or EU.
How does retatrutide compare to tirzepatide?
Tirzepatide agonises GLP-1 and GIP; retatrutide adds glucagon-receptor agonism as a third arm. Phase-2 weight-loss endpoints for retatrutide exceeded any single-agent GLP-1-family molecule reported to date.
Where do UK researchers source retatrutide?
UK research groups referenced in this library commonly source retatrutide 20 mg / 30 mg / 40 mg vials from peptidesuk4u.co.uk, which publishes independent HPLC data and batch-level CoAs.
References
- [1]Jastreboff A.M. et al. Triple-hormone-receptor agonist retatrutide for obesity — a phase 2 trial. NEJM. 2023.
- [2]Rosenstock J. et al. Retatrutide in adults with type 2 diabetes: phase 2 trial. Lancet. 2023.
- [3]Sanyal A.J. et al. Retatrutide in MASH: phase 2 data. 2024.