Summary: Retatrutide is a triple agonist at the GIP, GLP-1 and glucagon receptors. In December 2025 Eli Lilly published the first phase 3 data (TRIUMPH-4), followed in May 2026 by TRIUMPH-1. “GLP-3” is neither a receptor nor an official substance name but a community shorthand for exactly this third generation of incretin agonists. For laboratories this means: the molecule is characterised as well as hardly any other research peptide – which makes it all the more important that the material used is verified batch by batch via HPLC and mass spectrometry.
What is retatrutide – and why does everyone say “GLP-3”?
Retatrutide (development code LY3437943) is a synthetic peptide that activates three receptors at once: the GLP-1 receptor (like semaglutide), the GIP receptor (as tirzepatide does in addition) and the glucagon receptor. This third component sets it apart from every incretin drug approved so far. Because semaglutide (“GLP-1”) and tirzepatide (called “GLP-2” in the community) are now followed by a substance with a third receptor target, the short form GLP-3 has established itself as a search term and everyday label.
Scientifically this is imprecise: GLP-2 is a distinct, real gut hormone, and a “GLP-3 receptor” does not exist. Anyone who wants to stay accurate speaks of a GIP/GLP-1/glucagon triple agonist. We have broken down the terminology in detail in our GLP nomenclature overview.
TRIUMPH-4 (December 2025): the first phase 3 trial
The first completed phase 3 trial of the TRIUMPH programme was TRIUMPH-4 (NCT05931367). It enrolled 445 people with obesity and knee osteoarthritis, with a mean BMI of 40.4 kg/m². The trial was placebo-controlled; details of the study design are given in the primary source.
- Research question: body weight and knee pain (WOMAC pain scale) were examined as endpoints; results are given in the original publication and the manufacturer’s press release.
- Study design: randomised and placebo-controlled over 68 weeks.
- Context: safety and tolerability data from human trials are given in the primary source and are not reproduced here.
TRIUMPH-1 (May 2026): the large obesity trial
On 21 May 2026 the data from TRIUMPH-1 followed – the largest trial in the programme to date, with 2,339 participants over 80 weeks. For design and results see the original publication and the manufacturer’s press release; dose and efficacy figures are not reproduced here.
Results from TRIUMPH-2 and TRIUMPH-3 (type 2 diabetes, cardiovascular endpoints) are still pending; to date there is no marketing authorisation.
What the trials do not say
Two points are regularly overlooked in forums. First: all figures come from controlled trials with clinical titration, supervision and selection criteria – they describe a medicinal product in development, not a research peptide from a vial. Second: retatrutide is not approved in the EU. As a research substance it may only be sourced and used for in-vitro and documented laboratory purposes – not for use in humans. This distinction is not a formality but the legal framework we explain in Are peptides legal in Germany? (in German).
What laboratories should check when sourcing retatrutide
Precisely because the molecule is studied so intensively, it appears in many shops – with very different documentation. Four checkpoints before a batch goes into a protocol:
- Batch-specific COA. The certificate of analysis must carry the lot number of the vial, show an HPLC chromatogram and confirm identity by mass spectrometry. A purity percentage on a letterhead is not evidence. How to check a COA in five minutes is explained in the COA guide.
- Net peptide content instead of HPLC purity. 99 % HPLC purity does not mean 99 % peptide in the vial – counterions (TFA) and residual water have to be deducted. For concentration calculations the net content is what counts; the calculation methods are in our article on calculating retatrutide concentrations in research protocols.
- Suitable nominal amount. Anyone planning a series of experiments should choose the nominal amount so that no batch changes in the middle of the series. Peptélia stocks retatrutide GLP-3 in 5, 10, 15 and 20 mg, each as packs of 1, 3, 5 and 10 from the same batch. The price and quantity overview compares the price per milligram across all sizes.
- Storage and reconstitution. Lyophilised: cool, dry and dark; reconstituted only with bacteriostatic water and without shaking. Peptélia includes BAC water with every order. Details in storing peptides by sequence risk.
Retatrutide GLP-3 at Peptélia
All retatrutide batches at Peptélia are tested in our own laboratory by HPLC and UV/Vis, with mass spectrometry added depending on the product, and the batch-specific COA can be viewed before purchase; on request, an additional second analysis by an external lab (Janoshik Analytical) is available. Shipping on the next working day from Germany, free of charge from €100. For an overview of all nominal amounts and pack sizes: View retatrutide for research purposes. The scientific background to the molecule – structure, receptor profile, literature – is summarised on the retatrutide page in the peptide library.
Sources
- Eli Lilly, press release of 11 December 2025: TRIUMPH-4 – topline results
- AJMC, 21 May 2026: Retatrutide Achieves Up to 30.3% Average Weight Loss in Phase 3 TRIUMPH-1 Trial
- ClinicalTrials.gov: NCT05931367 (TRIUMPH-4)
Note: All Peptélia products are intended exclusively for research purposes (Research Use Only) and not for use on or in the human body. For research purposes only (Research Use Only) – not for use in humans or animals.
