What retatrutide is
Retatrutide, development code LY3437943, is a synthetic peptide engineered to activate three metabolic receptors from a single molecule: the glucagon-like peptide-1 receptor (GLP-1R), the glucose-dependent insulinotropic polypeptide receptor (GIPR), and the glucagon receptor (GCGR).
It represents the third step in a clear line of development. Single GLP-1 agonists came first, dual GLP-1/GIP agonists followed, and retatrutide adds glucagon receptor activity to the same backbone strategy. Each step has been an attempt to recruit more of the endogenous incretin and glucoregulatory system from one injectable molecule rather than combining agents.
Molecular profile
| Property | Value |
|---|---|
| Development code | LY3437943 |
| CAS number | 2381089-83-2 |
| Receptor targets | GLP-1R, GIPR, GCGR |
| Molecular weight | ~4,731 Da |
| Modification | C20 fatty-diacid conjugation |
| Circulating half-life | ~6 days (albumin binding via the fatty acid) |
| Appearance | White to off-white lyophilised powder |
Why the third receptor matters
GLP-1 receptor activity drives the insulinotropic and satiety-associated effects that made the first generation of these compounds interesting. GIP receptor activity appears to complement it, with published dual-agonist data showing greater effect than GLP-1 activity alone.
The glucagon receptor is the counterintuitive addition. Glucagon opposes insulin and raises hepatic glucose output, which reads as the wrong direction for a metabolic agent. The rationale is that glucagon receptor activation also increases energy expenditure and promotes hepatic lipid oxidation, and that when it is combined with sufficient GLP-1 and GIP activity, the glucose-raising component is offset while the energy-expenditure and liver-fat effects remain. Whether that balance holds across models is precisely what the compound is studied to establish.
Research context
Phase 2 clinical data published in 2023 reported dose-dependent reductions in body weight over 48 weeks, alongside improvements in glycaemic markers in participants with type 2 diabetes and reductions in liver-fat fraction. In preclinical and in-vitro work, retatrutide is used to probe the pharmacology of combined incretin and glucagon signalling — receptor binding and selectivity assays, cAMP accumulation as a functional readout of receptor activation, and comparative work against single and dual agonists.
Tested Peptides supplies retatrutide as a chemical reference material for in-vitro laboratory research. Nothing on this page is a therapeutic claim, and no dosing or administration guidance is provided.
Analytical notes
Retatrutide is a large, fatty-acid-conjugated peptide, and both properties bear on how it is characterised.
Purity by HPLC. Reversed-phase separation of a lipidated peptide of this size tends to produce a broader main peak than an unmodified short peptide, and the impurity profile of interest sits close to the main peak — deletion sequences missing a single residue, and species where the fatty-acid conjugation is incomplete or has occurred at the wrong position. A purity figure quoted without the chromatogram behind it hides exactly that detail.
Identity by mass spectrometry. Confirming observed mass against theoretical mass is what distinguishes correctly assembled retatrutide from a related incretin analogue. The compounds in this class share substantial sequence homology, and chromatography alone will not reliably separate the question of "how pure" from the question of "pure what".
Net peptide content. Like most synthetic peptides, retatrutide is supplied as a salt with residual water, so gross vial mass exceeds peptide mass. Where molar precision matters, work from the net peptide content on the Certificate of Analysis rather than the label figure — see net peptide content versus purity.
Handling and storage
Store the sealed vial at −20 °C, protected from light and moisture. Allow it to reach room temperature before opening, so that atmospheric moisture does not condense onto cold lyophilised cake.
Fatty-acid-conjugated peptides are unusually susceptible to interfacial aggregation. Add diluent slowly down the inside wall of the vial rather than directly onto the cake, and swirl gently — never shake or vortex. Store reconstituted solution at 2–8 °C, protected from light, and avoid repeated freeze-thaw cycles.
What we supply
Retatrutide is released against a ≥99% purity specification, with in-house HPLC and mass spectrometry on every batch and a batch-specific Certificate of Analysis carrying the batch number printed on the vial. Select batches additionally receive independent purity verification by a third-party laboratory. Ordering opens at launch; nothing is released before the analysis is in hand.