Retatrutide (LY3437943) is a triple-action research peptide developed by Eli Lilly. Unlike semaglutide (a GLP-1 agonist) and tirzepatide (a dual GLP-1/GIP agonist), retatrutide acts on three receptors at once: GLP-1, GIP, and the glucagon receptor (GCGR). It is this third component that makes it unique — glucagon directly stimulates the breakdown of fat stores and raises the body’s energy expenditure.
Each of the three receptors makes its own contribution:
A phase 2 study (NEJM, 2023): participants on the maximum dose of retatrutide lost an average of 24.2% of body weight over 48 weeks — the highest figure among all incretins studied. For comparison: semaglutide shows ~15%, tirzepatide ~22%.
Semaglutide was revolutionary, but it has an efficacy ceiling — it works through a single receptor only. Tirzepatide added a second receptor and improved the result. Retatrutide took the next step by adding the glucagon component.
In practice this means:
Retatrutide is injected subcutaneously once a week. The lyophilized powder is reconstituted with bacteriostatic water. Storage is at 2–8°C. Once reconstituted, the solution is stable for up to 28 days when refrigerated.
A typical titration schedule:
Important: retatrutide is a research peptide intended for scientific purposes only (Research Use Only). All dosing information is based on clinical-trial data and is for reference only.
According to clinical trials, the most common side effects are gastrointestinal:
Most side effects occur at the start of use and when increasing the dose. Slow titration helps minimize discomfort.
A peptide’s quality is defined by its purity. Reputable manufacturers provide a Certificate of Analysis (CoA) with HPLC chromatography data. The purity of research-grade retatrutide should be at least 98%. Pay attention to shipping conditions — peptides are temperature-sensitive, and delivery without a cold pack can degrade the molecule.
Do not buy peptides from sellers who don’t provide a CoA or don’t maintain the cold chain in delivery. Saving on quality costs more in the end.
Obesity is a global problem, and incretin drugs have become one of the major breakthroughs of the last decade. Retatrutide is in phase 3 clinical trials, and interim results suggest it may become the most effective agent in its class. The triple mechanism delivers not only appetite suppression but active fat burning — the thing previous generations lacked.
For researchers and specialists working in metabolism, retatrutide is of particular interest as a tool for studying the interaction of incretin and glucagon pathways in the regulation of body weight.