GLP-3 (RT): What It Is and What It Does

What GLP-3 (RT) is

Retatrutide (research code LY3437943, nicknamed 'GLP-3') is a newer lab-made compound being tested in human clinical trials for metabolism. Here it is supplied as an analytical-grade reference material for laboratory research only.

Where it comes from

Retatrutide carries the research code LY3437943 and the informal nickname 'GLP-3.' It was developed by Eli Lilly as the next step in a line of incretin-mimicking compounds — molecules that copy the gut hormones released after eating. What made it distinctive is that a single engineered peptide was designed to switch on three receptors at once — GLP-1, GIP, and glucagon — rather than one or two. It entered human clinical trials in the early 2020s and quickly became one of the most closely watched molecules in metabolic science because of the size of the body-weight changes reported.

What it does — in plain terms

After you eat, your gut releases hormones that tell your brain 'I'm full' and help your body handle sugar and fat. Most metabolism drugs copy one of those signals — retatrutide is unusual because it copies three at once (GLP-1, GIP, and glucagon). In its human trials, that triple action produced some of the largest body-weight reductions researchers have recorded for this class of compound, which is why it's one of the most closely watched molecules in metabolic science.

How it works

The simplest way to picture retatrutide is as one molecule pressing three different metabolic buttons at the same time. Two of those buttons — the GLP-1 and GIP receptors — respond to 'incretin' hormones the gut releases after a meal. The third — the glucagon receptor — is unusual for this class, and it is the main thing that sets retatrutide apart from single- or dual-agonist compounds.

Through the GLP-1 arm, retatrutide appears to do what other GLP-1 mimics do in research: signal fullness to appetite centers in the brain, slow the rate at which the stomach empties, and prompt the pancreas to release insulin in a glucose-dependent way. The GIP arm adds a second incretin signal that also influences insulin handling and how fat tissue is managed.

The glucagon arm is the distinctive piece. Glucagon is often thought of only as the hormone that raises blood sugar, but it also increases energy expenditure and acts on the liver's handling of fat. Researchers hypothesize that adding controlled glucagon-receptor activity is why retatrutide's trials reported such large body-weight changes and notable reductions in liver fat — though tuning that third signal carefully is part of what makes the molecule complex to study.

What the research shows

Retatrutide stands out from most research peptides because its evidence base is built on human clinical trials rather than animal or cell work — though it is worth being clear-eyed that these are mostly Phase 2 studies, that the larger Phase 3 program is still ongoing, and that the compound is investigational and not an approved medicine. With that context, here is what some of the key published work actually reports.

• The New England Journal of Medicine, 2023 — reported large body-weight reductions over 48 weeks in a Phase 2 trial of adults with obesity, among the biggest recorded for this class of compound.
• Biomolecules, 2025 — reviewed retatrutide's triple-hormone mechanism and its emerging place in obesity pharmacotherapy research.
• European Journal of Pharmacology, 2024 — surveyed retatrutide's pharmacology and its dual role across obesity and diabetes research.
• The Lancet, 2023 — reported improved long-term blood-glucose (HbA1c) control alongside body-weight change in a Phase 2 trial in type 2 diabetes.
• Nature Medicine, 2024 — reported marked reductions in liver-fat content in a Phase 2a trial in participants with metabolic fatty-liver disease.
• Baylor University Medical Center Proceedings, 2025 — pooled trial data in a systematic review and meta-analysis of retatrutide's effect on body weight in obesity.
• Metabolism Open, 2024 — combined trial results in a meta-analysis of retatrutide's effects on body weight and metabolic markers.
• Diabetes, Obesity & Metabolism, 2026 — described the design and rationale of the Phase 3 TRIUMPH clinical-trial program evaluating retatrutide.
• The Lancet Diabetes & Endocrinology, 2025 — examined changes in body composition, including fat and lean mass, in a Phase 2 trial in type 2 diabetes.
• Journal of Basic and Clinical Physiology and Pharmacology, 2025 — reviewed the clinical-trial evidence on retatrutide in obesity research.

What GLP-3 (RT) is studied for

Body-weight change in obesity trials. This is retatrutide's most-watched research area. In Phase 2 trials in adults with obesity it produced some of the largest body-weight reductions recorded for this class, which is why the ongoing Phase 3 program is followed so closely.

Blood-sugar and insulin handling. In a separate Phase 2 trial in type 2 diabetes, researchers reported improved long-term glucose control (HbA1c) alongside metabolic benefits, reflecting the GLP-1 and GIP arms of its mechanism.

Metabolic fatty-liver disease. A Phase 2a study examined retatrutide in metabolic fatty-liver disease and reported substantial reductions in liver fat, an effect researchers link partly to its glucagon-receptor activity.

The triple-agonist mechanism. Beyond outcomes, retatrutide is studied as a tool for understanding what adding a third hormone signal (glucagon) to the usual GLP-1/GIP combination does to whole-body metabolism.

Storage & handling

As a lyophilized (freeze-dried) powder, retatrutide reference material is most stable kept cold and dark — refrigerated for short holds, or frozen for longer storage. Once reconstituted with bacteriostatic water it should be refrigerated at roughly 2-8 °C, kept out of light, and protected from repeated freeze-thaw cycles, which degrade peptides. See the reconstitution reference below for the concentration math.

Reconstitution reference

Standard laboratory reconstitution volumes for GLP-3 (RT), from the VNG Reconstitution Sheet. See the full reconstitution guide for the method and concentration math.