GLP Research Peptides — GLP-1, GLP-2 and GLP-3

If you arrived here searching for a GLP-3 peptide, the compound you are looking for is retatrutide. GLP3 is the informal name the research and clinical-nutrition press has settled on for it, and the section below explains where that name comes from and what it does and does not mean.

What is in this category

Semaglutide (GLP1) is a selective GLP-1 receptor agonist. Tirzepatide (GLP2) is a dual agonist at the GIP and GLP-1 receptors. Retatrutide (GLP3) is a triple agonist at the GIP, GLP-1 and glucagon receptors. Bacteriostatic water is stocked separately for reconstitution.

What GLP-1, GLP-2 and GLP-3 mean here

These labels denote successive generations of incretin receptor agonist, ordered by how many receptors each compound engages — one, two, then three. They are not references to distinct endogenous hormones, and this is a common point of confusion worth stating clearly.

In particular, GLP-2 in this catalogue means tirzepatide, a dual GIP/GLP-1 agonist. It does not mean the endogenous glucagon-like peptide-2 hormone, which is a separate intestinotrophic peptide acting at its own receptor and is not stocked here. Likewise GLP-3 means retatrutide. If your protocol calls for authentic GLP-2, this is not the compound you need.

Why retatrutide is called GLP-3

The name is a market convention rather than a biochemical one. Proglucagon processing yields glucagon, GLP-1, GLP-2, glicentin and oxyntomodulin — there is no endogenous peptide called GLP-3. The label was adopted because retatrutide is the third generation in a commercially recognisable sequence: one receptor, then two, then three. It has since been picked up widely enough that GLP3 retatrutide is now how a large share of readers refer to the compound, and we use it here for that reason rather than because it describes anything in the biology.

The distinction matters when you read the literature. Searching for GLP-3 in a journal database will return very little; searching for retatrutide, or for its development code LY3437943, will return the phase 2 programme and the receptor pharmacology work behind it.

Mechanism and evidence base

GLP-1 is an incretin hormone released from intestinal L-cells in response to nutrient intake. Signalling through the GLP-1 receptor, a class B G protein-coupled receptor, potentiates glucose-dependent insulin secretion, slows gastric emptying and acts on hypothalamic circuits involved in energy balance. Native GLP-1 has a plasma half-life of roughly two minutes owing to rapid DPP-4 cleavage; the analogues here carry structural modifications that resist that cleavage.

Adding receptors changes the pharmacology. GIP is the second incretin hormone, and co-agonism at GIP and GLP-1 receptors — the tirzepatide profile — produces effects that differ from GLP-1 agonism alone. Adding glucagon receptor agonism, as the GLP-3 peptide retatrutide does, introduces a further axis affecting hepatic glucose output and energy expenditure.

This class is unusual in the research-peptide catalogue in that all three compounds have published human clinical trial data rather than preclinical evidence only. Semaglutide and tirzepatide have been evaluated in large randomised phase 3 programmes; retatrutide has published phase 2 data. That distinction matters when reviewing literature — do not treat the evidence base for these compounds as equivalent to that of compounds characterised only in cell or animal models.

Reconstitution and stability

These compounds ship as lyophilised powder. Reconstitute with bacteriostatic water, introducing the solvent down the vial wall rather than directly onto the cake, and swirl rather than shake — peptides of this size are susceptible to shear-induced aggregation. Store lyophilised material at −20 °C and reconstituted solution at 2–8 °C. Our guide to storage and stability of GLP-1 peptides covers this in full, and the peptide reconstitution calculator handles the concentration maths.

Purity and COA verification

Every lot is analysed by an independent laboratory. Identity is confirmed by mass spectrometry against the expected molecular weight and purity by HPLC. Certificates are published on our COA and lab reports page, and our guide to reading a Certificate of Analysis explains how to interpret them.