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Research use only
· 7 min read
"GLP-1 peptide" gets used as if it named one thing. In the research literature it names a receptor, and the compounds filed under it engage that receptor in very different company - some alone, some alongside one or two other receptors entirely. The useful way to read the class is not by what each molecule is marketed as but by which receptors it touches. This is a research-context guide to that map: what GLP-1 is, what its receptor is, and how mono-, dual- and triple-agonist pharmacology actually differs across the GIP, GLP-1 and glucagon receptors, with amylin handled separately as the receptor axis it really sits on. Everything below describes what published studies have characterised, not any human use; compounds are named only by receptor pharmacology and are supplied strictly as research reagents.
GLP-1 stands for glucagon-like peptide-1, an incretin hormone. The name carries its own lineage: it is cleaved from the same proglucagon precursor that yields glucagon, which is why the two are "glucagon-like" without being interchangeable. As an incretin, it belongs to the family of gut-derived peptides that the comprehensive review literature characterises as signalling molecules of nutrient-sensing physiology (Mueller et al., Molecular Metabolism, 2019). The point worth holding onto is that GLP-1 the hormone and GLP-1 the receptor are two different objects. The hormone is the natural ligand; the receptor is the lock it fits. When suppliers and search engines say "GLP-1 peptide", they almost always mean a synthetic molecule engineered to act at that receptor, not the endogenous hormone itself.
The GLP-1 receptor (GLP-1R) is a class B G-protein-coupled receptor. That classification is not trivia. Class B GPCRs share a large extracellular domain that captures the peptide ligand and a transmembrane bundle that transmits the signal inwards, and the incretin and glucagon receptors all belong to the same structural neighbourhood. GLP-1R, the glucose-dependent insulinotropic polypeptide receptor (GIPR) and the glucagon receptor (GCGR) are three close relatives within that class B family. Their structural similarity is exactly what makes a single engineered peptide able to engage more than one of them at once - the receptors are different enough to be selective targets but related enough that one molecule can be designed to fit several. The receptor-pharmacology literature treats these three as a connected set rather than three unrelated switches (Mueller et al., Molecular Metabolism, 2019).
The cleanest way to separate the compounds in this space is to count receptors, not to read labels. The published structural pharmacology supports a tidy ordering by how many of the class B receptors a molecule activates.
Mono-agonists act at a single receptor. A GLP-1 receptor mono-agonist engages GLP-1R and nothing else in this set. Semaglutide is the approved medicine most often named here for search relevance; in receptor-pharmacology terms it is described as a GLP-1R mono-agonist, and it is mentioned only as an informational reference point, never positioned by any indication.
Dual agonists add a second receptor. The most discussed combination pairs GIPR with GLP-1R from a single sequence. Tirzepatide is the approved medicine named here, again purely for relevance, and described in the literature as a dual GIP/GLP-1 receptor agonist with no glucagon-receptor arm. Naming it describes which receptors it engages, not any effect.
Triple agonists add the third class B receptor, glucagon. Retatrutide (developer code LY3437943) is the research compound at this end of the axis: a single engineered molecule characterised as engaging GIPR, GLP-1R and GCGR at once. Its discovery paper (Coskun et al., Cell Metabolism, 2022; the journal's own title uses promotional language not reproduced here) reports the in-vitro receptor binding and signalling assays that define it as a triple incretin and glucagon receptor agonist. A lineage detail that resists the "just a GLP-1 with extra receptors" shorthand: its backbone is borrowed from GIP, not GLP-1. PubChem indexes it under CID 171390338 with the molecular formula C221H342N46O68 and a molecular weight of approximately 4731 g/mol. The added glucagon-receptor activity is the single mechanistic feature most often cited to distinguish a triple agonist from a dual one - a receptor count, not a benefit.
Two molecules with the same receptor count are still distinct chemical entities with distinct backbones and side chains. The receptor map sorts the class; it does not make members of a tier interchangeable. The table below collapses the comparison to receptor targets and molecular class only - never efficacy.
| Compound | Receptors engaged | Molecular class |
|---|---|---|
| Semaglutide (reference only) | GLP-1 | GLP-1R mono-agonist peptide |
| Tirzepatide (reference only) | GIP + GLP-1 | Dual incretin receptor agonist peptide |
| Retatrutide (LY3437943) | GIP + GLP-1 + glucagon | Triple incretin/glucagon receptor agonist peptide |
| Cagrilintide | Amylin / calcitonin (not GLP-1) | Long-acting amylin analogue |
The reason semaglutide and tirzepatide appear as plain text and not as links is deliberate: they are approved medicines, named here only so the receptor map is legible, and Kovalabs supplies neither. The only stocked compounds on this page are research reagents.
Amylin analogues get swept into "GLP-1 peptide" conversations all the time, and on receptor grounds that is simply wrong. Cagrilintide is the example worth pinning down. It is an amylin analogue, and amylin does not act at GLP-1R, GIPR or GCGR at all. Its receptors are the amylin receptors, which the canonical pharmacology describes as complexes of the calcitonin receptor with receptor-activity-modifying proteins (Hay et al., British Journal of Pharmacology, 2018). A structural study later resolved how that complex defines the amylin phenotype (Cao et al., Science, 2022). In other words cagrilintide is on a different lock-and-key system entirely - it belongs in this discussion as a contrast axis, not as a member of the GLP-1 class. PubChem indexes cagrilintide under CID 171397054. Filing it next to the incretin agonists by receptor pharmacology would be a category error; it is included here precisely to mark the boundary of the GLP-1 receptor family.
The receptor map is far better established than anything downstream of it, so it is worth taking the levels separately. The receptor classifications themselves are settled: GLP-1R, GIPR and GCGR as class B GPCRs, amylin receptors as calcitonin-receptor complexes, and the molecular identities of the named compounds (retatrutide CID 171390338, formula C221H342N46O68; cagrilintide CID 171397054) are settled chemistry and pharmacology, backed by binding assays and resolved structures. The mechanistic middle ground is in-vitro potency assays and animal-model studies of how mono-, dual- and triple-agonism behave at the receptor, but a clean receptor count does not translate into a clean prediction about anything in a living body. The weakest level is what those receptor profiles produce in humans: the subject of trials whose endpoints are study design, not findings a reader should infer from a blog. These are investigational compounds, not licensed medicines, and they have not been shown to produce defined outcomes in humans. Read the receptor pharmacology as settled and the human outcomes as still open.
The compounds discussed here are supplied by Kovalabs for laboratory and in-vitro research only. They are not medicines, not supplements, and not for human or veterinary use, and nothing on this page describes a dose, a route, a schedule or an outcome. Semaglutide and tirzepatide are named only as informational reference points and are not products. Retatrutide and cagrilintide are investigational compounds that have not been evaluated by the MHRA or any comparable regulator for safety or efficacy in humans or animals. Every batch is third-party tested with a certificate of analysis. See the full research disclaimer for terms.
In research usage, "GLP-1 peptide" refers to a synthetic molecule engineered to act at the GLP-1 receptor, a class B G-protein-coupled receptor. The endogenous hormone glucagon-like peptide-1 is the natural ligand for that receptor; the compounds discussed under the term are engineered ligands grouped by which receptors they engage.
The difference is how many of the class B receptors a single molecule activates. A mono-agonist engages one (GLP-1R), a dual agonist engages two (commonly GIPR plus GLP-1R), and a triple agonist engages three (GIPR, GLP-1R and GCGR). It is a receptor count, not a statement about effect. See retatrutide vs tirzepatide by receptor pharmacology for the dual-versus-triple contrast.
No. Cagrilintide is an amylin analogue acting at the amylin receptors, which the literature describes as calcitonin-receptor complexes. It does not act at GLP-1R, GIPR or GCGR, so by receptor pharmacology it sits on a separate axis from the incretin agonists and is included here only as a contrast.
No. Semaglutide and tirzepatide are approved medicines, named on this page only as informational reference points for the receptor classes. They are not products and are not supplied by Kovalabs.
Retatrutide (developer code LY3437943) is indexed in PubChem under CID 171390338 with the molecular formula C221H342N46O68 and a molecular weight of about 4731 g/mol. Cagrilintide is indexed under CID 171397054. See the retatrutide as a triple-agonist research peptide monograph for the full chemistry breakdown.