Retatrutide is not a "GLP-3" in any biological sense, because no GLP-3 hormone or receptor exists; it is a synthetic 39-residue peptide that acts as an agonist at the GLP-1, GIP and glucagon receptors in vitro. "GLP-3" is a catalog nickname for it, which is why the same compound appears as GLP-3 RT, GLP3RT and RT-GLP3.
This short guide answers the naming question directly for researchers who run into "is retatrutide a GLP-3?" or "is reta a GLP-3?" and want a clean, lab-oriented answer.
Is retatrutide a GLP-3?
As a label, yes: suppliers who number their incretin-type catalog items GLP-1, GLP-2, GLP-3 put retatrutide in the third slot. As a classification, no: "GLP-3" is not a defined peptide family or receptor class. The broader nomenclature background, including the real proglucagon-derived peptides, is in Is There Such a Thing as GLP-3?. The full naming and identity profile is in the hub guide listed below.
Why does the "GLP-3" nickname exist?
Retatrutide extends the receptor logic of earlier engineered incretin-type peptides by adding a third target. A numbered ladder (one receptor, two receptors, three receptors) is an easy way for a catalog to group them, and the "GLP-3" name stuck because it is short and searchable. It describes the catalog position, not the pharmacology. The store lists the material as RT-GLP3 (retatrutide), CAS 2381089-83-2.
Is reta a peptide?
Yes. "Reta" is an informal short form of retatrutide, which is a peptide: a linear chain of 39 amino-acid residues with a C-terminal amide. It is a modified peptide, because it carries non-coded residues and a lysine side chain bearing a C20 fatty diacid through a linker. It is therefore a lipidated synthetic peptide, not a protein and not a small molecule.
How does the receptor profile compare with related research peptides?
Receptor coverage is what separates retatrutide from the single- and dual-receptor peptides it is often grouped with. The table lists in vitro receptor targets only.
| Compound | GLP-1R | GIPR | GCGR |
|---|---|---|---|
| Semaglutide | Agonist | No | No |
| Tirzepatide | Agonist | Agonist | No |
| Retatrutide ("GLP-3 RT") | Agonist | Agonist | Agonist |
Within the three-receptor profile, activity is not assumed to be equal at each receptor, so concentration-response curves are run separately per receptor. The assay framework is in the store's researcher's guide to retatrutide.
What should a researcher check instead of the name?
- CAS number 2381089-83-2 on the specification.
- Free-peptide formula C221H342N46O68 and a mass near 4731 g/mol.
- A batch report with HPLC purity and mass-spectrometry identity.
Related research guides
Research-use note
All materials discussed are supplied for in vitro laboratory research use only, and are not for human or animal use.
