Research material and lot documents.
GLP-3 is an informal name for triple hormone receptor agonists such as retatrutide, and Eli Lilly's page of September 29, 2026 calls the term “a scientifically inaccurate label used informally in the media to describe triple hormone receptor agonists.” Source: Lilly, What to know about retatrutide.
Lilly's answer continues: This nickname emerged because the medication simultaneously targets three receptors, GLP-1, GIP and glucagon, rather than representing an actual scientific classification. The company also writes: A more suitable term to describe retatrutide is “triple agonist,” which accurately reflects the mechanism of action.
The GIP receptor, for glucose-dependent insulinotropic polypeptide.
The GLP-1 receptor, for glucagon-like peptide-1.
The glucagon receptor.
The abstract of the TRIUMPH-1 paper describes retatrutide as "a triple-receptor agonist of glucose-dependent insulinotropic polypeptide, glucagon-like peptide-1, and glucagon receptors." Source: 2026 New England Journal of Medicine, PMID 42814954. The retatrutide page summarizes what the 2022 Cell Metabolism paper reported about the receptors in cell assays and mice.
FDA's announcement of November 8, 2023 says Zepbound (tirzepatide) activates two hormone receptors, GLP-1 and GIP. Retatrutide adds the glucagon receptor. Source: FDA announcement, November 8, 2023. The retatrutide vs tirzepatide page compares the two molecules' trial records.
Because the label is informal, a listing called GLP-3 or RTA-GLP3 needs the substance behind it identified by name and mass. FDA's record lists retatrutide under UNII NOP2Y096GV, and PubChem lists a computed molecular weight of 4731 g/mol for CID 171390338. Sources: FDA UNII record for retatrutide and PubChem record, CID 171390338. One supplier's lot reports list retatrutide material as RTA-GLP3 (RETA) in Curo's lot-certificate library.