Retatrutide (developmental code LY3437943) is a 39-amino-acid synthetic peptide engineered as a single-molecule agonist at the glucose-dependent insulinotropic polypeptide receptor, the glucagon-like peptide-1 receptor and the glucagon receptor. Its backbone carries 2-aminoisobutyric acid at positions 2 and 20, an alpha-methylated leucine at position 13 and a C-terminal serinamide; the lysine at position 17 is acylated on its epsilon-amine with an AEEA spacer, a gamma-glutamate and a C20 fatty diacid, which is the albumin-binding element.

It has been evaluated in phase 1 and phase 2 studies and is in the phase 3 TRIUMPH programme run by Eli Lilly, of which TRIUMPH-1 and TRIUMPH-3 reached primary completion in April 2026. As of August 2026 no new drug application has been filed with the FDA and retatrutide is not approved for marketing in any jurisdiction. It remains an investigational compound and cannot lawfully be prescribed or compounded outside a clinical study.

Because the molecule is still investigational there is no public reference standard against which a supplier's material can be independently checked in the way an approved drug can be. Identity in research-grade retatrutide therefore rests entirely on the supplier's own mass-spectrometry and HPLC data, and closely related analogues differing by one or two residues are not reliably distinguished by an HPLC purity figure alone.