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Retatrutide vs Tirzepatide
Both are incretin-based metabolic research compounds. Tirzepatide targets dual incretin pathways (GIP and GLP-1). Retatrutide adds a third receptor arm, glucagon, making it a triple agonist with stronger metabolic-marker signals in the published Phase 2 literature.
Retatrutide
GLP-3(RT) (LY3437943) is a synthetic unimolecular triple agonist: a single molecule that switches on three receptors at once. Those receptors are the glucagon-like peptide-1 receptor (GLP-1R), the glucose-dependent insulinotropic polypeptide receptor (GIPR), and the glucagon receptor (GcgR). GLP-1R agonism suppresses appetite via hypothalamic satiety signaling, slows gastric emptying (how quickly the stomach empties), and potentiates glucose-stimulated insulin secretion. GIPR agonism augments incretin-mediated insulin release. It may also directly potentiate the appetite-suppressing (anorectic) effects of GLP-1 through central and peripheral synergy. The third arm, glucagon receptor agonism, is what distinguishes GLP-3(RT) from dual GLP-1/GIP agents. GcgR activation increases hepatic glucose output, elevates resting energy expenditure via brown adipose tissue thermogenesis (heat production in brown fat), promotes hepatic lipid oxidation, and suppresses appetite through independent CNS circuits. Preclinical data in diet-induced obese rodents showed that the triple agonist combination produced substantially greater weight reduction than any dual-agonist pair, which suggests the three arms contribute in non-redundant ways. The compound is currently in Phase 3 (TRIUMPH program) following its Phase 2 results.
Tirzepatide
Tirzepatide (LY3298176) is a synthetic dual agonist peptide that activates both the glucagon-like peptide-1 receptor (GLP-1R) and the glucose-dependent insulinotropic polypeptide receptor (GIPR). Structurally, it is a 39-amino acid peptide based on the native GIP sequence, with modifications that let it also activate GLP-1R. A C18 fatty diacid chain is attached through a linker so the peptide binds albumin, the most abundant blood protein. That binding extends plasma half-life to approximately 5 days and allows once-weekly dosing. GLP-1R agonism reduces appetite through hypothalamic and brainstem satiety pathways, slows gastric emptying, and augments glucose-stimulated insulin release from pancreatic beta cells while suppressing glucagon. GIPR agonism complements this by further potentiating insulin secretion in a glucose-dependent manner. It may also modulate adipocyte lipid metabolism, reduce glucagon secretion, and enhance the appetite-suppressing (anorectic) effects of GLP-1R signaling through central GIPR circuits in the hypothalamus and area postrema. Tirzepatide received FDA approval for type 2 diabetes (Mounjaro, May 2022) and obesity (Zepbound, November 2023), making it the first approved dual GLP-1/GIP agonist.
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