Retatrutide Dr
Research digest · LY3437943

Retatrutide is the triple-receptor agonist that outpaced every approved obesity drug in Phase 3 trials — here is what the research actually measured.

Plain-English summaries of Phase 1, Phase 2, and Phase 3 data — mechanism, dose-response, adverse events, and the open questions the TRIUMPH program has not yet answered. Every quantitative claim is cited.

Read the research Jump to the numbers
Flat illustration of a single peptide chain connecting to three rounded receptor discs, one highlighted in warm orange
28.3% Mean weight reduction, Phase 3 TRIUMPH-1, 12 mg at 80 weeks
24.2% Phase 2 result at 12 mg, 48 weeks — no plateau observed
3 Receptors engaged simultaneously: GIP, GLP-1, glucagon
82.4% Liver fat reduction in the Phase 2a MASLD trial, 12 mg at 24 weeks

What Is Retatrutide?

Retatrutide (LY3437943) is an investigational synthetic peptide engineered to activate three gut hormone receptors simultaneously: the glucose-dependent insulinotropic polypeptide receptor (GIPR), the glucagon-like peptide-1 receptor (GLP-1R), and the glucagon receptor (GCGR).[6] That triple co-agonism is what distinguishes it from earlier compounds in the same class — dual GIP/GLP-1 agonists activate only two of those three targets.

Retatrutide is a 39-amino acid peptide conjugated to a C20 fatty diacid moiety via a lysine-17 linker. That conjugation enables albumin binding in plasma, extending the circulating half-life to approximately 6 days and supporting once-weekly subcutaneous dosing.[5][14] It is not a natural hormone — the receptors it targets are activated by natural gut peptides, but Retatrutide itself is a designed molecule.[14]

Developed by Eli Lilly and Company (internally designated LY3437943), Retatrutide is the subject of the TRIUMPH Phase 3 clinical trial program. As of mid-2026, it carries no approved indication in the United States, the European Union, or any other jurisdiction. It is accessible only through registered clinical trials.[21]

The TRIUMPH-1 pivotal trial results, reported in May 2026, documented a mean body weight reduction of 28.3% at 80 weeks in participants at the 12 mg dose — the largest mean weight reduction in the published obesity pharmacotherapy literature to date.[9]

Regulatory status

Retatrutide is investigational. No approved indication exists as of mid-2026. All dosage figures on this site refer to clinical research protocols, not prescribing guidance.

What Does Retatrutide Do?

Retatrutide activates three receptor pathways that together suppress appetite, slow gastric emptying, potentiate insulin secretion, and raise energy expenditure.[6] GLP-1 receptor activation reduces caloric intake and delays gastric emptying — effects established across the GLP-1 drug class. GIP receptor activation augments glucose-stimulated insulin secretion and modulates adipocyte lipolysis signaling. Glucagon receptor activation is the element distinct to the triple-agonist class: GCGR stimulation promotes hepatic fat oxidation and activates brown adipose tissue thermogenesis, producing energy expenditure increases that dual GIP/GLP-1 agonists do not deliver.[12]

In the Phase 2 obesity trial, participants receiving retatrutide at 12 mg once weekly achieved a mean body weight reduction of 24.2% at 48 weeks (versus 2.1% with placebo), with 83% reaching at least 15% weight loss.[1] The Phase 3 TRIUMPH-1 trial, in a population of 2,339 participants followed for 80 weeks, produced a mean reduction of 28.3% at 12 mg — and 45.3% of participants in that arm achieved at least 30% body weight loss.[9]

The Phase 2 type 2 diabetes trial documented up to 16.9% weight reduction and HbA1c improvements of up to 2.02% at 36 weeks at the highest doses, with 82% of high-dose participants reaching HbA1c ≤6.5%.[4] Retatrutide has also been studied in metabolic dysfunction-associated steatotic liver disease (MASLD): a Phase 2a trial recorded an 82.4% reduction in liver fat at 24 weeks at the 12 mg dose.[7]

What Is Retatrutide Used For?

The primary indication under investigation is obesity — specifically, adults with a BMI of 30 or higher, or a BMI of 27 or higher with at least one weight-related comorbidity. Secondary indications under active study include type 2 diabetes, metabolic dysfunction-associated steatotic liver disease (MASLD/MASH), and cardiovascular outcomes in participants with established cardiovascular disease.[21]

The TRIUMPH Phase 3 program comprises multiple concurrent trials. TRIUMPH-1 is the pivotal obesity efficacy trial (n=2,339, 80 weeks).[9] TRIUMPH-4 studied participants with obesity and knee osteoarthritis (68 weeks) and documented a 28.7% mean body weight reduction alongside a 75.8% reduction in WOMAC knee pain scores at 12 mg.[10] TRIUMPH-3 (NCT05882045) is an ongoing cardiovascular outcomes trial in participants with obesity and established cardiovascular disease.[21]

Preclinical data have also explored an oncology application: in murine obesity-cancer models, Retatrutide achieved a 14-fold reduction in pancreatic tumor volume and a 17-fold reduction in lung tumor volume, with 50% of lung-tumor mice rejecting tumors entirely.[8] Anti-tumor immune reprogramming persisted after drug withdrawal despite weight regain — a finding the clinical literature has not yet replicated in humans.

For Retatrutide dosage in clinical research and the TRIUMPH dose-escalation schedules, see the dedicated dosage page. For Retatrutide side effects as documented in Phase 2 and Phase 3 data, see the dedicated adverse-event page.

Is Retatrutide a Natural Hormone? Is Retatrutide a GLP-3?

Retatrutide is not a natural hormone. The three receptors it activates are stimulated in nature by GIP, GLP-1, and glucagon — all endogenous gut peptides — but Retatrutide itself is a synthetic, engineered molecule with a C20 fatty diacid conjugation that does not exist in the natural hormone milieu.[14]

The informal label “GLP-3” sometimes applied to Retatrutide is not an official pharmacological classification. The compound is accurately described as a triple GIP/GLP-1/glucagon receptor agonist, or a GGG triple agonist. “GLP-3” is a colloquial shorthand without biochemical precision.[14]

Retatrutide is also more potent at the human GIPR than endogenous GIP — its EC50 at GIPR is approximately 0.0643 nM, roughly 8.9 times more potent than the natural ligand. It is comparatively less potent than the natural ligands at the GLP-1R and GCGR (approximately 0.4× and 0.3× respectively).[14]

Who Developed Retatrutide?

Eli Lilly and Company (Indianapolis, Indiana, US) developed Retatrutide under the internal designation LY3437943. Eli Lilly’s deep expertise in GIP-based peptide research underpins the compound’s design. The TRIUMPH Phase 3 program is sponsored by Eli Lilly; NDA submission to the FDA is anticipated in Q4 2026 following the May 2026 TRIUMPH-1 readout.[21]

For a full reading of the triple-receptor mechanism of action, the Phase 2 and Phase 3 trial data, and the frequently asked questions about Retatrutide, follow the navigation above.