# Retatrutide: Triple-Agonist Research Digest | Retatrutide Dr

> Retatrutide is an investigational triple GIP/GLP-1/glucagon receptor agonist. Phase 3 data: 28.3% mean body weight reduction at 80 weeks. Research summaries, cited from the clinical literature.

## 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].

## 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. GIP receptor activation augments glucose-stimulated insulin secretion and modulates adipocyte lipolysis signaling. Glucagon receptor activation 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 (n=2,339, 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 [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. Secondary indications include type 2 diabetes, MASLD/MASH, and cardiovascular outcomes in participants with established cardiovascular disease [21].

The TRIUMPH Phase 3 program includes TRIUMPH-1 (pivotal obesity, n=2,339, 80 weeks) [9], TRIUMPH-4 (obesity + knee osteoarthritis, 68 weeks; 28.7% weight reduction + 75.8% WOMAC knee pain reduction at 12 mg) [10], TRIUMPH-3 (cardiovascular outcomes, NCT05882045) [21], and TRIUMPH-OUTCOMES (NCT06383390).

Preclinical data in murine obesity-cancer models showed a 14-fold reduction in pancreatic tumor volume and a 17-fold reduction in lung tumor volume [8].

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

Retatrutide is not a natural hormone. It is a synthetic, engineered molecule. The "GLP-3" label is not an official pharmacological classification — the compound is accurately described as a triple GIP/GLP-1/glucagon receptor agonist [14].

Retatrutide is approximately 8.9 times more potent at the human GIPR than endogenous GIP (EC50 ~0.0643 nM). It is comparatively less potent than the natural ligands at GLP-1R and GCGR [14].

## Who Developed Retatrutide?

Eli Lilly and Company (Indianapolis, Indiana, US), internal designation LY3437943. NDA submission to the FDA is anticipated in Q4 2026 [21].

## References

[1] Jastreboff AM, et al. Triple–Hormone-Receptor Agonist Retatrutide for Obesity — A Phase 2 Trial. N Engl J Med. 2023;389:514-526. DOI: 10.1056/NEJMoa2301972
[4] Rosenstock J, et al. Retatrutide for type 2 diabetes. Lancet. 2023. DOI: 10.1016/S0140-6736(23)01053-X
[5] Urva S, et al. LY3437943, a novel triple GIP, GLP-1, and glucagon receptor agonist. Lancet. 2022;400:1869-1881.
[6] Li W, et al. Structural insights into the triple agonism at GLP-1R, GIPR and GCGR. Cell Discovery. 2024.
[7] Sanyal AJ, et al. Triple hormone receptor agonist retatrutide for MASLD. Nat Med. 2024.
[8] Marathe SJ, et al. Incretin triple agonist retatrutide alleviates obesity-associated cancer progression. NPJ Metab Health Dis. 2025.
[9] Eli Lilly. TRIUMPH-1 Phase 3 press release. PR Newswire. 2026.
[10] Eli Lilly. TRIUMPH-4 Phase 3 press release. Eli Lilly Investor Relations. 2025.
[12] Goldney J, et al. Triple Agonism Based Therapies for Obesity. Curr Cardiovasc Risk Rep. 2025.
[14] Katsi V, et al. Retatrutide—A Game Changer in Obesity Pharmacotherapy. Biomolecules. 2025.
[21] Eli Lilly. TRIUMPH-3 ClinicalTrials.gov NCT05882045. 2023.

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Plain-language summaries of the Phase 2 and Phase 3 Retatrutide trial record — independent, cited, and not a clinical service.