Retatrutide

Overview

Retatrutide, referred to in the research literature as LY3437943, is a 39-amino-acid synthetic peptide designed by researchers at Eli Lilly as a first-in-class molecule that simultaneously activates three receptors central to metabolic regulation: the GLP-1 receptor, the GIP receptor, and the glucagon receptor.

Most metabolic hormones act on a single receptor. Retatrutide is distinctive in engaging all three at once, each with its own role in glucose-dependent insulin signalling, satiety physiology, and hepatic energy handling. A C20 fatty diacid conjugated via a γ-Glu-AEEA linker at position 17 enables albumin binding and extends in-vivo half-life, which is what allows the once-weekly subcutaneous schedule used in the trials.

The literature now has two layers. Multiple randomised controlled phase 2 studies were published in The New England Journal of Medicine, The Lancet, and Nature Medicine, with dose-dependent outcomes on body weight, glucose regulation, and hepatic fat. From the confirmatory phase 3 programme, the first studies were published peer-reviewed in 2026: TRIUMPH-1 in The New England Journal of Medicine, and TRIUMPH-2 and TRANSCEND-T2D-1 in The Lancet. For TRIUMPH-3 and TRIUMPH-4 only manufacturer announcements exist as of the reference date.

Mechanism of action

Retatrutide is a first-in-class triple receptor agonist that simultaneously activates the GLP-1, GIP, and glucagon receptors. Its acylated structure binds albumin to extend in-vivo half-life, enabling sustained engagement of three complementary metabolic signalling axes.

Triple receptor engagement

• Simultaneous agonism of the GLP-1, GIP, and glucagon receptors from a single molecule
• GLP-1 and GIP receptor activity is implicated in glucose-dependent insulin signalling and satiety physiology
• Glucagon receptor activity is implicated in hepatic energy handling and whole-body energy expenditure

Structural design and pharmacokinetics

• 39-amino-acid synthetic peptide built on a GIP-like backbone with non-coded residues (Aib2, Aib20, α-Me-Leu13)
• A C20 fatty diacid conjugated via a γ-Glu-AEEA linker at position 17 enables albumin binding and a long in-vivo half-life
• C-terminal amidation and stabilising substitutions support proteolytic resistance
• Across the trials the compound was given subcutaneously, once weekly, at maintenance doses of 0.5–12 mg

Integrated metabolic signalling

• Combined activation of three receptors is an active and evolving area of mechanistic research
• Studied in models of glucose regulation, hepatic lipid handling, and whole-body energy balance
• Represents a research shift from single-pathway agonists toward multi-receptor metabolic modulators

Research findings

• Obesity phase 2 (Jastreboff et al., New England Journal of Medicine, 2023): double-blind, placebo-controlled, n=338, 48 weeks, subcutaneous once weekly; body weight fell by a mean of 24.2% in the 12 mg group, against 2.1% on placebo
• Type 2 diabetes phase 2 (Rosenstock et al., The Lancet, 2023): n=281; HbA1c fell by 2.02 percentage points at 24 weeks in the 12 mg group, against almost no change on placebo
• Hepatic steatosis substudy (Sanyal et al., Nature Medicine, 2024): n=98 with MASLD; liver fat fell by 82.4% at 24 weeks in the 12 mg group; in 86% of participants in that group liver fat was below the 5% threshold considered normal, against none on placebo
• Doses studied, as a fact about the trials: subcutaneous, once weekly, maintenance doses of 0.5–12 mg
• Across phase 2 and phase 3 the most reported observations were gastrointestinal (nausea, diarrhoea, constipation, vomiting), dose-dependent and mostly mild to moderate; in phase 3, dysaesthesia (an altered sensation in the skin) was also seen more often than on placebo, and in TRIUMPH-2 low blood pressure as well; the phase 2 study also saw a dose-dependent rise in heart rate, peaking around week 24 and declining afterwards
• The mechanism of action is structurally resolved, with characterised receptor pharmacology

Phase 3: published peer-reviewed (2026)

• TRIUMPH-1 (Jastreboff et al., New England Journal of Medicine, 2026): obesity/overweight without diabetes, n=2,339, 80 weeks, subcutaneous once weekly at 4, 9 or 12 mg; body weight fell by a mean of 17.6%, 23.7% and 25.0%, against 3.9% on placebo (main analysis, all participants)
• TRIUMPH-1, substudies (analysis of all participants): in 574 participants with knee osteoarthritis the WOMAC pain score fell by 3.4 to 4.1 points, against 2.5 on placebo; in 243 participants with obstructive sleep apnoea the apnoea-hypopnoea index fell by 22.8 to 34.3 events per hour, against 9.6 on placebo
• TRIUMPH-2 (Bellido et al., The Lancet, 2026): type 2 diabetes with obesity/overweight, n=1,152, 80 weeks; body weight fell by 11.9%, 16.8% and 18.8% (4, 9 and 12 mg), against 5.1% on placebo; dysaesthesia in 4%, 6% and 7% against 1%, low blood pressure in 1%, 5% and 6% against less than 1%
• TRANSCEND-T2D-1 (Bajaj et al., The Lancet, 2026): type 2 diabetes, retatrutide as the only medicine, n=537, 40 weeks; HbA1c fell by 1.69, 1.86 and 1.94 percentage points, against 0.81 on placebo; body weight by 11.5%, 13.9% and 15.3%, against 2.6%; no severe hypoglycaemia reported

Phase 3: reported by the manufacturer (not yet peer-reviewed)

• TRIUMPH-1, additional figures (Eli Lilly, 21 May 2026): using the way of counting that assumes continued use, body weight fell by 28.3% at 80 weeks in the 12 mg group, against 2.2% on placebo; in an extension to 104 weeks in 532 participants with a BMI of 35 or higher who had kept using the medicine until then, the reduction reached 30.3% in the group that had started on 12 mg
• TRIUMPH-3 (severe obesity with established cardiovascular disease, n=1,949; Eli Lilly, 23 July 2026): weight loss of up to 22.6% at 80 weeks, against 3.2% on placebo (with continued use); serious cardiovascular events, broad count: 44 against 52 (hazard ratio 0.82; 95% confidence interval 0.55 to 1.22); narrow count (cardiovascular death, heart attack, stroke): 27 against 23 (hazard ratio 1.12; 0.64 to 1.96); no demonstrated difference
• TRIUMPH-4 (obesity/overweight with knee osteoarthritis, n=445; Eli Lilly, 11 December 2025): at 68 weeks body weight fell by 23.7% in the 12 mg group when all participants are counted, against 4.6% on placebo (28.7% against 2.1% with continued use), alongside a reduction in participant-reported knee pain; dysaesthesia in 20.9% of the 12 mg group, against 0.7% on placebo
• These figures come from manufacturer press releases and are not yet peer-reviewed

Research context

Retatrutide sits at the upper end of growing clinical evidence: consistently positive phase 2 results across multiple research areas, peer-reviewed phase 3 studies in thousands of participants, a structurally resolved mechanism of action, and a well-characterised safety profile.

As a first-in-class triple receptor agonist, it has become a reference point in research on multi-receptor metabolic signalling.

Regulatory status, as a fact about the manufacturer and the regulator: retatrutide is not approved anywhere; Eli Lilly has announced it intends to submit a Biologics License Application (BLA) to the US FDA in the first quarter of 2027.

It illustrates a broader scientific shift: from molecules acting on a single pathway toward compounds engaging several metabolic axes at once.

Open questions

The results are strong and the formal regulatory review has yet to begin: the remaining phase 3 publications, the direct comparisons and the long-term outcomes study are what remain outstanding.

• Not all phase 3 studies have been published: for TRIUMPH-3 and TRIUMPH-4 only manufacturer announcements exist
• Whether the observed weight reduction translates into fewer cardiovascular and kidney events is being tested in a separate long-term outcomes study that has no results yet
• The long-term safety profile beyond the reported trial horizons is still being built
• The relative contribution of each receptor (GLP-1, GIP, glucagon) to the observed metabolic outcomes is not fully resolved
• Direct comparisons with established mono- and dual-agonists (including tirzepatide and semaglutide) are still running and have no published results yet

Research outlook

Peer-reviewed publication of the remaining TRIUMPH studies (TRIUMPH-3 and TRIUMPH-4)

The announced regulatory application (BLA, first quarter of 2027) and the review that follows

The long-term cardiovascular and kidney outcomes study

Deeper mechanistic dissection of how combined GLP-1 / GIP / glucagon agonism produces integrated metabolic outcomes

Results of the ongoing direct comparisons with tirzepatide and semaglutide

Scientific interest

First-in-class triple agonist of the GIP, GLP-1 and glucagon receptors

Reference compound for research on multi-receptor metabolic signalling

Structurally resolved mechanism with consistent phase 2 data and peer-reviewed phase 3 studies

Model for studying how combined activation of metabolic receptors relates to energy and glucose regulation

Specifications

References

1. A new glucagon and GLP-1 co-agonist eliminates obesity in rodents. · Day JW, et al · Nat Chem Biol · 2009
2. The metabolic actions of glucagon revisited. · Habegger KM, et al · Nat Rev Endocrinol · 2010
3. Glucagon receptor knockout prevents insulin-deficient type 1 diabetes in mice. · Lee Y, et al · Diabetes · 2011
4. Coadministration of glucagon-like peptide-1 during glucagon infusion in humans results in increased energy expenditure and amelioration of hyperglycemia. · Tan TM, et al · Diabetes · 2013
5. Glucagon increases energy expenditure independently of brown adipose tissue activation in humans. · Salem V, et al · Diabetes Obes Metab · 2016
6. The New Biology and Pharmacology of Glucagon. · Müller TD, et al · Physiol Rev · 2017
7. Treatment with LY2409021, a glucagon receptor antagonist, increases liver fat in patients with type 2 diabetes. · Guzman CB, et al · Diabetes Obes Metab · 2017
8. The Liver-α-Cell Axis and Type 2 Diabetes. · Wewer Albrechtsen NJ, et al · Endocr Rev · 2019
9. Effects of Cotadutide on Metabolic and Hepatic Parameters in Adults With Overweight or Obesity and Type 2 Diabetes: A 54-Week Randomized Phase 2b Study. · Nahra R, et al · Diabetes Care · 2021
10. LY3437943, a novel triple glucagon, GIP, and GLP-1 receptor agonist for glycemic control and weight loss: From discovery to clinical proof of concept · Coskun T, Urva S, Roell WC, et al. · Cell Metabolism · 2022
11. Retatrutide, a GIP, GLP-1 and glucagon receptor agonist, for people with type 2 diabetes: a randomised, double-blind, placebo and active comparator-controlled phase 2 trial · Rosenstock J, Frias J, Jastreboff AM, et al. · The Lancet · 2023
12. Triple-Hormone-Receptor Agonist Retatrutide for Obesity — A Phase 2 Trial · Jastreboff AM, Kaplan LM, Frias JP, et al. · The New England Journal of Medicine · 2023
13. A Phase 2 Randomized Trial of Survodutide in MASH and Fibrosis. · Sanyal AJ, et al · N Engl J Med · 2024
14. Glucagon and GLP-1 receptor dual agonist survodutide for obesity: a randomised, double-blind, placebo-controlled, dose-finding phase 2 trial. · le Roux CW, et al · Lancet Diabetes Endocrinol · 2024
15. Triple hormone receptor agonist retatrutide for metabolic dysfunction-associated steatotic liver disease: a randomized phase 2a trial · Sanyal AJ, Bedossa P, Fraessdorf M, et al. · Nature Medicine · 2024
16. Once-Weekly Mazdutide in Chinese Adults with Obesity or Overweight. · Ji L, et al · N Engl J Med · 2025
17. Retatrutide: A Game Changer in Obesity Pharmacotherapy · Katsi V, Koutsopoulos G, Fragoulis C, Dimitriadis K, Tsioufis K. · Biomolecules · 2025
18. Retatrutide in adults with obesity and type 2 diabetes (TRIUMPH-2): a double-blind, parallel-group, randomised, placebo-controlled, phase 3 trial. · Bellido V, et al · Lancet · 2026
19. Retatrutide, a Triple Hormone Receptor Agonist, for Treatment of Obesity · Jastreboff AM, Kaplan LM, Davies MJ, et al. · The New England Journal of Medicine · 2026
20. Efficacy and safety of retatrutide, a GIP, GLP-1, and glucagon receptor agonist, in people with type 2 diabetes and inadequate glycaemic control with diet and exercise (TRANSCEND-T2D-1): a double-blind, randomised, phase 3 trial. · Bajaj HS, et al · Lancet · 2026

Availability

In stock · Batch PEP-RET-2026-01 · HPLC 99.17 % · released 20 Jun 2026

• Retatrutide 10 mg · 20 mg · product page with price and batch CoA