Retatrutide (LY3437943) is a first-in-class triple-receptor agonist peptide that simultaneously activates GLP-1, GIP, and glucagon receptors. Developed by Eli Lilly, it represents a generational advance over single-agonist (semaglutide) and dual-agonist (tirzepatide) compounds — and its Phase 2 clinical data, published in The New England Journal of Medicine, produced the highest weight reduction ever recorded in an obesity trial.
This guide covers retatrutide’s unique triple-agonist mechanism, published clinical trial data, how it compares to its predecessors, and practical research information.
The Triple-Agonist Mechanism
Every incretin-based peptide before retatrutide worked by reducing energy intake — making subjects eat less through appetite suppression and delayed gastric emptying. Retatrutide does this too, but adds something fundamentally new: it also increases energy expenditure. This dual-action approach (eat less + burn more) is what distinguishes it mechanistically and may explain its superior clinical outcomes.
GLP-1 Receptor Activation
The GLP-1 component suppresses appetite through central nervous system signaling, delays gastric emptying (creating prolonged satiety), and promotes glucose-dependent insulin secretion. This is the same mechanism that made semaglutide effective, and retatrutide retains it fully.
GIP Receptor Activation
The GIP (glucose-dependent insulinotropic polypeptide) receptor component enhances insulin secretion beyond what GLP-1 alone achieves and appears to influence lipid metabolism and adipose tissue function. This is the same addition that made tirzepatide more effective than semaglutide, and retatrutide retains it as well.
Glucagon Receptor Activation — The Breakthrough
The glucagon receptor component is retatrutide’s defining innovation. Glucagon receptor activation stimulates hepatic lipolysis (fat breakdown in the liver), increases fatty acid oxidation (burning fat for energy), elevates basal energy expenditure (higher resting metabolic rate), promotes thermogenesis (heat generation from fat metabolism), and drives hepatic glucose output regulation.
This means retatrutide doesn’t just reduce the calories coming in — it actively increases the calories going out. In an energy balance equation (weight change = energy in – energy out), retatrutide pushes both sides simultaneously.
Published Clinical Trial Data
Phase 2 Trial (NEJM, 2023)
The landmark Phase 2 trial, published in The New England Journal of Medicine by Jastreboff et al., enrolled 338 adults with obesity and produced results that exceeded all prior incretin-based therapies:
- 24.2% mean weight loss at the highest dose (12mg) over just 48 weeks — approximately 57.8 pounds in an average participant
- Over 90% of participants in the 12mg group lost at least 10% of their baseline body weight
- Approximately 25% of participants in the 12mg group lost 30% or more of their baseline weight
- No weight-loss plateau was observed at study end — participants were still losing weight when the trial concluded at 48 weeks, suggesting the full efficacy potential had not yet been reached
- Dose-dependent reductions in blood pressure, triglycerides, LDL-cholesterol, and HbA1c
For context: semaglutide achieved ~16% weight loss at 68 weeks, and tirzepatide achieved ~22.5% at 72 weeks. Retatrutide surpassed both — in a shorter timeframe — and hadn’t plateaued.
Phase 3 TRIUMPH Program
Eli Lilly’s Phase 3 program (TRIUMPH trials) is the largest clinical development program for retatrutide. Key results reported to date:
TRIUMPH-4: Average weight loss of approximately 71.2 lbs (32.3 kg) with the 12mg dose over 68 weeks. Concurrent improvements in knee osteoarthritis pain scores were also reported, suggesting benefits beyond weight reduction.
TRANSCEND: Evaluated retatrutide’s effects on metabolic dysfunction-associated steatohepatitis (MASH, formerly NASH). Results showed significant liver fat reduction, consistent with the glucagon receptor’s role in hepatic lipid metabolism.
Safety Profile
Retatrutide’s safety data from clinical trials shows a profile consistent with the incretin class:
Gastrointestinal effects are the most commonly reported — nausea, diarrhea, vomiting, and constipation occur more frequently at higher doses. These effects are generally dose-dependent, transient, and diminish with continued treatment. This is consistent with semaglutide and tirzepatide.
Cutaneous hyperesthesia (skin sensitivity) was reported in approximately 7% of retatrutide participants versus 1% for placebo — an effect not commonly seen with semaglutide or tirzepatide. This appears to be unique to retatrutide and may relate to the glucagon receptor component.
No clinically significant hypoglycemia was reported. No cases of medullary thyroid cancer or C-cell hyperplasia were observed. Cardiovascular safety outcomes remain under evaluation in ongoing Phase 3 trials.
Molecular Structure
Identifier: LY3437943 | Developer: Eli Lilly | Structure: GIP-based backbone engineered with GLP-1 and glucagon receptor activity, plus a C20 fatty diacid side chain for extended half-life | Administration: Once-weekly subcutaneous injection | Half-life: Approximately 6 days (supporting weekly dosing)
The C20 fatty diacid modification enables albumin binding in circulation, extending the half-life to approximately 6 days and making once-weekly dosing feasible — the same pharmacokinetic strategy used in semaglutide (C18 fatty acid) and tirzepatide (C20 fatty diacid).
Current Regulatory Status
Retatrutide is not FDA-approved. It is currently in Phase 3 clinical trials (TRIUMPH program) for obesity and related metabolic conditions. Eli Lilly has not announced an expected approval date, but the Phase 3 program is extensive, suggesting the company is pursuing a broad label.
For researchers, this means retatrutide is available exclusively as a research compound — not through pharmacies or prescription. PSPeptides carries research-grade retatrutide manufactured in the US at 99%+ verified purity.
Buy Retatrutide — Available in 5mg, 10mg, 20mg, 30mg →
Frequently Asked Questions
How is retatrutide different from semaglutide?
Semaglutide activates only the GLP-1 receptor (appetite suppression). Retatrutide activates three receptors: GLP-1 (appetite), GIP (enhanced insulin/lipid metabolism), and glucagon (increased energy expenditure and fat oxidation). The glucagon component means retatrutide both reduces energy intake AND increases energy output.
Is retatrutide FDA-approved?
No. Retatrutide is in Phase 3 clinical trials. It is available for laboratory research purposes only.
What sizes does PSPeptides offer?
Retatrutide is available in 5mg ($39.99), 10mg, 20mg, and 30mg ($119.99) vials, all at 99%+ verified purity with independent third-party testing documentation.
References
- Jastreboff AM, et al. Triple–Hormone-Receptor Agonist Retatrutide for Obesity — A Phase 2 Trial. N Engl J Med. 2023;389(6):514-526.
- Coskun T, et al. LY3437943, a novel triple glucagon, GIP, and GLP-1 receptor agonist for glycemic control and weight loss. Cell Metab. 2022;34(9):1234-1247.e9.
This product is intended for laboratory research use only. Not for human consumption.
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