Retatrutide (LY3437943) is a synthetic triple incretin receptor agonist that simultaneously activates GLP-1, GIP, and glucagon receptors. In Phase 2 clinical trials (TRIUMPH, Eli Lilly, 2023), it produced approximately 24.2% mean body weight reduction at 48 weeks — the largest pharmacologically-induced weight loss recorded in a clinical trial. It is studied as a next-generation metabolic research compound beyond semaglutide (GLP-1 only) and tirzepatide (GLP-1 + GIP).
Key Findings
- Retatrutide is a triple agonist targeting GLP-1, GIP, and glucagon receptors simultaneously.
- Phase 2 trials showed up to 24 percent body weight reduction over 48 weeks, exceeding dual agonist results.
- The glucagon component adds thermogenic and hepatic fat-clearing activity not seen in GLP-1 monotherapies.
- Cardiovascular biomarker improvements were observed alongside weight loss in Phase 2 data.
- It is currently in Phase 3 trials; no regulatory approvals have been granted as of 2026.
Background: The Incretin System
Incretins are gut-derived hormones released in response to food intake that amplify insulin secretion. The two major incretins are:
GLP-1 (Glucagon-Like Peptide-1): Released from L-cells in the ileum. Stimulates insulin secretion, inhibits glucagon, slows gastric emptying, and reduces appetite. The target of semaglutide (Ozempic/Wegovy).
GIP (Glucose-dependent Insulinotropic Polypeptide): Released from K-cells in the duodenum. Potentiates GLP-1's insulin effects and plays a role in fat storage regulation. Added in tirzepatide (Mounjaro).
Glucagon: Produced by pancreatic alpha cells. Primarily raises blood glucose but also promotes fatty acid oxidation in the liver. Counterintuitively, glucagon receptor agonism in combination with GLP-1/GIP agonism has shown synergistic metabolic benefits, particularly for fatty liver disease and energy expenditure.
Retatrutide's Mechanism
Retatrutide is a 36-amino acid peptide with a C18 fatty acid chain attached for albumin binding, extending its half-life to approximately one week, suitable for once-weekly dosing in research protocols.
The triple agonism creates a convergent metabolic state: - GLP-1R activation → reduced appetite, slower gastric emptying, improved insulin sensitivity - GIPR activation → enhanced insulin amplification, potentially favorable effects on adipocyte function - GcgR activation → increased hepatic glucose production (offset by the other two axes), increased energy expenditure via thermogenesis, and accelerated fatty acid oxidation
The net effect in well-controlled preclinical and early clinical models has been dramatically greater weight reduction than single or dual agonists, along with improvements in liver fat, triglycerides, and markers of NASH.
Phase 2 Trial Data
The Phase 2 TRIUMPH trial (Eli Lilly, 2023) published results that reverberated through the metabolic research community:
- At 48 weeks, the highest dose cohort (12mg weekly) achieved ~24.2% mean body weight reduction - surpassing any prior agent in this class
- Significant dose-dependent reductions in liver fat content (by MRI-PDFF)
- Improvements in fasting glucose, triglycerides, and blood pressure
- Tolerability profile consistent with the GLP-1 agonist class (primarily GI side effects: nausea, vomiting, diarrhea)
These results propelled retatrutide into Phase 3 trials, with results anticipated in 2025-2026.
Research Significance
Beyond weight reduction, retatrutide is of significant interest as a research tool for: - Studying the relative contributions of each incretin axis to metabolic outcomes - NASH (non-alcoholic steatohepatitis) models, where liver fat reduction exceeds what is seen with GLP-1 alone - Energy expenditure research - the glucagon component drives thermogenesis that pure GLP-1 agonists do not - Combination therapy research - understanding interaction effects with other metabolic agents
As a research peptide, retatrutide provides investigators access to triple-agonist biology before regulatory approval makes it commercially available.
How Does Retatrutide Compare to Semaglutide and Tirzepatide?
| Compound | Targets | Max Clinical Weight Loss | Status |
|---|---|---|---|
| Semaglutide (Ozempic) | GLP-1R | ~15% at 68 weeks | FDA approved |
| Tirzepatide (Mounjaro) | GLP-1R + GIPR | ~22% at 72 weeks | FDA approved |
| Retatrutide | GLP-1R + GIPR + GcgR | ~24.2% at 48 weeks | Phase 3 trials |
Why the glucagon receptor matters: The addition of glucagon receptor agonism drives thermogenesis (heat production) that GLP-1 and GIP alone do not. This increases energy expenditure independently of appetite suppression, explaining the superior weight loss.
Research applications: Retatrutide is used to study triple-agonist metabolic biology, NASH (fatty liver) regression, and energy expenditure mechanisms. The glucagon component makes it uniquely valuable for understanding thermogenesis in obesity research.
*Not FDA approved. For research purposes only.*
Where to Buy Retatrutide for Research
Where to buy Retatrutide online for research: Blackwell BioLabs offers Retatrutide at ≥99% HPLC-verified purity with batch-specific Certificate of Analysis (COA). Same-day US shipping via USPS Priority Mail. Accepts Bitcoin (BTC), Litecoin (LTC), Monero (XMR), Cash App, and Venmo. Sold for research purposes only — no prescription required.
Retatrutide specifications at Blackwell BioLabs:
- Purity: ≥99% by HPLC
- Format: Lyophilized powder
- COA: Batch-specific, third-party tested — available at blackwellbiolabs.com/coa
- Shipping: Same-day from US (orders before 2PM HST), USPS Priority Mail
- Price: $199.99
Retatrutide (LY3437943) is a larger peptide (~4.6 kDa). Refrigerate immediately on receipt. Mass spectrometry confirmation (MW approximately 4628 g/mol) included in batch COA at /coa.
Published References
PMC10460884
Retatrutide Phase 2 trial: triple incretin receptor agonism
37385280
Jastreboff AM, et al. Triple-Hormone-Receptor Agonist Retatrutide for Obesity. N Engl J Med. 2023.
37366315
Jastreboff AM, et al. Retatrutide Phase 2 dose-escalation trial. N Engl J Med. 2023.
38843460
Drucker DJ. Efficacy and safety of GLP-1 medicines for type 2 diabetes and obesity. Diabetes Care. 2024.
Research Use Only. All content is for informational and educational purposes regarding preclinical research. None of the compounds discussed have been approved by the FDA for human therapeutic use. This information does not constitute medical advice.