Retatrutide
Triple-acting incretin · 39 amino acids
A novel triple GIP/GLP-1/glucagon receptor agonist in Phase III trials, showing up to 24% body weight reduction in Phase II studies.
A novel triple GIP/GLP-1/glucagon receptor agonist in Phase III trials, showing up to 24% body weight reduction in Phase II studies.
Mechanism of Action
Retatrutide is a single molecule that simultaneously activates three incretin receptors: glucose-dependent insulinotropic polypeptide (GIP), glucagon-like peptide-1 (GLP-1), and glucagon receptors. This triple-acting mechanism is designed to leverage the complementary metabolic effects of all three pathways.
GLP-1 receptor activation promotes insulin secretion, suppresses glucagon release, slows gastric emptying, and reduces appetite through central nervous system pathways. GIP receptor activation enhances insulin secretion and may improve fat metabolism. Glucagon receptor activation — traditionally counterproductive for glucose control — appears to contribute to energy expenditure and fat oxidation when combined with GLP-1 agonism.
The unimolecular triple-agonist design allows coordinated activation of these pathways with a single weekly injection, potentially achieving greater metabolic efficacy than single or dual incretin agonists.
Reported Effects
Commonly Reported
- Up to 24.2% body weight reduction at 48 weeks in Phase II trials
- Significant improvements in HbA1c levels in type 2 diabetes
- Dose-dependent reduction in liver fat content
- Reduction in triglycerides and other lipid markers
Less Common Reports
- Improved blood pressure measurements
- Reduction in markers of systemic inflammation
- Potential benefits for non-alcoholic steatohepatitis (NASH)
- Enhanced metabolic flexibility observed in subgroup analyses
Phase II data from the phase 2 trial published in the New England Journal of Medicine (2023). Phase III TRIUMPH trials ongoing.
Next-generation metabolic health through multi-receptor agonism
Side Effects & Safety Profile
Low Concern
- Nausea (dose-dependent, typically transient)
- Vomiting
- Diarrhea
- Constipation
- Decreased appetite
Moderate Concern
- Injection site reactions
- Increased heart rate (modest)
- Gallbladder-related events
- Potential for pancreatitis (rare)
Serious
- Thyroid C-cell tumors in rodent studies (class effect, relevance to humans undetermined)
- Hypoglycemia risk when combined with insulin or sulfonylureas
- Gastrointestinal events requiring medical attention at higher doses
Retatrutide is an investigational compound. Not approved for human use outside of clinical trials.
Clinical Evidence
Retatrutide has been developed by Eli Lilly and Company with a focused clinical development program:
- Phase II (2023) — Published in NEJM. 338 participants with obesity or overweight. Up to 24.2% weight loss at 48 weeks with the highest dose (12mg). Dose-dependent effects on body weight, HbA1c, and liver fat.
- Phase III TRIUMPH program — Multiple ongoing trials evaluating retatrutide for obesity, type 2 diabetes, and obstructive sleep apnea
- Phase III TRANSCEND-NASH — Evaluating efficacy in non-alcoholic steatohepatitis
Results are being compared to existing GLP-1 agonists (semaglutide) and dual agonists (tirzepatide).
Discovery Timeline
- 2018 — Retatrutide (LY3437943) discovered by Eli Lilly researchers
- 2020–2022 — Phase I safety and dose-finding studies
- 2023 — Phase II results published in NEJM demonstrating 24% weight loss
- 2024 — Phase III TRIUMPH trials initiated across multiple indications
- 2025–2026 — Phase III trials ongoing; potential regulatory submission anticipated
Clinical trials showing unprecedented weight loss outcomes
Community Research Notes
The following testimonials are drawn from r/Peptides and r/Biohackers. Individual experiences vary. Nothing here constitutes medical advice.
"Way less food noise. Better control around food. This is huge." — r/Peptides
"I spent time learning how GLP-1s work, how fat loss actually happens, how protein impacts muscle. The more I understood, the better decisions I made." — r/Biohackers
"Minor strength loss and occasional nausea, but this peptide is amazing overall." — r/Biohackers
Frequently Asked Questions
Is retatrutide approved by the FDA? No. As of April 2026, retatrutide is still in Phase 3 clinical trials. It is not approved for human use. All current use is in research contexts.
How does retatrutide compare to semaglutide (Ozempic)? In head-to-head trial data, retatrutide produced significantly more weight loss than semaglutide at comparable timepoints. The triple agonist mechanism targets three receptors instead of one.
What dose do researchers use? Trial doses ranged from 1 mg to 12 mg weekly. Most research protocols start low (1 to 2 mg) and titrate up over several weeks to manage side effects.
Does retatrutide cause muscle loss? Any rapid weight loss can include some lean mass loss. Combining retatrutide with adequate protein intake and resistance training helps preserve muscle.
Can I stack retatrutide with other peptides? Research communities commonly stack retatrutide with mitochondrial and recovery peptides. See the stacking section below for common combinations.
Compounds That Pair Well
- MOTS-c — For enhanced mitochondrial energy and endurance during a calorie deficit.
- 5-Amino-1MQ — For metabolic acceleration without additional hormonal load.
- BPC-157 — For gut health support, especially if gastric side effects are present.
- GHK-Cu — For skin health during rapid weight loss to support skin elasticity.
- NAD+ — For cellular energy support during periods of reduced caloric intake.
Build Your Personalised Protocol
Retatrutide is one of many compounds available in the BioStack Generator. Explore metabolic health stacks with other GLP-1 and peptide compounds.