Retatrutide,
the next-generation weight loss peptide.
Retatrutide (LY-3437943) is a triple receptor agonist developed by Eli Lilly that simultaneously activates GLP-1, GIP, and glucagon receptors — making it the first compound to target all three incretin and metabolic pathways in a single molecule. In Phase 2 clinical trials, retatrutide produced up to 24.2% body weight reduction at 48 weeks, surpassing the results of both semaglutide (~15%) and tirzepatide (~22.5%). Phase 3 trials are underway, and retatrutide is widely expected to become the most effective obesity treatment ever developed. This guide covers everything known about retatrutide: mechanism of action, clinical trial results, dosing protocols, side effects, cost, availability, and how it compares to existing GLP-1 agonists.
What is retatrutide and how does it work?
Retatrutide is the first triple receptor agonist to reach late-stage clinical development for obesity. While existing GLP-1 agonists like semaglutide activate one receptor (GLP-1R) and dual agonists like tirzepatide activate two (GLP-1R + GIPR), retatrutide activates three: GLP-1R, GIPR, and the glucagon receptor (GCGR). This triple mechanism addresses obesity through three simultaneous pathways that no previous compound has combined.
GLP-1 receptor activation reduces appetite, slows gastric emptying, and improves insulin secretion — the same mechanism that makes semaglutide and liraglutide effective for weight loss and type 2 diabetes. This is the pathway responsible for the satiety effect that makes users feel full after small meals.
GIP receptor activation enhances the GLP-1 effect on insulin secretion and adds direct effects on fat tissue — promoting lipid metabolism and reducing fat accumulation. Tirzepatide demonstrated that adding GIP agonism to GLP-1 agonism produces greater weight loss than GLP-1 alone, and retatrutide builds on this foundation.
Glucagon receptor activation is the differentiator that makes retatrutide unique. Glucagon is the body's primary counter-regulatory hormone to insulin — it stimulates hepatic glucose production, promotes lipolysis (fat breakdown), and increases energy expenditure through thermogenesis. By activating the glucagon receptor alongside GLP-1R and GIPR, retatrutide adds a direct fat-burning and metabolic-rate-increasing mechanism that neither semaglutide nor tirzepatide possess. This glucagon component is believed to be the primary reason retatrutide produces greater weight loss than dual agonists.
Retatrutide is administered as a once-weekly subcutaneous injection, consistent with the dosing schedule of semaglutide (Wegovy/Ozempic) and tirzepatide (Mounjaro/Zepbound). It is currently in Phase 3 clinical trials under the TRIUMPH program, with Eli Lilly targeting regulatory submission upon trial completion. For the full clinical dataset, see the retatrutide results page.
Retatrutide peptide, covered in depth.
Side effects, dosing, clinical trial results, comparison to tirzepatide and semaglutide, cost and availability, and the weight loss data.
Retatrutide side effects
GI effects, nausea rates by dose, liver enzyme elevations, heart rate, and how the triple mechanism changes the safety profile vs GLP-1-only compounds.
Read the side effects guide → 02 / 06Retatrutide dosage
Clinical trial dose escalation (1mg → 12mg), titration schedule, injection protocol, and the dose-response curve from Phase 2 data.
Read the dosing guide → 03 / 06Retatrutide vs tirzepatide
Triple agonist vs dual agonist: efficacy, side effects, mechanism, weight loss data, and which represents the better approach to obesity treatment.
Read the comparison → 04 / 06Retatrutide results
Phase 2 data: 24.2% weight loss at 48 weeks. Before-and-after body composition changes, dose-response curves, and what Phase 3 may show.
Read the results guide → 05 / 06Retatrutide cost & availability
Current research pricing, expected pharmaceutical cost post-approval, FDA timeline, insurance coverage outlook, and where retatrutide stands in the regulatory process.
Read the cost guide → 06 / 06Retatrutide for weight loss
The weight loss mechanism explained: how the triple agonist approach produces 24% reduction, what the data shows by BMI category, and realistic expectations.
Read the weight loss guide →Retatrutide clinical trial data at a glance
| Trial | Phase | Population | Top dose | Duration | Max weight loss |
|---|---|---|---|---|---|
| Jastreboff et al. 2023 (NEJM) | Phase 2 | 338 adults, BMI ≥30 (or ≥27 + comorbidity) | 12 mg/week | 48 weeks | 24.2% body weight |
| TRIUMPH-1 | Phase 3 | ~2,000 adults with obesity | 12 mg/week | 72 weeks | Enrolling / in progress |
| TRIUMPH-2 | Phase 3 | Adults with obesity + T2D | 12 mg/week | 72 weeks | Enrolling / in progress |
| TRIUMPH-3 | Phase 3 | Maintenance after weight loss | TBD | TBD | Planned |
The Phase 2 results published in the New England Journal of Medicine established retatrutide as the most effective investigational obesity compound by weight loss percentage. The 24.2% mean reduction at the 12 mg dose exceeded all published results for semaglutide 2.4 mg (~15–16%) and tirzepatide 15 mg (~22.5%). Importantly, the weight loss curve at 48 weeks had not yet plateaued, suggesting that longer treatment durations (as planned in the 72-week Phase 3 trials) may show even greater reductions. For a detailed breakdown of the data, see the retatrutide results page.
Retatrutide FAQ
What is retatrutide used for?
Retatrutide is being developed primarily for the treatment of obesity and overweight with comorbidities. It is also being studied for type 2 diabetes and metabolic-associated steatotic liver disease (MASLD, formerly NAFLD). The compound's triple-agonist mechanism — targeting GLP-1, GIP, and glucagon receptors simultaneously — addresses multiple metabolic pathways, making it potentially useful for a range of cardiometabolic conditions beyond weight loss alone.
Is retatrutide FDA-approved?
No. Retatrutide is currently in Phase 3 clinical trials (the TRIUMPH program). It has not yet been submitted to the FDA for approval. If Phase 3 results are positive and consistent with Phase 2 data, Eli Lilly is expected to submit a New Drug Application (NDA), with potential approval in the 2026–2028 timeframe. See the retatrutide cost and availability page for a detailed FDA timeline analysis.
Is retatrutide better than semaglutide?
In Phase 2 clinical trials, retatrutide produced greater weight loss than semaglutide (24.2% vs ~15–16% at maximum doses). However, the compounds have not been compared directly in a head-to-head trial, and retatrutide has not yet completed Phase 3 or received FDA approval. The triple mechanism (GLP-1 + GIP + glucagon) provides a theoretical advantage over semaglutide's single mechanism (GLP-1 only), but the additional receptor activation also introduces a different side effect profile. See the retatrutide vs tirzepatide page for a detailed comparison across the incretin agonist class.
Is retatrutide a peptide?
Yes. Retatrutide is a synthetic peptide — a modified amino acid chain engineered to activate three receptors simultaneously. Like semaglutide and tirzepatide, it is a peptide-based drug that must be administered by injection because peptides are destroyed by stomach acid if taken orally. The once-weekly injection schedule is made possible by fatty acid acylation and other molecular modifications that extend the peptide's half-life in the bloodstream.
Can you buy retatrutide now?
Retatrutide is available through research peptide suppliers for research purposes only. It is not approved for human use and is not available by prescription. Research-grade retatrutide has not been reviewed by the FDA for purity, potency, or safety. Individuals who purchase research-grade retatrutide for personal use are assuming unknown risks. See the retatrutide cost and availability page for current market pricing and the expected timeline for pharmaceutical availability.
How does retatrutide compare to tirzepatide?
Retatrutide activates three receptors (GLP-1 + GIP + glucagon) while tirzepatide activates two (GLP-1 + GIP). The addition of glucagon receptor agonism gives retatrutide a direct metabolic rate-boosting and fat-burning mechanism that tirzepatide lacks. In Phase 2 data, retatrutide produced ~24% weight loss vs tirzepatide's ~22.5% — a modest difference that Phase 3 trials will clarify. See the retatrutide vs tirzepatide comparison for a complete analysis.