Quick Facts
Plain-English Summary
Retatrutide is a synthetic 36-amino acid peptide developed by Eli Lilly that simultaneously activates three distinct hormone receptors: the GIP receptor, the GLP-1 receptor, and the glucagon receptor. This triple agonism places it in a pharmacological class of its own — no other approved or late-stage agent targets all three pathways simultaneously. The compound is sometimes referred to informally as GLP-3, though this is a colloquial designation and not an official pharmacological classification.
The rationale for targeting all three receptors is additive and partially complementary. GLP-1 receptor agonism drives appetite suppression and slows gastric emptying. GIP receptor agonism augments insulin secretion in a glucose-dependent manner and may reduce the GI side effects associated with GLP-1 agonists alone. The glucagon receptor component is the most pharmacologically distinctive feature: glucagon receptor activation increases energy expenditure and promotes hepatic fat mobilisation, effects that are not achievable through GLP-1 or GIP pathways alone.
In the landmark Phase II trial published in the New England Journal of Medicine in 2023 (Jastreboff et al.), adults with obesity who received the highest dose of Retatrutide (12 mg weekly) achieved a mean body weight reduction of 24.2% at 48 weeks. This was the largest weight-loss signal reported for any pharmaceutical agent in its class at the time of publication, surpassing the 15–17% reductions observed with semaglutide and tirzepatide in comparable trial designs.
Phase III status: As of August 2026, Retatrutide is undergoing Phase III evaluation under Eli Lilly's TRIUMPH clinical programme. It has not received FDA, EMA, or Health Canada approval for any indication. All efficacy and safety data currently available derive from Phase II studies. Phase III results and regulatory submissions are anticipated but not yet published.
Outside of clinical trial settings, Retatrutide is not available as an approved therapy. It is sold in research contexts in some jurisdictions, but it is not legally compounded for human use at scale, and its regulatory status is research-only outside formal trial participation. Community claims describing it as approved, equivalent to Ozempic, or safe for unsupervised use are inaccurate.
Mechanism of Action
Proposed mechanisms below are derived from in vitro and rodent studies only. No mechanistic pathway has been validated in a controlled human study.
All mechanistic data is derived from in vitro or rodent studies. Applicability of these pathways in humans is not established.
Animal Data
| Model | Finding | ICPS Status |
|---|---|---|
| Diet-induced obese (DIO) rodents | Significant body weight reduction and improved insulin sensitivity at therapeutic dose ranges. Glucagon receptor component contributed additive weight loss beyond GLP-1/GIP dual agonism in head-to-head comparisons. | Preclinical |
| Non-human primate metabolic model | Dose-dependent weight reduction and reduction in hepatic triglyceride content. Cardiovascular safety signals (heart rate, blood pressure) within acceptable range at clinical dose equivalents. | Preclinical |
| Hepatic steatosis model (rodent) | GCGR component drove significant reduction in liver fat fraction versus GLP-1 agonist alone. Proposed mechanism: upregulation of hepatic fatty acid oxidation and suppression of de novo lipogenesis. | Preclinical |
| Receptor binding characterisation (in vitro) | Confirmed balanced agonism across GIPR, GLP-1R, and GCGR. Fatty acid conjugation at Lys17 (C18 di-acid) confers albumin binding and achieves ~6-day half-life consistent with once-weekly dosing. | In Vitro |
No finding from this section has been replicated in a controlled human trial. Animal-to-human translation for peptides is uncertain and cannot be assumed.
Human Trials
| Trial | Population | Status | ICPS Status |
|---|---|---|---|
| Phase II — NEJM 2023 Jastreboff et al. | 338 adults with obesity (BMI ≥ 30) or overweight with comorbidity; randomised, double-blind, placebo-controlled; doses 1–12 mg weekly; 48 weeks. NEJM 2023 ↗ | — | Published |
| Phase II — Glycaemic sub-analysis | Subset of Phase II participants with type 2 diabetes or pre-diabetes. HbA1c reduction, fasting glucose, and insulin sensitivity endpoints. | — | Sub-analysis |
| Phase III — TRIUMPH-1 Eli Lilly TRIUMPH programme | Large-scale randomised controlled trial in adults with obesity. Primary endpoint: body weight reduction at 52 weeks. Secondary endpoints include cardiometabolic markers, MASLD endpoints, and safety. | — | Phase III — Ongoing |
| Phase III — TRIUMPH-2 and TRIUMPH-T2D | TRIUMPH-2 targets obesity with cardiovascular risk; TRIUMPH-T2D targets type 2 diabetes as primary population. Both under Eli Lilly sponsorship. | — | Phase III — Ongoing |
Retatrutide has no FDA, EMA, or Health Canada–approved indications and no published Phase III trial data for any condition as of 2026.
Safety & Side Effects
Nausea, vomiting, diarrhoea, and constipation were the most common adverse events in Phase II, consistent with the GLP-1 receptor class. Rates increased with dose escalation. Discontinuation due to GI adverse events occurred in approximately 16% of the highest-dose group. GIP receptor co-agonism appears to partially mitigate nausea vs. GLP-1 alone, but does not eliminate it.
The glucagon receptor component is pharmacologically novel in the context of chronic weight management therapy. Prolonged GCGR agonism has theoretical implications for: hepatic glucose output, ketogenesis during caloric restriction, cardiovascular effects (heart rate, blood pressure), and potential effects on bone metabolism. Long-term cardiovascular outcome data from Phase III is required to fully characterise this risk profile.
- Nausea (most common at dose escalation)
- Vomiting and diarrhoea
- Constipation
- Injection site reactions (mild)
- Elevated heart rate (mild, class-consistent)
- No pancreatitis cases reported in Phase II
- Personal or family history of medullary thyroid carcinoma
- MEN-2 syndrome (GLP-1R class contraindication)
- Pregnancy or breastfeeding
- Severe hepatic or renal impairment
- Paediatric populations (no data)
- Unsupervised use outside clinical setting
Retatrutide is not approved by the FDA, EMA, or Health Canada for any medical indication. It is classified as a research compound and is not legal for human therapeutic use in most jurisdictions. Procurement and use outside of registered clinical trials carries regulatory and unknown health risks.
References
Research disclaimer. CompoundProfile publishes summaries of available scientific literature for educational purposes only. This page does not constitute medical advice and should not be interpreted as an endorsement of Retatrutide for any therapeutic use. Consult a licensed healthcare professional before considering any research compound. All evidence gradings reflect the state of published literature as of August 2026 and are assessed independently by ICPS.
Community Commentary
Selected discussion from r/Peptides · Curated for signal, not volume
The glucagon receptor piece is the genuinely novel thing here and I'm not sure enough people are focused on it. Every GLP-1 drug basically restricts calories through appetite — the metabolic rate problem is largely unaddressed, which is why people plateau and regain on discontinuation. Adding GCGR agonism to the stack is an attempt to fight the adaptive thermogenesis problem from the other side. Whether you can balance that against glucagon's glucose-raising effects at clinically useful doses was the real Phase II question, and the answer appears to be yes — at least over 48 weeks at the doses tested.
Exactly right. The Phase II glycaemia data showed HbA1c improvement despite GCGR agonism, which means the GLP-1R suppression of glucagon secretion is winning the net balance. What I'd want to see in Phase III is what happens over 2+ years — does that balance hold, does the liver adapt, and what happens to bone turnover markers given glucagon's known effects on osteoclast activity. The 48-week window is genuinely too short to answer these.
The 24.2% figure is remarkable in clinical context. For perspective, bariatric surgery (Roux-en-Y gastric bypass) produces roughly 25–30% total body weight loss in the first year, long considered the ceiling for obesity intervention. A weekly injection approaching that range over 48 weeks changes the clinical calculus significantly. That said — discontinuation studies matter. Semaglutide data shows most weight returns after stopping. Whether the GCGR component confers any durability advantage is the most important unanswered question for this compound.
Important to flag for anyone reading: the research market is already flooded with vendors selling "Retatrutide" vials. Given the molecular complexity — 36 amino acids, a fatty acid conjugate at Lys17 — synthesis fidelity is non-trivial to verify without LC-MS/MS and proper sequencing. The vials circulating in peptide communities have essentially zero verified purity data. The compound you're injecting when you buy this from a research vendor bears unknown relationship to what was used in the Jastreboff trial. This is a much more complex molecule than BPC-157 or semaglutide and the synthesis quality gap is larger.
Confirmed. The C18 fatty di-acid conjugation at Lys17 is particularly difficult to verify without mass spectrometry. Most research vendors do not publish sequencing or fatty acid conjugation data. A peptide that's synthesised correctly but lacks or has incorrect lipidation will have a dramatically different pharmacokinetic profile — likely a half-life measured in hours rather than days, with completely different dosing implications.
The liver steatosis angle is underappreciated in most coverage of this compound. MASLD (formerly NAFLD) affects roughly 30% of adults globally and has very limited approved pharmacotherapy. The GCGR component drives hepatic fat oxidation through a mechanism independent of body weight reduction — meaning there could be a direct liver-protective effect beyond what you'd expect purely from caloric restriction and weight loss. If TRIUMPH Phase III includes liver biopsy or MRI-PDFF endpoints (and the indications are that it does), this could be as significant as the obesity data.