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Retatrutide: quick citable summary
Retatrutide is listed by PeptaHub as a weight loss peptide with a research only legal-status classification. The page summarizes mechanism, research context, common routes, safety notes, and references for writers and AI answer engines.
PeptaHub. “Retatrutide: Mechanism, Research Context, Safety.” peptahub.com, 2026. https://peptahub.com/peptides/retatrutide. Licensed CC BY 4.0.
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What is Retatrutide?
Retatrutide is the investigational triple-agonist in the GLP-1 cluster. It targets GLP-1, GIP, and glucagon receptors, which may explain the large trial weight-loss signal. It is not FDA-approved, has no consumer access pathway, and should be compared as research only.[4]
GLP-1 comparison
Educational only. This comparison is not medical advice, does not recommend any medication, and separates FDA-approved prescription drugs from investigational compounds and fast-changing compounding rules.
| Agent | Brand terms | Mechanism | Regulatory angle | Evidence note |
|---|---|---|---|---|
| Semaglutide | Ozempic / Wegovy / Rybelsus | GLP-1 receptor agonist | FDA-approved prescription drug for type 2 diabetes, chronic weight management, and selected cardiovascular-risk indications by product label. | Deepest outcomes dataset in the cluster: STEP, SUSTAIN, SELECT, FLOW, and PIONEER programs. |
| Tirzepatide | Mounjaro / Zepbound | Dual GIP / GLP-1 receptor agonist | FDA-approved prescription drug for type 2 diabetes, chronic weight management, and obstructive sleep apnea in adults with obesity by product label. | SURPASS and SURMOUNT trials show greater average weight loss than semaglutide in head-to-head and cross-trial contexts. |
| Retatrutide | LY3437943, no approved brand | Triple GIP / GLP-1 / glucagon receptor agonist | Investigational only. Not FDA-approved and not legally available outside clinical trials or regulator-authorized access pathways. | Phase 2 and emerging Phase 3 data are high-interest but still lack approval, label review, and long-term post-market safety data. |
| Orforglipron | Foundayo | Oral small-molecule GLP-1 receptor agonist | FDA-approved prescription drug for chronic weight management in eligible adults; diabetes status requires current-label confirmation. | ATTAIN trials support the oral GLP-1 pill frame: no injection and no food or water restrictions, with less outcomes history than injectable semaglutide. |
Overview
Retatrutide (LY3437943) is Eli Lilly's investigational triple hormone receptor agonist targeting GLP-1, GIP, and glucagon receptors simultaneously. In the Phase 3 TRIUMPH-1 trial reported in 2026, the 12 mg dose produced 28.3% mean weight loss at 80 weeks, with about 45% of participants reaching at least 30% weight loss — among the largest body weight reductions reported for a pharmacological obesity treatment to date.
Mechanism of action
Retatrutide activates three complementary hormone receptors in a single molecule. GLP-1 receptor agonism slows gastric emptying, suppresses appetite via hypothalamic satiety pathways, and stimulates glucose-dependent insulin secretion. GIP receptor agonism potentiates GLP-1-driven insulin release, improves beta-cell function, and may reduce GLP-1-associated nausea. Glucagon receptor agonism increases hepatic glucose output and stimulates thermogenesis — effects that would raise blood glucose in isolation but are counterbalanced by the insulinotropic GLP-1/GIP axes. The net metabolic result is pronounced energy deficit, enhanced fat oxidation, and superior weight loss versus dual-agonists. A C18 fatty acid chain binds reversibly to serum albumin, extending the half-life to ~6 days and enabling once-weekly subcutaneous dosing.
Reported study ranges
| Purpose | Route | Reported range | Frequency | Notes |
|---|---|---|---|---|
| obesity / weight loss (clinical trial protocol) | subcutaneous | 2–12 mg | once weekly | Phase 3 protocols titrated from 2 mg weekly, increasing every 4 weeks to target doses of 8 mg or 12 mg. Slower titration reduces GI side effects. |
| type 2 diabetes management (clinical trial protocol) | subcutaneous | 4–8 mg | once weekly | Clinical trial data at 4–8 mg weekly showed A1C reductions up to 2.0%. Titration from 2 mg weekly over 12–16 weeks. |
Reported ranges are for research context only. Consult a qualified healthcare professional before using any peptide.
Convert Retatrutide research-range units
Need to convert mg to mcg, dose volume, or U-100 syringe units? The Retatrutide dose calculator is preloaded with these ranges, or use the general dose unit converter.
Research summary
Phase 3 TRIUMPH-1 topline results reported in May 2026 showed retatrutide 12 mg produced 28.3% mean weight loss at 80 weeks, with 45.3% of participants reaching at least 30% weight loss. Earlier Phase 2 data (NEJM, 2023) showed 24.2% mean weight reduction at 48 weeks with 12 mg weekly dosing. TRIUMPH-4 (participants with overweight/obesity and knee osteoarthritis) reported 26.4–28.7% mean weight loss depending on dose. TRANSCEND-T2D-1 met primary and secondary endpoints for A1C reduction and weight loss in type 2 diabetes. Retatrutide remains investigational and is not FDA-approved as of mid-2026; NDA submission for obesity is expected Q4 2026, with approval projected no earlier than late 2027.[1][2][3][4][5]
Evidence grading
Each claimed benefit is graded by the strength of available evidence. Grades reflect study quality, not effect size.
Strong = multiple RCTs · Moderate = limited trials or observational · Preliminary = animal or in vitro only · Insufficient = anecdotal or no published data
Side effects
Side effects vary by individual. This is not an exhaustive list. Report unusual symptoms to a healthcare professional.
Common stacks
Peptides commonly paired with Retatrutide for synergistic effects.
Legal status
Retatrutide is an investigational drug (IND) under active Phase 3 development by Eli Lilly. It is not FDA-approved and not legally available outside clinical trials in the US. Research chemical suppliers offer compounded or synthesized versions without regulatory oversight; quality and safety cannot be verified.
Sourcing & access
Research compound
Retatrutide is classified as a research compound. Regulatory status varies by jurisdiction. Always verify current legal status and source from vendors providing third-party certificates of analysis (COA).
Frequently asked questions
Retatrutide (LY3437943) is Eli Lilly's investigational triple hormone receptor agonist targeting GLP-1, GIP, and glucagon receptors in a single molecule. It is in Phase 3 clinical development for obesity and type 2 diabetes.
It activates three complementary hormone receptors. GLP-1 agonism suppresses appetite and slows gastric emptying, GIP agonism potentiates insulin release and may reduce nausea, and glucagon agonism increases hepatic glucose output and stimulates thermogenesis, driving a pronounced energy deficit and fat oxidation.
Phase 3 TRIUMPH-1 topline results reported in May 2026 showed 28.3% mean weight loss at 80 weeks with 12 mg weekly retatrutide, and 45.3% of participants reached at least 30% weight loss. Earlier Phase 2 data published in NEJM showed 24.2% mean weight reduction at 48 weeks. Retatrutide remains investigational and is not FDA-approved.
No. As of May 2026 retatrutide is an investigational drug under active Phase 3 development and is not FDA-approved. It is not legally available outside clinical trials in the US.
There is no established dose, because retatrutide is investigational and not approved anywhere. In the phase 2 trials, weekly subcutaneous doses were titrated from a 2 mg starting dose up to maintenance doses ranging from 0.5 mg to 12 mg, with slower titration used to reduce gastrointestinal side effects. The phase 3 TRIUMPH-1 topline reported results at 12 mg. The published TRIUMPH design paper does not specify the full phase 3 dose ladder.
Retatrutide has a half-life of approximately 6 days. A C18 fatty acid chain attached to the peptide binds reversibly to serum albumin, slowing renal clearance and extending duration of action. This albumin-binding strategy enables once-weekly subcutaneous dosing at 2 to 12 mg and produces steady plasma levels across the dosing interval.
The most common side effects are gastrointestinal and dose-dependent: nausea, vomiting, diarrhea, constipation, and decreased appetite. Injection site reactions, hypoglycemia when combined with insulin or sulfonylureas, and a GLP-1 class warning for thyroid C-cell effects have also been noted.
Research references
- Triple-Hormone-Receptor Agonist Retatrutide for Obesity — A Phase 2 TrialPubMed
- Retatrutide, a GIP, GLP-1 and glucagon receptor agonist, for people with type 2 diabetes: a randomised, double-blind, placebo and active-controlled, parallel-group, phase 2 trialPubMed
- Retatrutide for the treatment of obesity, obstructive sleep apnea and knee osteoarthritis: Rationale and design of the TRIUMPH registrational clinical trialsPubMed
- Lilly's triple agonist, retatrutide, delivered powerful weight loss in pivotal Phase 3 obesity trialSource
- Effects of once-weekly subcutaneous retatrutide on weight and metabolic markers: A systematic review and meta-analysis of randomized controlled trialsPubMed