This page has not yet been reviewed by a credentialed medical professional. It is educational and is not medical advice.
Retatrutide: key facts
Evidence level Human trials
Approved as a medicineNo
Randomized trials on PubMed8
Registered human trials33
People use it forWeight loss and type 2 diabetes. A triple GIP/GLP-1/glucagon agonist with positive phase 3 results that is not approved yet, but is widely sold online anyway.
In tested sportCheck the current WADA list
In one sentence: Retatrutide is not an approved medicine. Its strongest evidence is human trials, with 8 randomized trials listed on PubMed and 33 registered human trials.
Phase 2 and phase 3 clinical trials demonstrate up to 24% weight loss in adults with obesity and significant HbA1c reductions in type 2 diabetes. Unapproved; Lilly plans FDA submission in 2027.
What it is
Retatrutide (code name LY3437943) is an experimental synthetic peptide developed by Eli Lilly that simultaneously activates three metabolic hormone receptors: glucose-dependent insulinotropic polypeptide (GIP), glucagon-like peptide-1 (GLP-1), and glucagon. It is currently in phase 3 clinical trials (the TRIUMPH program) for chronic weight management, type 2 diabetes, and metabolic dysfunction-associated steatohepatitis (MASH). It is not approved by any drug regulator, but unauthorized "research" versions are widely sold online.
How it is thought to work
Retatrutide is a triple agonist engineered with balanced potency across all three incretin and metabolic pathways. GLP-1 and GIP receptor agonism stimulate glucose-dependent insulin secretion, suppress inappropriate glucagon release at elevated blood glucose levels, delay gastric emptying, and act on hypothalamic satiety circuits to curb appetite. Glucagon receptor agonism increases resting energy expenditure and stimulates hepatic lipid breakdown (lipolysis and fatty acid oxidation). This synergy produces both substantial weight loss and rapid clearance of liver fat.
What the studies found5 studies explained
In a landmark 48-week phase 2 randomized controlled trial published in The New England Journal of Medicine (338 adults with obesity), retatrutide produced dose-dependent weight loss reaching an average of 24.2% at the 12 mg dose, with 100% of participants on that dose achieving at least 5% weight loss. In a phase 2 MASLD substudy published in Nature Medicine, retatrutide reduced liver fat by 82% to 86% relative to baseline, normalizing liver fat in over 85% of patients. Phase 3 results from the TRANSCEND-T2D-1 trial (537 adults with type 2 diabetes) published in The Lancet in 2026 confirmed robust HbA1c reductions (up to 2.0%) alongside 12.0% weight reduction.
338 adults with BMI >= 30 or BMI 27 to < 30 with at least one weight-related condition
What they found
At 48 weeks, retatrutide produced mean weight reductions of -8.7% at 1 mg, -17.1% at 4 mg, -22.8% at 8 mg, and -24.2% at 12 mg, compared to -2.1% with placebo. A weight reduction of >= 5% was achieved by 100% of participants on 8 mg and 12 mg.
Limitations
Phase 2 trial with limited sample size and 48-week duration. Long-term efficacy, cardiovascular outcomes, and weight regain after discontinuation require larger Phase 3 confirmation.
Bajaj HS, Welch M, Shah P · Lancet · 2026 · PMID 42250575
humanRandomized, double-blind, active- and placebo-controlled phase 3 trial (TRANSCEND-T2D-1)
Who / how many
537 adults with type 2 diabetes inadequately controlled on diet and exercise or metformin
What they found
At week 40, retatrutide significantly lowered HbA1c (by up to 2.0%) and body weight (by up to 12.0%), outperforming both placebo and dulaglutide comparator arms with a consistent safety profile.
Limitations
Conducted specifically in individuals with type 2 diabetes; primary evaluation endpoint was 40 weeks, and multi-year cardiovascular durability data are still accumulating.
98 adults with obesity and metabolic dysfunction-associated steatotic liver disease (MASLD; liver fat >= 8%)
What they found
Retatrutide (8 mg and 12 mg) reduced liver fat content by 82% to 86% relative to baseline at 24 and 48 weeks measured by MRI-PDFF, with >85% of patients achieving normal liver fat (<5%).
Limitations
Secondary substudy of 98 patients; assessed liver fat non-invasively via MRI proton density fat fraction rather than paired liver biopsy histology.
humanRandomized, double-blind, active- and placebo-controlled phase 2 trial
Who / how many
281 adults with type 2 diabetes
What they found
At 36 weeks, retatrutide dose-dependently reduced HbA1c by up to 2.02% and body weight by up to 16.94 kg (17.2%), with glycemic improvements superior to dulaglutide 1.5 mg.
Limitations
36-week treatment duration; active comparator was dulaglutide rather than higher-dose tirzepatide or semaglutide.
humanRandomized, double-blind body composition substudy (DXA)
Who / how many
87 adults with type 2 diabetes from the phase 2 trial
What they found
Dual-energy X-ray absorptiometry demonstrated marked reductions in total fat mass and visceral adipose tissue with preservation of the proportion of lean mass relative to total weight.
Limitations
Substudy of 87 participants; DXA assesses body compartments by density and cannot distinguish muscle water content from contractile protein.
33 trials on ClinicalTrials.gov list Retatrutide as an intervention; the most advanced are shown. Registration is not evidence of benefit: many trials are ongoing, unpublished or never reported results.
Data pulled from the ClinicalTrials.gov API. Check sponsors: several newer peptide registrations come from companies that also sell the product.
European research
182 records in Europe PMC mention Retatrutide in the title or abstract. Of the 25 most-cited with European author affiliations that we sampled, the most common countries were UK (12), Ireland (7), Italy (4), Germany (3).
Adverse events in clinical trials are predominantly gastrointestinal: nausea (affecting up to 45% on the highest dose), diarrhea, vomiting, and constipation. These are mostly mild to moderate and peak during dose titration. Trials also observed a dose-dependent, transient increase in resting heart rate (peaking around week 24 and declining thereafter) and mild cutaneous sensations (hyperesthesia or allodynia). Cardiovascular outcome trials (TRIUMPH-Outcomes) are ongoing to confirm long-term safety.
Not FDA-approved. Currently undergoing Phase 3 clinical trials (the TRIUMPH program). Eli Lilly has announced plans for an FDA filing in 2027. Selling unapproved peptides for human use is illegal under the Federal Food, Drug, and Cosmetic Act.
Canada
Not authorized by Health Canada. Health Canada issued a public advisory warning against purchasing and injecting unauthorized peptides sold online.
European Union
No marketing authorization from the European Medicines Agency (EMA). It remains an investigational product with no lawful market in the EU.
Sport (WADA)
Prohibited at all times in sport under Category S0 (Non-approved substances).
How does retatrutide compare to tirzepatide and semaglutide?
Semaglutide targets one receptor (GLP-1), tirzepatide targets two (GLP-1 and GIP), and retatrutide targets three (GLP-1, GIP, and glucagon). In Phase 2 trials, retatrutide achieved an average of 24.2% weight loss at 48 weeks, compared to roughly 15% for semaglutide and 21% for tirzepatide in their respective trials.
Is retatrutide approved by the FDA?
No. Retatrutide is an investigational drug in Phase 3 trials. Eli Lilly plans an FDA submission in 2027. Any retatrutide sold online today as a "research chemical" is unapproved and unregulated.
What is retatrutide's effect on liver fat?
In a Phase 2 trial substudy of patients with metabolic dysfunction-associated steatotic liver disease (MASLD), retatrutide reduced liver fat by 82% to 86% relative to baseline, with more than 85% of patients achieving normal liver fat levels (<5%).
