# Retatrutide: What the Liver-Fat and Obesity Trials Actually Measured > Retatrutide produced -24.2% body-weight change and -82.4% liver fat reduction in Phase 2 trials. An investigative digest of the published record — what was measured, how, and what remains unknown. A forensic reading of the published record on an investigational triple agonist — the numbers, the mechanisms, and the open questions. What the trials measured is documented here. What remains unknown is documented too. ## The short version Retatrutide is an investigational drug — not yet approved anywhere — being developed by Eli Lilly. It works by activating three hormone receptors at once: GLP-1 (which cuts appetite and slows gastric emptying), GIP (which boosts insulin response and affects fat tissue), and glucagon (which increases energy burn and speeds liver-fat metabolism). That combination is why the trial numbers look the way they do. In a 48-week Phase 2 trial in people with obesity, the highest dose studied produced an average 24.2% reduction in body weight. In a separate substudy focused on people with fatty liver disease (called MASLD — metabolic dysfunction-associated steatotic liver disease), the same dose reduced liver fat by 82.4% at 24 weeks, with 86% of participants reaching normal liver-fat levels. It is not available as a prescription. It is not at a pharmacy. It is in Phase 3 clinical trials as of 2026 — the TRIUMPH program — and no regulator has approved it yet. What people report using research-labeled material, and what to be cautious about, is on the [Retatrutide effects](/effects) page. This site documents the published record. Nothing more. ## What the retatrutide trials measured Retatrutide (LY3437943) is a synthetic 39-amino-acid peptide engineered to act simultaneously at three class-B G-protein-coupled receptors: the GLP-1 receptor (GLP-1R), the glucose-dependent insulinotropic polypeptide receptor (GIPR), and the glucagon receptor (GCGR). No approved drug hits all three at once. The triple-receptor mechanism is the specific innovation under investigation. The Phase 2 obesity trial enrolled 338 adults with a BMI of 30 or higher — or 27 to <30 with a weight-related comorbidity. Participants received once-weekly subcutaneous injections at 1, 4, 8, or 12 mg, or placebo, for 48 weeks. At the 12 mg dose, mean body-weight change was -24.2% versus -2.1% with placebo [1]. The dose-response was clear across all four active arms. The Phase 2 type 2 diabetes trial enrolled 281 adults. At 12 mg over 36 weeks, HbA1c (glycated hemoglobin — a blood marker that tracks average glucose over three months) fell by 2.02 percentage points versus a 0.01 point change with placebo, and body weight fell 16.94% versus 3.00% with placebo [2]. No severe hypoglycemia and no deaths were recorded in the trial. The MASLD substudy is where retatrutide's liver-fat effect is most clearly documented. Ninety-eight participants with obesity and MASLD — all with liver fat of at least 10% on MRI-PDFF (magnetic resonance imaging proton density fat fraction, a precise non-invasive measure of liver fat) — were followed over 48 weeks. Relative liver-fat reduction at 24 weeks was -42.9%, -57.0%, -81.4%, and -82.4% at the 1, 4, 8, and 12 mg doses versus +0.3% with placebo. At 48 weeks, the 12 mg group showed -86.0% [5]. These are the largest measured liver-fat reductions published for any single pharmacological agent to date in a Phase 2 trial — a systematic review confirmed the 81% placebo-subtracted MRI-PDFF reduction was the highest among agents reviewed, versus 41% for semaglutide and 47% for tirzepatide [7]. The first-in-human Phase 1b study, in 72 adults with type 2 diabetes, established the pharmacokinetic profile: half-life approximately 6 days, consistent with once-weekly dosing. The highest-dose group lost 8.96 kg placebo-adjusted over 12 weeks [4]. These are study-design measurements in controlled trials, not prescriptions or instructions. For [Retatrutide research](/research) in full, including the recent 2024-2025 publications, see the research page. For what those numbers mean and what remains uncertain, read on. ## What does retatrutide do Retatrutide does three mechanistic things simultaneously that prior single or dual agents did not. The GLP-1 receptor arm suppresses appetite via central nervous system signaling and slows gastric emptying, reducing caloric intake. The GIPR arm augments glucose-dependent insulin secretion and modulates adipose tissue metabolism. The glucagon receptor arm — the addition that distinguishes retatrutide from dual GLP-1/GIP agonists — activates energy expenditure pathways and accelerates hepatic lipid metabolism via cAMP/PKA (cyclic adenosine monophosphate/protein kinase A) signaling. The three arms together appear to produce larger weight and liver-fat effects than any single-arm or dual-arm approach in the trials reviewed. A 2025 review synthesized the Phase 1 and 2 data and characterized retatrutide's up-to-24% weight loss as a step-change versus prior incretin therapies [6]. Cryo-EM (a high-resolution imaging technique for visualizing molecular structures) confirmed retatrutide engages all three receptors simultaneously. Relative potency at the GIPR is 8.9 times that of native GIP, while at the glucagon receptor and GLP-1R it is 0.3 and 0.4 times native hormone potency, respectively [3]. The engineered bias toward GIP and the attenuated glucagon activation is the deliberate design: enough glucagon effect for metabolic and liver-fat benefit, not so much as to raise glucose. For a full mechanistic reading, see [how does retatrutide work](/how-it-works). ## Is retatrutide fda approved Retatrutide is not FDA-approved. It is not approved by any regulatory agency as of mid-2026. It is an investigational new drug in Phase 3 clinical trials under Eli Lilly's TRIUMPH program, which is studying obesity, type 2 diabetes, and cardiovascular and kidney outcomes. No new drug application has been filed or accepted. The Phase 2 data are published and publicly available. The Phase 3 trials are ongoing. Whether and when the FDA acts on a regulatory submission depends on Eli Lilly's filing timeline and Phase 3 results, neither of which is fixed as of this writing. This distinction matters. Semaglutide and tirzepatide are approved drugs with labeled indications and pharmacist-dispensed formulations. Retatrutide is not. Any retatrutide-labeled material available outside a clinical trial is unregulated, unverified, and outside any clinical oversight structure. ## Retatrutide availability Retatrutide is not commercially available as a prescription drug. The only legitimate access is enrollment in an active clinical trial. Phase 3 trials are ongoing under the NCT registry (the TRIUMPH series, plus dedicated cardiovascular and kidney outcome trials NCT06383390, NCT05929066, NCT05931367, and NCT05882045). A gray market exists for research-labeled retatrutide. The FDA issued more than 50 warning letters to vendors in 2025 citing violations of the Federal Food, Drug, and Cosmetic Act. Research-labeled material is unregulated: purity, identity, and sterility are unverified, and there is no clinical oversight of its use. This site does not sell, source, or direct readers toward any such product. ## When will retatrutide be available There is no announced approval date. Eli Lilly's Phase 3 TRIUMPH program is ongoing as of mid-2026. If Phase 3 results support regulatory submission and the FDA accepts a new drug application, the typical review timeline from submission to decision is 10 to 12 months for standard review. No submission has been publicly announced as of this writing. Speculative timelines circulating in community forums are not based on confirmed Eli Lilly filing schedules. --- A forensic reading of the published retatrutide record — trial numbers logged to source, safety signals named, and nothing here dispensed, prescribed, or sold.