# Retatrutide: What the Phase 2 and Phase 3 Trials Have Actually Found > Retatrutide (LY3437943) is an investigational triple agonist in Eli Lilly's Phase 3 TRIUMPH program. A plain-spoken reading of the published clinical evidence — what the trials studied, what they found, and what remains open. A plain-spoken reading of the retatrutide trials — what the studies actually found, and what they don't yet show. Every quantitative claim cited to source. ## Start here: what retatrutide is and what the trials have studied Retatrutide is an investigational drug — meaning it is still in clinical trials and has not been approved by the FDA or any other regulator. It is being studied by Eli Lilly under the development code LY3437943 as a possible treatment for obesity, type 2 diabetes, and related conditions. The compound works by activating three hormone receptors at the same time: GLP-1 (glucagon-like peptide-1, a gut hormone that reduces appetite and improves blood-sugar control), GIP (glucose-dependent insulinotropic polypeptide, another gut hormone that amplifies insulin release), and glucagon (a pancreatic hormone that increases calorie-burning). That three-way activation is where the "triple agonist" label comes from. Phase 2 trials — mid-stage human trials designed to test whether a drug works at all before the larger Phase 3 confirmation studies — showed weight reductions considerably larger than earlier single- or dual-receptor drugs. A 48-week Phase 2 obesity trial found a mean body-weight change of -24.2% at the highest dose versus -2.1% with placebo [1]. That is the headline finding, and it explains why retatrutide has attracted wide attention. But it is not approved, not available by prescription, and not a finished product. This site summarizes what the published studies have measured — the benefits, the side effects, the open questions — and nothing more. What people report from research-use communities — including the downsides — is on [the effects page](/effects). Phase 3 trials (the large, definitive confirmation studies) are ongoing under the TRIUMPH program. Results are expected in 2026-2027. Until those complete and a regulatory submission is made and reviewed, retatrutide remains investigational. ## What does retatrutide do Retatrutide acts on three receptors simultaneously — a design that allows each receptor arm to contribute differently to the overall metabolic effect. The GLP-1 receptor arm suppresses appetite and slows gastric emptying (the rate at which food leaves the stomach), reducing caloric intake. The GIP receptor arm amplifies insulin secretion after eating and appears to support fat-tissue metabolism. The glucagon receptor arm raises energy expenditure — the number of calories the body burns at rest — and promotes breakdown of fat in the liver. In clinical terms, the compound produced the following in Phase 2 trials: mean body-weight reduction of -24.2% at 48 weeks in a 338-person obesity study [1]; HbA1c (glycated hemoglobin — a marker of average blood-sugar control over three months) reduction of -2.02% at 24 weeks in a 281-person type 2 diabetes study [2]; liver-fat reduction of -82.4% at 24 weeks in participants with MASLD (metabolic dysfunction-associated steatotic liver disease, the current term for fatty liver linked to metabolic risk factors) [5]; and UACR (urine albumin-to-creatinine ratio, a marker of kidney-filter leakage) reduction of ~37% in type 2 diabetes participants [7]. A 2025 narrative review in Biomolecules characterizes the up-to ~24% weight loss as a step-change versus earlier incretin-class compounds [6]. None of these are claims about what the compound will do for any individual. They are what the trials measured in the populations they enrolled. ## Is retatrutide fda approved No. Retatrutide is not FDA-approved as of 2026. It is an investigational drug in Phase 3 clinical trials. Phase 3 data need to be collected, analyzed, and submitted to the FDA before any approval review can take place. The Phase 3 TRIUMPH program (covering obesity, type 2 diabetes, cardiovascular outcomes, chronic kidney disease, and an active-comparator study against tirzepatide) is ongoing. Approval is not guaranteed; most investigational drugs do not reach market. This site does not track regulatory timelines and makes no prediction about approval. The gap between the Phase 2 results and approval matters: Phase 2 trials are not designed to establish long-term safety, cardiovascular outcomes, or durability off treatment. Those are Phase 3 questions. The literature on analogous GLP-1-class agents suggests substantial weight regain after discontinuation — an open question for retatrutide that the TRIUMPH program is designed in part to address. ## What retatrutide research has measured — and what remains open The strongest signals from the published literature are weight reduction, blood-glucose improvement, liver-fat reduction, and a favorable early kidney-marker profile. A 2025 meta-analysis pooling three RCTs (878 participants) found a mean weight difference of -14.33% versus placebo, with no statistically significant difference in overall adverse event rates between retatrutide and placebo (RR 1.11, P=0.24) [8]. A review in Cell (2024) places triple agonism as the pharmacological basis for weight losses of up to ~20-30%, rivaling bariatric surgery outcomes [9]. The safety picture is real and must be read clearly: gastrointestinal adverse events — nausea, vomiting, diarrhea, constipation — were the most common adverse effects in Phase 2 and were dose-related. A dose-dependent increase in resting heart rate (mean ~5-7 bpm at the highest doses, peaking around week 24) was documented. These are trial findings in closely monitored populations. A dedicated cardiovascular outcomes trial is ongoing. Long-term durability and off-treatment weight regain remain unstudied for retatrutide specifically. [Retatrutide research](/research) page covers the mechanism and key trial findings in detail. [Retatrutide effects](/effects) covers the human-layer signals and safety cautions fully. ## Retatrutide availability Retatrutide is not available as an approved prescription product anywhere in the world as of 2026. It is accessible only to participants enrolled in clinical trials. A gray market exists for research-labeled retatrutide — unregulated material sold under that name through peptide research channels — but such material carries no verified identity, purity, or sterility, and obtaining it is outside any clinical oversight structure. This site does not sell, link to, or endorse any source of retatrutide. The [Retatrutide references](/references) page lists the published literature used throughout this digest. --- A plain-spoken reading of the retatrutide trial record — what Phase 2 measured, what Phase 3 is designed to determine, and what remains genuinely open; not a clinic, not a pharmacy, not a vendor.