# Retatrutide: Pharmacokinetics and Trial Evidence — Medicine Retatrutide > Retatrutide (LY3437943) — Phase 2 trial data, ~6-day half-life, triple-agonist mechanism, and safety profile. An apothecary's record of the published clinical literature. A pharmacopeia-register digest of the LY3437943 research record — half-life, mechanism, Phase 2 weight loss, and safety, cited to source. ## In plain terms Retatrutide is an investigational drug being tested in large clinical trials for obesity and type 2 diabetes. It is not approved by the FDA or any other regulator — it is not available as a prescription medicine and cannot be legally obtained through a pharmacy. Trials are still running. What makes it distinct from earlier weight-loss drugs is its mechanism: retatrutide activates three hormonal signals at once — GLP-1 (which curbs appetite), GIP (which helps insulin work), and glucagon (which boosts calorie burning). That triple action appears to explain why Phase 2 trial participants lost roughly 24% of body weight over 48 weeks — more than previous drugs in this class have achieved. The main side effects seen in trials are nausea, vomiting, and a dose-related rise in heart rate. The drug has an approximately 6-day half-life, which is why it is dosed once a week. Long-term cardiovascular and kidney safety is still being measured in ongoing Phase 3 trials. This site summarizes the published literature on retatrutide — the pharmacokinetics, the trial results, and the safety data. What people report from research-use communities is on [the effects page](/effects), clearly labeled as anecdotal. ## What the Phase 2 trials measured Retatrutide (LY3437943), a 39-amino-acid synthetic peptide, is a simultaneous agonist (activator) at three hormone receptors: GIP (glucose-dependent insulinotropic polypeptide), GLP-1 (glucagon-like peptide-1), and glucagon. This triple action is the basis of its weight-loss and metabolic effects. In the 48-week Phase 2 obesity trial (Jastreboff et al., *New England Journal of Medicine*, 2023), once-weekly subcutaneous retatrutide at 12 mg produced a mean body-weight reduction of 24.2% versus 2.1% in the placebo group [1]. The 338 adult participants had a BMI of ≥30, or ≥27 with a weight-related comorbidity. In a parallel Phase 2 trial in type 2 diabetes (Rosenstock et al., *Lancet*, 2023), retatrutide 12 mg lowered HbA1c (glycated hemoglobin — a measure of average blood glucose) by 2.02 percentage points at 24 weeks and reduced body weight by 16.94% at 36 weeks, versus changes of 0.01% and 3.00% with placebo [2]. The first-in-human Phase 1b study (Urva et al., *Lancet*, 2022) established a plasma half-life of approximately 6 days, consistent with once-weekly subcutaneous dosing [4]. The highest-dose group lost 8.96 kg placebo-adjusted over 12 weeks. A 2025 systematic review of 53 phase 2 and 3 obesity trials confirmed retatrutide in active Phase 3 (the TRIUMPH program); the incretin category shows phase 2 weight-loss ranges of 7.4% to 24.2% across agents [11]. ## What does retatrutide do Retatrutide engages three class-B G protein-coupled receptors (GPCRs — cell-surface proteins that relay hormonal signals into the cell) simultaneously. The GLP-1 arm suppresses appetite and slows gastric emptying. The GIP arm enhances glucose-dependent insulin secretion and influences fat-tissue metabolism. The glucagon arm increases energy expenditure and hepatic (liver) lipid breakdown — the mechanism believed to account for the larger weight loss relative to single or dual agonists [6]. Cryo-EM structural studies (Li et al., *Cell Discovery*, 2024) resolved retatrutide's binding at all three receptor complexes, showing it is approximately 8.9× more potent at GIPR than native GIP but 0.3–0.4× as potent at GCGR/GLP-1R compared with the endogenous hormones [3]. The balanced potency profile explains why the glucagon arm adds metabolic burn without producing the hyperglycemia that unbalanced glucagon activation would cause. A 2025 review (Katsi et al., *Biomolecules*) characterized the up-to ~24% weight loss as a step-change in incretin pharmacology, attributing the additional effect to the glucagon receptor's contribution to energy expenditure [6]. ## Retatrutide results: liver and metabolic endpoints Beyond weight and glucose, the Phase 2 program included a substudy in metabolic dysfunction-associated steatotic liver disease (MASLD — formerly NAFLD — a condition in which excess fat accumulates in the liver due to metabolic risk factors). In 98 participants with ≥10% liver fat measured by MRI-PDFF (a non-invasive liver-fat measurement), retatrutide 12 mg reduced liver fat by 82.4% at 24 weeks versus a 0.3% change with placebo [5]. By 48 weeks the reduction was 86.0% at 12 mg. Eighty-six percent of 12-mg participants reached a normal liver-fat level (below 5%) at 24 weeks [5]. A 2025 review of multifunctional incretin peptides noted emerging evidence that incretin-based therapies as a class show signals of benefit across fatty liver, chronic inflammation, sleep apnea, and possibly bone and cognitive outcomes — with retatrutide cited among agents in development within this expanding comorbidity landscape [10]. Investigational status stands. All retatrutide efficacy figures are from controlled trials. The TRIUMPH Phase 3 program and dedicated cardiovascular and kidney outcomes trials are ongoing as of mid-2026 [11]. ## Is retatrutide fda approved Retatrutide is not approved by the FDA or any regulatory authority as of 2026. It is investigational. It cannot be prescribed, dispensed, or lawfully sold as a medicine. The compound is being studied under Eli Lilly's TRIUMPH Phase 3 program, which includes trials in obesity, type 2 diabetes, cardiovascular outcomes, and chronic kidney disease. The FDA has not issued approval for any indication. The search term 'GLP-3' is sometimes used to describe retatrutide — this is a misnomer. There is no GLP-3 receptor. Retatrutide is a triple agonist acting on the GIP receptor, the GLP-1 receptor, and the glucagon receptor. For [Retatrutide research](/research) data by endpoint, see the research page. For pharmacokinetics and dosing protocol information from trials, see the [retatrutide half life](/half-life) page. --- An apothecary's specimen record of the retatrutide pharmacokinetics literature — trial findings documented to source, no dispensary behind the cabinet, no prescription filled here.