Retatrutide

Retatrutide (LY3437943) is an investigational triple hormone receptor agonist that simultaneously activates GLP-1, GIP (glucose-dependent insulinotropic polypeptide), and glucagon receptors, combining the complementary metabolic actions of all three pathways in a single weekly injection. The GLP-1 component drives satiety and insulin secretion, GIP enhances adipose lipid metabolism and further modulates appetite, and glucagon-receptor activation increases energy expenditure and hepatic fat oxidation — together producing greater weight loss than single or dual agonists in the same class. In Phase 2 (New England Journal of Medicine, 2023) retatrutide produced dose-dependent weight loss of up to 24.2% of body weight at 48 weeks. Pivotal Phase 3 results have since gone further; as of July 2026 Eli Lilly reports five positive Phase 3 studies. In TRIUMPH-1 (Eli Lilly, May 2026; n=2,339, 80 weeks) the 12 mg dose produced mean weight loss of up to 28.3% (efficacy estimand; 25.0% on the treatment-regimen estimand), with 45.3% of participants losing at least 30% of body weight and a mean waist-circumference reduction of 24.1 cm; a 104-week extension in participants with BMI ≥35 reached approximately 30.3% (about 85 lbs). In TRIUMPH-4 (Eli Lilly, December 2025; obesity with knee osteoarthritis; n=445, 68 weeks) it delivered 28.7% weight loss (71.2 lbs) alongside a 75.8% reduction in WOMAC knee-pain scores, with about 1 in 8 participants (12.0% at 12 mg) free of knee pain versus 4.2% on placebo. In TRIUMPH-2 (Eli Lilly, July 2026; n=1,152, 80 weeks; obesity or overweight with type 2 diabetes) the 12 mg dose reduced body weight by 20.8% (efficacy estimand; 49.6 lbs) and HbA1c by 1.5%, versus 4.0% and 0.2% on placebo, and the 9 mg dose reduced body weight by 19.1% (45.4 lbs) and HbA1c by 1.6%. In TRIUMPH-3 (Eli Lilly, July 2026; n=1,949, 80 weeks; severe obesity, BMI ≥35, with established cardiovascular disease) the 12 mg dose reduced body weight by 22.6% (55.8 lbs) and the 9 mg dose by 21.6% (52.7 lbs), versus 3.2% on placebo (efficacy estimand), with accompanying reductions in triglycerides (37.0%), non-HDL cholesterol (16.5%), systolic blood pressure (9.3 mmHg), waist circumference (19.0 cm) and high-sensitivity C-reactive protein (51.2%). Weight loss in these two trials is lower than in TRIUMPH-1 because the populations differ: participants with type 2 diabetes, and participants with established cardiovascular disease, consistently lose less weight on incretin therapies than participants with obesity alone. In type 2 diabetes (TRANSCEND-T2D-1; Eli Lilly, March 2026; n=537, 40 weeks; published in The Lancet, 2026) the 12 mg dose reduced body weight by up to 16.8% (efficacy estimand; 15.3% on the treatment-regimen estimand) and lowered HbA1c by approximately 1.9% from a 7.9% baseline, versus 0.8% on placebo. A Phase 2a substudy (Nature Medicine, 2024; n=98) reported normalization of liver fat to below 5% in about 86% of participants at 12 mg by 24 weeks (93% by 48 weeks), supporting a MASLD/MASH signal. Across the Phase 3 program the most common adverse events were gastrointestinal (nausea, diarrhea, vomiting), consistent with the GLP-1 class. A dose-related dysesthesia signal (abnormal skin sensations), attributed to glucagon-receptor activation, was observed across trials — about 12.5% at 12 mg in TRIUMPH-1, 20.9% in TRIUMPH-4, 7.3% in TRIUMPH-2 and 6.4% in TRIUMPH-3 — generally mild-to-moderate and mostly resolving during treatment. Discontinuation due to adverse events at the 12 mg dose was 7.7% in TRIUMPH-2 and 13.5% in TRIUMPH-3, against 4.9% and 4.8% on placebo respectively. TRIUMPH-3, conducted in participants with established cardiovascular disease, produced the program's first in-study cardiovascular event data: five-component MACE occurred in 44 retatrutide participants versus 52 on placebo (hazard ratio 0.82, 95% CI 0.55–1.22), and three-component MACE in 27 versus 23 (hazard ratio 1.12, 95% CI 0.64–1.96). Both confidence intervals cross 1.0 and the trial was not powered for cardiovascular outcomes, so these figures establish neither benefit nor harm; dedicated long-term cardiovascular outcomes remain under evaluation in a separate trial expected in 2027. Retatrutide has not received FDA approval; it remains under Phase 3 registrational evaluation across obesity, type 2 diabetes, knee osteoarthritis, and obstructive sleep apnea. Following the TRIUMPH-2 and TRIUMPH-3 results, Lilly has stated it plans to submit a Biologics License Application to the FDA in the first quarter of 2027. Retatrutide cost and access As of mid-2026, retatrutide has not received FDA approval and is not commercially available as a branded pharmaceutical. It is in late-stage (Phase 3) clinical development through Eli Lilly. Retatrutide is not FDA-approved and is not lawfully available for human use in the United States. FDA states that retatrutide cannot be used in compounding under federal law — it is not eligible for the 503A or 503B compounding exemptions, and FDA has issued warning letters to telehealth companies, API distributors and outsourcing facilities involved in supplying it. The only lawful route of human exposure in the US is enrolment in an authorised clinical trial. Peptide sold by research-chemical vendors is labelled for laboratory use only and is not a legal human-use supply channel. Cost per month of research-grade retatrutide from vendors varies considerably by quantity and formulation. Branded pharmaceutical pricing will be established at approval; given tirzepatide's pricing trajectory and the triple-agonist mechanism, analyst forecasts suggest a premium pricing position relative to existing GLP-1 agonists. Retatrutide vs survodutide: Survodutide (BI 456906, Boehringer Ingelheim + Zealand Pharma) is a dual GLP-1 and glucagon receptor agonist in Phase 3 development for MASH and obesity. Compared to retatrutide, survodutide lacks the GIP receptor component; retatrutide's triple agonism adds GIP-mediated adipose lipid oxidation to the GLP-1 + glucagon combination. In trial comparisons, both compounds show substantial weight reductions (retatrutide 24.2% at 12 mg/week in Phase 2; survodutide 18.7% at highest dose in Phase 2). Neither compound has a direct head-to-head trial yet. Both represent the next tier beyond tirzepatide in the GLP-1 + additional agonism category. Retatrutide's MASH indication (liver fat reduction) also overlaps with survodutide's primary development focus. The competitive landscape in this category is evolving rapidly as multiple Phase 3 readouts are expected through 2026–2027.