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An experimental weekly shot from Eli Lilly that acts on three hormone targets, tested for weight loss; not approved anywhere.
An investigational once-weekly triple agonist of the GIP, GLP-1 and glucagon receptors from Eli Lilly, with Phase 3 obesity results published in 2026. Not approved anywhere.
Powder: fridge (2–8 °C) for the short term, freezer (−20 °C) for the long term; after mixing, fridge for up to 28 days (general guidance, not tested for this compound).
Side effects and warnings
Common side effects are nausea, vomiting, diarrhea and constipation. They were more common at higher doses and while the dose was being raised.
Heart rate went up. In Phase 2 this peaked around week 24 and then went down.
Some people had odd or painful skin feelings: 5.1–12.5% on retatrutide versus 0.9% on placebo in TRIUMPH-1 (company-reported), and 4–7% versus 1% in the published diabetes trial.
A summary of the sources on this page, not medical advice.
Discovered by: Tamer Coskun and colleagues, Eli Lilly
Year: 2022
Developer: Eli Lilly and Company
What it is
Retatrutide is an experimental drug from the company Lilly. It is a short chain of amino acids (a peptide). It copies three body hormones at once: GIP, GLP-1 and glucagon. The first two are the same targets as the drug tirzepatide. Adding glucagon is meant to help the body burn more energy. It is also meant to clear fat from the liver. Lilly ran a large late-stage (Phase 3) weight-loss trial, published in a medical journal in September 2026. People on the highest dose lost about 25% of their body weight over 80 weeks, on average, counting everyone who started whether or not they stayed on the drug (about 28% by the company’s count, which includes only those who stayed on it).
It is not approved anywhere. It is only available inside clinical trials. Anything sold under this name outside a trial is not the product being tested.
Retatrutide (LY3437943) is a single-chain synthetic peptide derived from a GIP scaffold and lipidated with a C20 fatty diacid for albumin binding. In vitro it shows more activity at the GIP receptor than at the GLP-1 and glucagon receptors, where its activity is roughly balanced (Coskun et al., 2022). Glucagon receptor agonism is intended to increase hepatic fatty acid oxidation and energy expenditure, while GLP-1 and GIP agonism suppress appetite and blunt glucagon-driven hyperglycaemia. In obese mice, glucagon-receptor-driven increases in energy expenditure added to the intake reduction from GIP and GLP-1 agonism. Its half-life in Phase 1 was about 6 days, supporting once-weekly dosing.
Who made it and when
Lilly’s peptide team, including Tamer Coskun, first described the drug in 2022. Mid-stage (Phase 2) results came out in 2023. The late-stage (Phase 3) trials, called TRIUMPH, started that same year. The first Phase 3 results came in December 2025. Results from the main weight-loss trial came in May 2026. Results from the diabetes and heart-disease trials came in July 2026. The first two trials were published in medical journals in September 2026, and a head-to-head trial against Ozempic read out in October 2026. Lilly says it plans to ask for US approval in the first quarter of 2027.
Coskun and colleagues described the design and preclinical pharmacology in Cell Metabolism in 2022. Phase 2 obesity (n=338) and type 2 diabetes (n=281) trials read out in 2023. The TRIUMPH program comprises TRIUMPH-1 (obesity, with knee osteoarthritis and sleep apnoea sub-studies), TRIUMPH-2 (obesity with T2D), TRIUMPH-3 (severe obesity with established CVD), TRIUMPH-4 (obesity with knee osteoarthritis) and additional outcome and comparator studies. Topline dates: TRIUMPH-4 2025-12-11, TRIUMPH-1 2026-05-21, TRIUMPH-2 and -3 2026-07-23, TRANSCEND-T2D-2 (vs semaglutide 2 mg) 2026-10-28. TRIUMPH-1 (NEJM) and TRIUMPH-2 (Lancet) were published on 2026-09-29. Lilly restated in September 2026 that it plans to submit to the FDA in Q1 2027. Patent filings are held by Eli Lilly.
What the data say
In the mid-stage weight-loss trial, people on the highest dose lost about 24% of their body weight in 48 weeks. They were still losing weight when the trial ended. A smaller liver study within that trial found that most people’s liver fat dropped to a normal level. In the late-stage (Phase 3) trials, Lilly reports these average weight losses at 80 weeks:
about 28% in people without diabetes
about 21% in people with type 2 diabetes
about 23% in people with heart disease
The first two of these trials were published in medical journals in September 2026. The published figures count everyone who started the trial, whether or not they stayed on the drug, so they are a little lower than the company’s figures, which count only people who stayed on it: about 25% in people without diabetes and about 19% in people with type 2 diabetes, at the top dose. The heart-disease and knee-arthritis results are still company reports. In a head-to-head trial reported in October 2026, people with type 2 diabetes lost about 21% on the top dose versus about 9% on Ozempic 2 mg (also a company report so far). The main side effects were an upset stomach while the dose was being raised, a faster heartbeat, odd skin feelings, and, in some people, low blood pressure.
Phase 2 (NCT04881760): 12 mg produced −24.2% body weight at 48 weeks vs −2.1% placebo; 100% of the 8 and 12 mg groups reached 5% or greater loss. The MASLD sub-study (n=98) reported relative liver-fat reductions of −81.4% (8 mg) and −82.4% (12 mg) at 24 weeks, with normal liver fat (under 5%) in 79% and 86%. Dose-dependent heart-rate increases peaked at 24 weeks and declined thereafter. Phase 3 toplines (company disclosures, efficacy estimand): TRIUMPH-1 −28.3% at 12 mg vs −2.2% placebo at 80 weeks, and −30.3% at 104 weeks in the BMI 35 or higher extension; TRIUMPH-2 −20.8% vs −4.0% with HbA1c down 1.5–1.6 points at 9–12 mg; TRIUMPH-3 −22.6% vs −3.2%; TRIUMPH-4 −28.7% at 68 weeks. TRIUMPH-1 (Jastreboff et al., NEJM, 2026-09-29) and TRIUMPH-2 (Bellido et al., Lancet, 2026-09-29) are now published; their treatment-regimen estimands at 12 mg are −25.0% vs −3.9% and −18.8% vs −5.1%, with TRIUMPH-2 reporting diarrhoea in 27–34%, nausea in 14–28%, hypotension in 1–6% and dysaesthesia in 4–7% of retatrutide groups. TRIUMPH-3, TRIUMPH-4 and the October 2026 TRANSCEND-T2D-2 head-to-head against semaglutide 2 mg (HbA1c −2.2 vs −1.8 points; weight −20.9% vs −9.4% at 12 mg) remain company disclosures.
Regulatory picture
Retatrutide is not approved anywhere. As of its July 2026 update, Lilly had not yet asked for approval. The FDA says retatrutide cannot legally be used by compounding pharmacies (places that mix their own versions of drugs). The FDA also says it is not part of any FDA-approved drug. The FDA has sent warning letters about retatrutide to online health companies, to ingredient sellers, and to sellers of products labelled “research use”. Products sold online as “retatrutide” are unapproved drugs. No one can be sure what is really in them.
Retatrutide is an investigational new drug under IND. It is not a component of any approved product and has no USP monograph. FDA’s guidance page on unapproved GLP-1 drugs states that retatrutide cannot be used in compounding under federal law, so neither the 503A nor the 503B pathway is available. FDA reports warning letters to telehealth companies for marketing retatrutide directly to consumers, to active pharmaceutical ingredient distributors for selling it to compounders, to outsourcing facilities for repackaging it, and to firms selling it labelled “for research purposes”. Lilly has said it plans a US marketing submission in the first quarter of 2027 based on the TRIUMPH program.
Dose
Doses reported in trials and studies
How dosing worked in the studies
In the trials, doses were given as a shot under the skin once a week. People were assigned by chance to retatrutide or a dummy treatment (placebo). TRIUMPH-1 and TRIUMPH-2 (80 weeks) and TRANSCEND-T2D-1 (40 weeks) tested 4, 9 or 12 mg in adults with obesity, overweight or type 2 diabetes. TRIUMPH-3 (80 weeks) and TRIUMPH-4 (68 weeks) tested 9 or 12 mg against placebo. The Phase 2 weight-loss study included 338 adults. It aimed for doses of 1, 4, 8 or 12 mg, or placebo, for 48 weeks. Some groups started at 2 or 4 mg and then went up. An early Phase 1b trial included 72 adults with type 2 diabetes. They got 0.5 to 12 mg, placebo, or the drug dulaglutide 1.5 mg for 12 weeks. The two highest-dose groups went up step by step.
Doses used in the studies are in the Scientific view.
Doses reported in studies, exactly as the cited trial reported them. They are not personal dosing instructions. Population, route and schedule matter more than the number.
Phase 2 obesity study: 338 adults with obesity or overweight plus comorbidity, no diabetes. Dose: 1, 4, 8 or 12 mg subcutaneous once weekly, with starting doses of 2 or 4 mg and escalation, 48 weeks. Result: −24.2% body weight at 12 mg vs −2.1% placebo at 48 weeks (Jastreboff et al., NEJM 2023)
Phase 2 type 2 diabetes study: 281 adults with type 2 diabetes. Dose: 0.5 to 12 mg subcutaneous once weekly vs placebo and dulaglutide 1.5 mg, 36 weeks. Result: HbA1c −2.02 points at 12 mg vs −0.01 placebo at 24 weeks; body weight −16.9% at 12 mg at 36 weeks (Rosenstock et al., Lancet 2023)
TRIUMPH-1: 2,339 adults with obesity, or overweight plus a weight-related condition, without diabetes; includes knee osteoarthritis and sleep apnoea sub-studies. Dose: 4, 9 or 12 mg subcutaneous once weekly vs placebo, 80 weeks; extension to 104 weeks in participants with BMI 35 or higher. Result: −17.6%, −23.7% and −25.0% body weight at 4, 9 and 12 mg vs −3.9% placebo at 80 weeks (treatment-regimen estimand; Jastreboff et al., NEJM, published online 2026-09-29). Lilly's May 2026 efficacy-estimand figures were −19.0%, −25.9% and −28.3% vs −2.2%. Knee-pain (WOMAC) and sleep-apnoea (AHI) sub-studies also improved vs placebo.
TRIUMPH-2: 1,152 adults with type 2 diabetes and obesity or overweight (BMI 27 or higher). Dose: 4, 9 or 12 mg subcutaneous once weekly vs placebo, 80 weeks. Result: −11.9%, −16.8% and −18.8% body weight at 4, 9 and 12 mg vs −5.1% placebo at 80 weeks, with improved glycaemic control (treatment-regimen estimand; Bellido et al., Lancet 2026;408:1455–1472, published online 2026-09-29). Lilly's July 2026 efficacy-estimand figures were −12.7%, −19.1% and −20.8% vs −4.0%, with HbA1c down 1.4–1.6 points vs 0.2. Discontinuation for adverse events or death 4%, 12% and 8% vs 5%.
TRIUMPH-3: 1,949 adults with BMI 35 or higher and established cardiovascular disease, with or without type 2 diabetes. Dose: 9 or 12 mg subcutaneous once weekly vs placebo, 80 weeks. Result: Company-reported July 2026: −21.6% and −22.6% body weight vs −3.2% placebo at 80 weeks (efficacy estimand). The primary endpoint was body weight; cardiovascular events were few (3-point MACE hazard ratio 1.12, 95% CI 0.64–1.96). Peer-reviewed publication pending.
TRIUMPH-4: 445 adults with obesity or overweight and knee osteoarthritis. Dose: 9 or 12 mg subcutaneous once weekly vs placebo, 68 weeks. Result: Company-reported December 2025: up to −28.7% body weight at 12 mg and WOMAC pain reduced by up to 4.5 points (75.8%) at 68 weeks. Peer-reviewed publication pending.
TRANSCEND-T2D-2: 1,298 adults with type 2 diabetes taking metformin. Dose: 9 or 12 mg subcutaneous once weekly vs semaglutide (Ozempic) 2 mg once weekly, open-label. Result: Company-reported October 2026: HbA1c −2.2 points at both doses vs −1.8 with semaglutide 2 mg; body weight −19.5% and −20.9% vs −9.4%; discontinuation for adverse events 4.8% and 7.9% vs 2.7%. Peer-reviewed publication pending.
2,339 adults with obesity, or overweight plus a weight-related condition, without diabetes; includes knee osteoarthritis and sleep apnoea sub-studies
4, 9 or 12 mg subcutaneous once weekly vs placebo, 80 weeks; extension to 104 weeks in participants with BMI 35 or higher
−17.6%, −23.7% and −25.0% body weight at 4, 9 and 12 mg vs −3.9% placebo at 80 weeks (treatment-regimen estimand; Jastreboff et al., NEJM, published online 2026-09-29). Lilly's May 2026 efficacy-estimand figures were −19.0%, −25.9% and −28.3% vs −2.2%. Knee-pain (WOMAC) and sleep-apnoea (AHI) sub-studies also improved vs placebo.
1,152 adults with type 2 diabetes and obesity or overweight (BMI 27 or higher)
4, 9 or 12 mg subcutaneous once weekly vs placebo, 80 weeks
−11.9%, −16.8% and −18.8% body weight at 4, 9 and 12 mg vs −5.1% placebo at 80 weeks, with improved glycaemic control (treatment-regimen estimand; Bellido et al., Lancet 2026;408:1455–1472, published online 2026-09-29). Lilly's July 2026 efficacy-estimand figures were −12.7%, −19.1% and −20.8% vs −4.0%, with HbA1c down 1.4–1.6 points vs 0.2. Discontinuation for adverse events or death 4%, 12% and 8% vs 5%.
1,949 adults with BMI 35 or higher and established cardiovascular disease, with or without type 2 diabetes
9 or 12 mg subcutaneous once weekly vs placebo, 80 weeks
Company-reported July 2026: −21.6% and −22.6% body weight vs −3.2% placebo at 80 weeks (efficacy estimand). The primary endpoint was body weight; cardiovascular events were few (3-point MACE hazard ratio 1.12, 95% CI 0.64–1.96). Peer-reviewed publication pending.
445 adults with obesity or overweight and knee osteoarthritis
9 or 12 mg subcutaneous once weekly vs placebo, 68 weeks
Company-reported December 2025: up to −28.7% body weight at 12 mg and WOMAC pain reduced by up to 4.5 points (75.8%) at 68 weeks. Peer-reviewed publication pending.
Active, not recruiting (topline reported October 2026)
1,298 adults with type 2 diabetes taking metformin
9 or 12 mg subcutaneous once weekly vs semaglutide (Ozempic) 2 mg once weekly, open-label
Company-reported October 2026: HbA1c −2.2 points at both doses vs −1.8 with semaglutide 2 mg; body weight −19.5% and −20.9% vs −9.4%; discontinuation for adverse events 4.8% and 7.9% vs 2.7%. Peer-reviewed publication pending.
Doses in other published studies
Published studies not listed in the trials table above: smaller or unregistered human studies first, then animal and cell studies. Doses are shown exactly as each study reported them. Animal studies report weight-based doses, absolute amounts or concentrations; none translates directly to people, and none is converted here.
Subjects
Design
Dose
Finding
Source
Humans: 4 healthy volunteers (2 male, 2 female; mean age 36.8 years) who obtained and self-administered retatrutide themselves; an aliquot of the material was checked in-house by high-resolution mass spectrometry and its identity confirmed
Unregistered elimination/detection study for anti-doping analysis (Brazil), plasma and urine sampling over 56 days, ethics-committee approved
2 mg subcutaneously on Day 1 and Day 7 (two doses total)
Retatrutide was detected in plasma of all four volunteers from 2 h after dosing and remained detectable in all four at the last sample, 56 days after the first dose, while neither intact drug nor metabolite signals were detected in urine at any time point.
0.5 mg, 1.5 mg, 3 mg, 3/6 mg or 3/6/9/12 mg subcutaneously once weekly for 12 weeks (top two cohorts reached their final dose by stepwise escalation within the trial)
Pharmacokinetics were dose-proportional with a half-life of about 6 days; at week 12 the three highest dose groups lowered placebo-adjusted HbA1c by 1.2-1.6 percentage points, placebo-adjusted body weight reduction appeared dose-dependent (up to 8.96 kg in the 3/6/9/12 mg group), and gastrointestinal events were the most frequent adverse events.
Humans: 537 adults with type 2 diabetes inadequately controlled by diet and exercise (HbA1c 7.0-9.5%, BMI 23 or higher) at 48 sites in the USA, Mexico and India
4 mg, 9 mg or 12 mg subcutaneously once weekly vs placebo, 40 weeks
By the treatment-regimen estimand, HbA1c changed by -1.69, -1.86 and -1.94 percentage points vs -0.81 with placebo and body weight by -11.5%, -13.9% and -15.3% vs -2.6% at week 40, with 2-5% discontinuing for adverse events on retatrutide vs 0% on placebo.
Mice: male C57BL/6JRj diet-induced obese MASH model (n = 8 per group); Hamsters: male golden Syrian hamsters on a free-choice high-fat/high-cholesterol diet with 10% fructose water
Preclinical vehicle-controlled efficacy study in two rodent models
15 nmol/kg subcutaneously every 3 days for 5 weeks (both species)
In mice body weight fell 31% vs vehicle with lower HOMA-IR and hepatic steatosis score, but the inflammation score was unchanged and the fibrosis score rose; in hamsters weight, HOMA-IR, plasma triglycerides and LDL-cholesterol fell and hepatic triglyceride content dropped 50%, without a reduction in liver histopathology score.
Mice: male MC4R knockout (genetic obesity) model, 35 weeks old
Unblinded, vehicle-controlled comparative study vs semaglutide and tirzepatide (0.05 mg/kg); the paper gives the semaglutide dose as 0.5 mg/kg in the methods and 0.1 mg/kg in the results
0.05 mg/kg subcutaneously once daily for 21 days
Retatrutide reduced body weight by 24.1 ± 5.8% (semaglutide 19.7%, tirzepatide 31.6%), and all three drugs significantly reduced both fat and lean mass.
Human tissue: isolated right atrial preparations from adults with severe coronary heart disease undergoing open-heart surgery
Ex vivo organ-bath contractility study
Cumulative concentrations from 10 nM up to 100 nM (highest tested), alone and with 1 µM cilostamide
Retatrutide increased atrial force of contraction in a concentration- and time-dependent manner, an effect reduced by GLP-1, GIP and glucagon receptor antagonists but not by propranolol.
Examples for the freeze-dried powder, as reported by protocol websites, not taken from studies. The water amount only sets the concentration (how much is in each mL); it does not change how much of the compound is in the vial. Each concentration assumes the vial really holds its labelled amount and the final liquid volume equals the water added.
Vial
Water added
Concentration
10 mg
2.0 mL
5 mg/mL
12 mg
1.2 mL
10 mg/mL
24 mg
2.4 mL
10 mg/mL
Clean the rubber tops of both vials with an alcohol swab.
Add the water slowly, letting it run down the inside wall of the vial rather than onto the powder.
Swirl or roll gently until the powder dissolves; protocol sites advise against shaking.
The liquid should be clear. If it is cloudy or has specks in it, do not use it. Clear liquid does not show that the product is pure, the right strength or sterile.
Write the date and the concentration on the vial, and keep it in the fridge (2–8 °C). No safe storage time after mixing has been established for these products.
Products sold as "research peptides" have not gone through FDA review for safety, effectiveness or quality. Bacteriostatic water does not sterilize a contaminated powder. It contains benzyl alcohol, and its label says it is not for use in newborns. To work out a volume from your own numbers, use the converter.
Doses described in clinical or compounding practice
From FDA labels and documents, other regulators, published reviews and professional references, as each source states them. Unless a source says otherwise, these describe practice or proposals, not results tested in trials. Reading doses safely: how concentration and syringe markings work.
This single-author case report from the Edinburgh Royal Infirmary describes a man in his mid-30s with type 1 diabetes. Two days before admission he gave himself a subcutaneous abdominal injection of an online-sourced product marketed as retatrutide and labelled "not for human or veterinary consumption", and he "reported intending to administer 0.5mg." The author notes that the product's composition, concentration and purity were unverified, so the adverse effects may have reflected inaccurate dosing, contaminants or a substituted compound. Because of that and a concurrent Shigella infection, causality cannot be established. (Branine N. Online-Sourced Retatrutide Complicating Impending Diabetic Ketoacidosis in a Patient With Type 1 Diabetes and Concurrent Shigella Gastroenteritis. Cureus 18(8):e115260, 2026, Peer-reviewed)
FDA's March 31, 2026 warning letter quotes the firm's "The Ultimate Mile High Compounds Peptide Cheat Sheet" for "GLP-3 RT (Retatrutide)": "Dosing: Start: 1mg - 2mg weekly. Titrate up to: 12mg weekly." The product labeling said "in vitro research and educational purposes only" and "not for human or veterinary consumption". FDA cited this seller material as evidence that the products were intended as drugs for human use and were unapproved new drugs. FDA does not endorse this regimen. (FDA warning letter to Mile High Compounds LLC (MARCS-CMS 721600), March 31, 2026, FDA document)
FDA's September 9, 2025 warning letter quotes the firm's website: "The standard, FDA-approved dosing schedule for Retatrutide is: Month 1: 0.25 mg per week…". FDA replied that "Compounded drug products are not FDA-approved" and that the claims were "false or misleading". It added that retatrutide "is not a component of an FDA-approved human drug", so no FDA-approved retatrutide dosing schedule exists. (FDA warning letter to GenLabMeds (MARCS-CMS 713650), September 9, 2025, FDA document)
Doses reported in online communities (untested)
Unverified, and not a recommendation. These are amounts people describe in online forums such as Reddit, collected so researchers can see how practice differs from the evidence. These forum accounts are not clinical evidence, even where they overlap studied doses. Products sold online as "research peptides" are not FDA approved, and their identity, purity and strength are not verified; they can be mislabeled, contaminated or wrongly dosed.
What people report
In the threads reviewed (r/Retatrutide and r/Peptides, May to September 2026), people described subcutaneous injection of retatrutide obtained outside trials, at weekly amounts from about 0.1 mg up to 10-12 mg; many described 1 to 6 mg per week, and a few described 15-28 mg, criticised by others. The main disagreement was whether poor responses came from fake or under-dosed product or from dosing errors. Reported side effects: gastrointestinal (nausea, vomiting, diarrhoea, constipation), fatigue, heart-rate rises, burning or painful skin sensitivity, poor sleep, and anhedonia or low mood.
How this compares with the studies
Published trials gave 0.5-12 mg subcutaneously once weekly using pharmaceutical-grade drug in monitored populations. Community amounts overlap that span and extend above it, using products of unverified identity and content, often alongside other compounds, so they cannot be compared with trial data for exposure, safety or efficacy. Threads referred to trial arms when debating a 2 mg starting amount; self-reports cannot show how often side effects occur or their cause.
Open questions a study would need to answer
What do the published Phase 3 papers report about how heart-rate changes and dysaesthesia vary with dose and over time?
What share of the weight lost in retatrutide trials was lean mass, and what did the Phase 2 body-composition substudy in type 2 diabetes report?
What have published analyses of products sold as retatrutide outside trials found about identity, purity and content?
2026-09-01 · FDA statement and warning letters: FDA's page on unapproved GLP-1 drugs (current as of this date) states that retatrutide cannot be used in compounding under federal law and is not a component of any FDA-approved drug. FDA has warned telehealth companies marketing retatrutide, API distributors selling it to compounders, outsourcing facilities repackaging it, and sellers of products labelled "for research purposes" or "not for human consumption". (source)
2026-08-24 · Warning letters (research-use sellers): A batch of FDA warning letters to online "research peptide" sellers (Peak Performance Peptides and others) named retatrutide among products FDA considers unapproved new drugs despite "research use only" labelling; an earlier letter to Gram Peptides (2026-03-31) made the same point. (source)
Side effects and warnings
Common side effects are nausea, vomiting, diarrhea and constipation. They were more common at higher doses and while the dose was being raised.
Heart rate went up. In Phase 2 this peaked around week 24 and then went down.
Some people had odd or painful skin feelings: 5.1–12.5% on retatrutide versus 0.9% on placebo in TRIUMPH-1 (company-reported), and 4–7% versus 1% in the published diabetes trial.
Low blood pressure symptoms were more common at higher doses: 1–6% versus under 1% on placebo in the published diabetes trial, and the published obesity trial also noted dose-dependent symptoms of low blood pressure.
Up to 11.3% of people at 12 mg stopped because of side effects, versus 4.9% on placebo in TRIUMPH-1. Up to 13.5% stopped in TRIUMPH-3 (company-reported).
Warnings for similar GLP-1 drugs are expected to apply too: inflamed pancreas, gallbladder problems, and a thyroid tumour warning. Long-term safety data are not published yet.
There is no approved label, so no official list of who should not use it exists. Trials left out people with a personal or family history of a thyroid cancer called medullary thyroid carcinoma, or MEN 2. No drug-interaction studies are published. It slows how fast the stomach empties, so it is expected to change how pills taken by mouth are absorbed.
Full lists are in the .
Reported side effects
Nausea, vomiting, diarrhea and constipation, dose-dependent and most frequent during escalation (Phase 2 and Phase 3)
Increased heart rate, peaking around week 24 and declining thereafter (Phase 2)
Dysaesthesia (altered or painful skin sensation) in 5.1–12.5% of retatrutide-treated participants vs 0.9% on placebo in TRIUMPH-1 (company-reported), and 4–7% vs 1% in TRIUMPH-2 (Lancet 2026)
Diarrhoea in 27–34% and nausea in 14–28% of retatrutide groups vs 13% and 8% on placebo in TRIUMPH-2 (Lancet 2026)
Hypotension in 1–6% vs under 1% on placebo in TRIUMPH-2 (Lancet 2026); dose-dependent symptoms of hypotension also reported in TRIUMPH-1 (NEJM 2026)
Permanent discontinuation for adverse events or death 4%, 12% and 8% at 4, 9 and 12 mg vs 5% on placebo in TRIUMPH-2 (Lancet 2026); seven deaths across the trial, none judged related to study drug by investigators
Discontinuation for adverse events up to 11.3% at 12 mg vs 4.9% placebo in TRIUMPH-1, and up to 13.5% in TRIUMPH-3 (company-reported)
Class effects seen with GLP-1 receptor agonists (pancreatitis, gallbladder disease, thyroid C-cell warning) apply by extension; long-term safety data are not yet published
Interactions
No formal drug-interaction studies are published. Delayed gastric emptying is expected to affect absorption of oral drugs, as with other GLP-1 receptor agonists.
Contraindications
None established; no approved label exists. Trials excluded people with a personal or family history of medullary thyroid carcinoma or MEN 2.
Storage
No approved product exists, so there is no label storage guidance. Research-grade lyophilized powder is typically shipped and stored frozen; supplier claims for reconstituted stability are not label data.
General storage guidance commonly given for freeze-dried research peptides and powders, not stability data for this substance. Storage conditions and usable life depend on the specific product and formulation; follow its documented instructions.
Condition
Temperature
Temporary (transportation), in powdered form
15 °C – 25 °C / 59 °F – 77 °F
Short term (1–3 years)
2 °C – 8 °C / 36 °F – 46 °F
After reconstitution (28 days)
2 °C – 8 °C / 36 °F – 46 °F
Long term (2–5 years)
−20 °C / −4 °F or below
Product characteristics
Form: Investigational solution for subcutaneous injection; research grade sold as lyophilized powder
Stability: Lipidated for albumin binding; half-life supports once-weekly dosing (about 6 days in Phase 1)
Compound information
Synthetic single-chain peptide engineered from a GIP-based scaffold with a C20 fatty diacid for albumin binding. PubChem lists the formula as C221H342N46O68 (CID 171390338).
Molecule, patents, enforcement history, full trial tables and compound details are in the .
Common questions
What is Retatrutide?
Retatrutide is an experimental drug from the company Lilly. It is a short chain of amino acids (a peptide). It copies three body hormones at once: GIP, GLP-1 and glucagon. The first two are the same targets as the drug tirzepatide. Adding glucagon is meant to help the body burn more energy. It is also meant to clear fat from the liver. Lilly ran a large late-stage (Phase 3) weight-loss trial, published in a medical journal in September 2026. People on the highest dose lost about 25% of their body weight over 80 weeks, on average, counting everyone who started whether or not they stayed on the drug (about 28% by the company's count, which includes only those who stayed on it).
Is Retatrutide FDA approved?
Still in clinical trials; not FDA approved.
What have studies found?
In the main 80-week trial, now published in a medical journal, adults with obesity lost about 25% of their body weight at the top dose versus about 4% on a dummy treatment (placebo). Lilly's own way of counting, which includes only people who stayed on the drug, put it at about 28% versus 2%.
In people with type 2 diabetes, it also lowered blood sugar (HbA1c) more than placebo. The most common side effects were stomach and gut problems.
How was it dosed in studies?
In the trials, doses were given as a shot under the skin once a week. People were assigned by chance to retatrutide or a dummy treatment (placebo). TRIUMPH-1 and TRIUMPH-2 (80 weeks) and TRANSCEND-T2D-1 (40 weeks) tested 4, 9 or 12 mg in adults with obesity, overweight or type 2 diabetes. TRIUMPH-3 (80 weeks) and TRIUMPH-4 (68 weeks) tested 9 or 12 mg against placebo. The Phase 2 weight-loss study included 338 adults. It aimed for doses of 1, 4, 8 or 12 mg, or placebo, for 48 weeks. Some groups started at 2 or 4 mg and then went up. An early Phase 1b trial included 72 adults with type 2 diabetes. They got 0.5 to 12 mg, placebo, or the drug dulaglutide 1.5 mg for 12 weeks. The two highest-dose groups went up step by step.
What are the side effects and warnings?
Common side effects are nausea, vomiting, diarrhea and constipation. They were more common at higher doses and while the dose was being raised.
Heart rate went up. In Phase 2 this peaked around week 24 and then went down.
Some people had odd or painful skin feelings: 5.1–12.5% on retatrutide versus 0.9% on placebo in TRIUMPH-1 (company-reported), and 4–7% versus 1% in the published diabetes trial.
Low blood pressure symptoms were more common at higher doses: 1–6% versus under 1% on placebo in the published diabetes trial, and the published obesity trial also noted dose-dependent symptoms of low blood pressure.
Up to 11.3% of people at 12 mg stopped because of side effects, versus 4.9% on placebo in TRIUMPH-1. Up to 13.5% stopped in TRIUMPH-3 (company-reported).
Warnings for similar GLP-1 drugs are expected to apply too: inflamed pancreas, gallbladder problems, and a thyroid tumour warning. Long-term safety data are not published yet.
There is no approved label, so no official list of who should not use it exists. Trials left out people with a personal or family history of a thyroid cancer called medullary thyroid carcinoma, or MEN 2. No drug-interaction studies are published. It slows how fast the stomach empties, so it is expected to change how pills taken by mouth are absorbed.
Is it legal to buy as a "research peptide"?
Products sold as "research use only" or "not for human consumption" are not approved for use in people. That label does not make them legal to sell for human use, and their contents are not checked by any regulator.
References
This page summarises the published sources below. PeptideBasics101 does no original research. Trial doses and results are reported as the cited study or label reported them. Sources can themselves be wrong or superseded; if you find a statement here that does not match its source, please tell us through our corrections process. Sources were last checked on 2026-11-01.
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