Follow-up in the adult obesity trial (Jastreboff et al., 2023).
Phase 2 trial - New England Journal of Medicine, 2023Plain-English research guideLY3437943
Retatrutide research guide
Everything worth knowing, without the jargon.
Retatrutide (research code LY3437943) is an investigational lab-made peptide - a short chain of amino acids - developed by Eli Lilly and now in Phase 3 human trials. It's studied for acting on three receptor systems at once.
Form Labs materials are research reference materials, not the approved medicines; no Form Labs product is approved for human or veterinary use.
REV 2026-10 · 1 Oct 20266 peer-reviewed studiesResearch-use-only context
What the papers reportThird-party literature - not product claims
MRI follow-up in the smaller fatty-liver substudy (Sanyal et al., 2024).
Nature Medicine, 2024Receptors with activity reported in LY3437943 lab assays: GIP, GLP-1 and glucagon (Coskun et al., 2022).
Triple agonistWhy it matters
Why is Retatrutide studied?
Coskun et al. (2022) reported that Retatrutide acts at the GIP, GLP-1 and glucagon receptors in lab assays. Later trials measured body weight, HbA1c (a three-month blood sugar marker) and liver fat in set groups of adults (Jastreboff et al., 2023; Rosenstock et al., 2023; Sanyal et al., 2024). These are research findings, not results for Form Labs material.
Three pathways, not one.
Coskun et al. (2022) reported receptor-assay findings for LY3437943 at the GIP, GLP-1 and glucagon receptors, plus rodent observations. These lab settings differ from the later clinical trial groups.
Three papers measured body weight, HbA1c and liver fat in separate groups of adults: Jastreboff et al. (2023), Rosenstock et al. (2023) and Sanyal et al. (2024). The results apply only to those studies.
Study observations
What laboratory observations have Retatrutide studies reported?
Coskun et al. (2022) reported activity at the GIP, GLP-1 and glucagon receptors in lab assays of LY3437943. The paper also used animal models. Receptor tests describe the test molecule and the test model. They do not give findings for a Form Labs vial. They do not predict what any one person would see.
Retatrutide receptor assays Findings stay tied to the cited study and its model.
Laboratory receptor assays
Coskun et al. (2022) reported LY3437943 activity at the GIP, GLP-1 and glucagon receptors in lab assays.
Animal models
Coskun et al. (2022) reported body weight and blood sugar measurements in rodents. These are animal observations.
Liver measurements
Sanyal et al. (2024) measured liver fat by MRI in adults with fatty-liver disease. The findings apply only to that group.
Pharmacology at a glance
- Research code
- LY3437943
- Class
- Triple agonist: one molecule designed to switch on three receptor systems at once. They are GIP, GLP-1 and glucagon.
- Molecule
- A long-acting lab-made peptide (a short chain of amino acids) built to stay active in the body for longer.
- Reported half-life
- About 6 days in the Phase 1 study. It is the time for the amount in the blood to fall by half.
- Originator
- Developed by Eli Lilly
- Approval status
- Still investigational. Phase 3 trials are underway before any regulator decides on approval.
What it has been studied for
What has Retatrutide been studied for?
Retatrutide has been studied for body weight in adults with obesity. It has also been studied for blood sugar control in type 2 diabetes, liver fat in fatty-liver disease, fat versus lean mass, and heart and blood markers. This guide's 2025 timeline entry also lists the Phase 3 programmes TRIUMPH and TRANSCEND. This guide records no results for them. Each area is a trial topic, not a product claim.
Study areas from the published literature.
Body weight / obesity
Jastreboff et al. (2023) measured body weight change in adults with obesity and no diabetes.
Phase 2 trial - New England Journal of Medicine, 2023Type 2 diabetes
Blood-sugar control (HbA1c) and body weight, compared with a placebo and an approved diabetes medicine.
Phase 2 trial - Lancet, 2023Liver fat (fatty-liver disease)
Sanyal et al. (2024) measured liver fat by MRI in adults with fatty-liver disease.
Nature Medicine, 2024Fat vs lean mass
Imaging over 36 weeks to work out how much of the weight change was fat and how much was lean tissue.
Lancet Diabetes & Endocrinology, 2025Heart & blood markers
Blood pressure and blood-fat readings, tracked as extra measures across the Phase 2 trials.
Phase 2 trials - secondary measuresPhase 3 results (pending)
TRIUMPH and TRANSCEND are the large Phase 3 programmes. They ask the longer-term safety and outcome questions. Results are not out yet.
TRIUMPH / TRANSCENDThe studies
What did the Retatrutide studies find?
The Retatrutide record includes lab and animal findings (Coskun et al., 2022). It includes an adult obesity trial (Jastreboff et al., 2023) and a fatty-liver substudy (Sanyal et al., 2024). The obesity trial recorded nausea and other gut events, mostly mild to moderate. The follow-up was short, so it does not show long-term safety.
Open any study for a plain summary, what it measured, the finding, and a link to the paper.
This was the first proof that one peptide could switch on all three receptor systems. The team tested it in lab cells and in rodents. They tracked body weight, blood sugar and liver fat.
- Studied in
- Lab cell tests plus rodents (rats and mice).
- Design
- A proof-of-concept study, which is an early check that the idea works at all.
- Measured
- How strongly the molecule bound each receptor, plus body weight and blood sugar in the animals.
Coskun et al. (2022) reported LY3437943 activity at the glucagon, GLP-1 and GIP receptors in lab assays. The activity was strongest at GIP. The body weight, blood sugar and liver-fat observations were in rodents, not people.
DOI 10.1016/j.cmet.2022.07.013The first human study. It looked at safety and at how the body handled the molecule. It also took some early body weight and blood sugar readings.
- Studied in
- Adults with type 2 diabetes.
- Design
- Randomised, double-blind and placebo-controlled. Chance decided who got what. Neither side knew who got which. One group got an inactive look-alike.
- Measured
- Safety, how the body took in and cleared the molecule, and early body weight and blood sugar readings.
Urva et al. (2022) reported tolerability and pharmacokinetic notes in adults, including a blood half-life of about 6 days. These are early clinical measures of the test molecule.
DOI 10.1016/S0140-6736(22)02033-5Jastreboff et al. (2023) measured body weight change against placebo over 48 weeks in adults with obesity.
- Studied in
- 338 adults with obesity and no diabetes.
- Design
- A 48-week randomised, double-blind, placebo-controlled trial.
- Measured
- Percent body weight change at 24 and 48 weeks.
Jastreboff et al. (2023) reported nausea and other gut events, mostly mild to moderate, in adults with obesity. The same trial recorded heart-rate increases during follow-up.
DOI 10.1056/NEJMoa2301972This trial compared Retatrutide with both a placebo and an approved diabetes medicine. It tracked blood sugar (HbA1c) and body weight.
- Studied in
- 281 adults with type 2 diabetes.
- Design
- A 36-week trial with a placebo group and an active comparator. This is an approved medicine used as a benchmark.
- Measured
- HbA1c (a three-month blood sugar marker) and body weight change.
Rosenstock et al. (2023) reported HbA1c and body weight differences between study groups in adults with type 2 diabetes. These are group-level clinical observations.
DOI 10.1016/S0140-6736(23)01053-XSanyal et al. (2024) measured liver fat by MRI at 24 weeks in a smaller group of adults with fatty-liver disease.
- Studied in
- 98 adults whose liver fat was at least 10% at the start.
- Design
- An imaging sub-study using MRI scans at 24 weeks.
- Measured
- Liver-fat change, as a percentage of each person's starting level.
Sanyal et al. (2024) reported liver-fat differences between groups of adults with metabolic dysfunction-associated steatotic liver disease. This was a smaller substudy with MRI measures at 24 weeks.
DOI 10.1038/s41591-024-03018-2This sub-study used body-composition imaging to work out how much of the weight change was fat and how much was lean tissue.
- Studied in
- Adults with type 2 diabetes.
- Design
- An imaging sub-study using body-composition scans up to week 36.
- Measured
- Total fat mass, compared with placebo and an approved medicine.
Total body-fat mass fell more than with placebo or the approved comparison medicine. This helped show that most of the weight change was fat, not lean tissue (Coskun T and colleagues, 2025).
DOI 10.1016/S2213-8587(25)00092-0Compare
How does Retatrutide compare with similar compounds?
Retatrutide acts on three receptor systems. Tirzepatide acts on two and semaglutide on one. All three compounds act on GLP-1. Tirzepatide and Retatrutide add GIP. Only Retatrutide adds glucagon. The table below also lists each compound's approval status, as recorded in this guide. It describes the literature only. It is not guidance on use.
This table describes literature and approval status only.
| Semaglutide (Ozempic / Wegovy) | Tirzepatide (Mounjaro / Zepbound) | Retatrutide (LY3437943) | |
|---|---|---|---|
| GLP-1 receptor | Yes | Yes | Yes |
| GIP (meal & insulin-response pathway) | - | Yes | Yes |
| Glucagon (energy & liver pathway) | - | - | Yes |
| Receptor systems acted on | 1 | 2 | 3 |
| Approval status | Approved medicine | Approved medicine | Investigational - in Phase 3 trials |
Comparison is for context from published records. It is not product-use guidance.
Risks recorded in studies
What risks have Retatrutide studies recorded?
Jastreboff et al. (2023) reported nausea, vomiting, diarrhoea and constipation in the Retatrutide adult obesity trial. These events were mostly mild to moderate. Heart rate went up, with a peak around the middle of follow-up. These notes describe the people in the trial. The follow-up was short, so it does not show long-term safety.
Gastrointestinal events
Most commonJastreboff et al. (2023) reported nausea, vomiting, diarrhoea and constipation in adults with obesity. These events were mostly mild to moderate. They were a reason for some people to leave the trial.
Faster heart rate
Recorded during follow-upJastreboff et al. (2023) recorded heart-rate increases in adults with obesity. The rise peaked around week 24 and then fell. The trial did not show long-term heart outcomes.
Serious & unknown risks
Not establishedThe Phase 2 trials did not turn up an unexpected serious safety signal. But they were short. Long-term safety, heart and blood-vessel outcomes, rare events and what happens after stopping are still unknown. Phase 3 is built to answer these questions.
This section summarizes third-party trial records. It is not a complete safety profile or advice.
Where evidence stops
What has Retatrutide research not established?
The Retatrutide studies in this guide do not show long-term safety. They do not show heart and blood-vessel outcomes or what happens after stopping. They did not study pregnancy or breastfeeding. They enrolled adults only and did not test type 1 diabetes. This guide's 2025 timeline entry lists the Phase 3 programmes TRIUMPH and TRANSCEND. The guide names them as the source of dedicated heart and blood-vessel data. It records no results yet.
- Pregnancy and breastfeeding: not studied. These groups were left out of the trials.
- Children and under-18s: the trials enrolled adults only.
- Type 1 diabetes: not tested. The trials focused on obesity and type 2 diabetes.
- Long-term use: it is unknown whether the changes last. It is also unknown what safety looks like beyond the trial windows.
- Heart and blood-vessel outcomes: dedicated data is still pending from the Phase 3 trials.
- After stopping: it is not yet well described how much weight comes back after stopping.
Development and status
Is Retatrutide approved, and where does the research stand?
This guide describes Retatrutide as investigational. Its 2025 timeline entry lists the Phase 3 programmes TRIUMPH and TRANSCEND as underway. No regulator decision is recorded. The timeline starts with the 2022 discovery and first human papers (Coskun et al., 2022; Urva et al., 2022). It continues with the 2023 Phase 2 trials (Jastreboff et al., 2023; Rosenstock et al., 2023).
Discovery and the first-in-human study: early lab and animal work, then the Phase 1 safety study.
Phase 2 trials in obesity and type 2 diabetes reported the body weight and blood sugar results.
The liver-fat sub-study published its MRI imaging data in fatty-liver disease.
The body-composition sub-study used imaging to separate fat from lean tissue in the weight change.
The Phase 3 programmes, TRIUMPH and TRANSCEND, are underway. Results are still pending.
Approval status: Still investigational. Phase 3 trials are underway before any regulator decides on approval.Whatever the molecule’s status elsewhere, what Form Labs supplies is research-use-only reference material - for laboratory work, not for people or animals.
Evidence and limitations
What does the Retatrutide research mean, and what does it not?
The Retatrutide Phase 2 results in this guide are large and fairly consistent across body weight, blood sugar and liver fat. But follow-up was short. The studies do not show long-term safety or what happens after stopping. Eli Lilly, the maker, paid for every trial cited here. Independent Phase 3 confirmation matters. This guide sums up published research. It is not a product result or a promise.
The Phase 2 results are striking
The trials in this guide measured body weight, HbA1c and liver fat in different groups of adults (Jastreboff et al., 2023; Rosenstock et al., 2023; Sanyal et al., 2024). Their findings do not describe Form Labs material.
Follow-up is still short
Long-term safety, heart and blood-vessel outcomes, and what happens after stopping are not shown. The Phase 3 trials, TRIUMPH and TRANSCEND, are underway and not yet published.
Safety observations
Jastreboff et al. (2023) reported gut events and heart-rate increases in adults with obesity. The follow-up was short.
The maker ran the trials
Eli Lilly, the company developing the drug, paid for every trial here. That is normal at this stage. It is exactly why independent Phase 3 confirmation matters.
Where Form Labs fits
This guide is a plain-English summary of published research that Form Labs did not run. It is not medical advice, not a product claim and not use guidance. Form Labs supplies Retatrutide strictly as reference material, with a catalog lot record, for lab research.
Lab handling
How is Retatrutide handled as reference material?
Retatrutide is lab reference material. It is not for human consumption or veterinary use. Storage and lot checks follow the product label and any verified matching certificate of analysis (COA). This guide's catalogue record notes storage at 2-8 C and protection from light.
Research-use boundary
Retatrutide is supplied strictly for lab research. It is not for human consumption, or for veterinary, medical or cosmetic use.
Storage
Supplied freeze-dried. Keep it at 2-8 C (fridge-cold) and out of light. Follow the vial label, any verified matching lab report for the batch. The receiving lab's own written procedures.
Perth dispatch
Available to Perth researchers as RUO reference material, dispatched from Perth via Australia Post or CouriersPlease. For lab research use only.
Glossary
Plain-English definitions.
- Agonist
- A molecule that switches a receptor on.
- Triple agonist
- One molecule that switches on three different receptor systems at once.
- GLP-1
- A gut-hormone pathway tied to feeling full and to the stomach emptying more slowly.
- GIP
- A pathway involved in the insulin response and in how the body handles nutrients after a meal.
- Glucagon receptor
- A pathway linked to how the body uses energy and to liver fat.
- Incretin
- The gut-hormone family (including GLP-1 and GIP) studied for insulin and appetite signals.
- HbA1c
- A blood marker of average blood sugar over about three months. It is used to track diabetes.
- MASLD
- Metabolic dysfunction-associated steatotic liver disease. It means extra fat in the liver, linked to metabolic health.
- MRI-PDFF
- An MRI measure of how much of the liver is fat.
- Pharmacokinetics
- How the body takes in, moves around and clears a compound. Half-life is part of it.
- RCT
- Randomised controlled trial. Chance decides who goes in each group. One group is compared with another, often a placebo.
- Adverse event
- Any unwanted medical event during a trial, whether or not the compound caused it.
- Investigational
- Still in research. Regulators have not approved it for use.
FAQ
What are the most common questions about Retatrutide?
The common questions cover what Retatrutide is, what triple agonist means, how it differs from Ozempic and Mounjaro, how solid the evidence is, and what research use only means. This guide describes Retatrutide (research code LY3437943) as an investigational peptide from Eli Lilly. It appears here only as a research subject in the published literature.
Retatrutide (research code LY3437943) is an investigational lab-made peptide from Eli Lilly, now in Phase 3 trials. Published studies describe one molecule that acts on three receptor systems: GLP-1, GIP and glucagon. Trials tracked body weight, blood sugar and liver fat.
Coskun et al. (2022) reported LY3437943 activity at the GIP, GLP-1 and glucagon receptors in lab assays. The term triple agonist describes that lab finding. It is separate from any clinical result.
Coskun et al. (2022) reported LY3437943 activity at the GIP, GLP-1 and glucagon receptors in lab assays. The Tirzepatide discovery record reported GIP and GLP-1 activity (Coskun et al., 2018). This guide records semaglutide and tirzepatide as approved medicines and Retatrutide as investigational.
No. It is investigational. The TGA (Australia's medicines regulator), the US FDA, the European EMA and other regulators have not approved it for any use. It appears here only as a research subject in the published literature.
The Phase 2 trials in this guide followed set groups of adults for limited periods (Jastreboff et al., 2023; Rosenstock et al., 2023). They do not show long-term safety, heart outcomes or outcomes after stopping. Eli Lilly paid for the trials cited in this guide.
Form Labs supplies peptides strictly as lab research materials. This guide is a plain-English summary of published research that Form Labs did not run. It is not medical advice, not a product claim, and not guidance for any human or veterinary use.
References
Every figure, sourced.
Educational references to third-party literature. Form Labs is unaffiliated with the study authors.
Early lab and animal study of LY3437943 acting on the GIP, GLP-1 and glucagon receptors. Coskun T, Urva S, Roell WC, et al. Cell Metabolism, 2022; 34(9): 1234-1247.
DOIFirst-in-human safety study of LY3437943, including how the body absorbs and clears it. Urva S, Coskun T, Loh MT, et al. The Lancet, 2022; 400: 1869-1881.
DOIPhase 2 trial reporting body-weight results in adults with obesity and no diabetes. Jastreboff AM, Kaplan LM, Frias JP, et al. New England Journal of Medicine, 2023; 389(6): 514-526.
DOIPhase 2 trial reporting blood-sugar and body-weight results in adults with type 2 diabetes. Rosenstock J, Frias J, Jastreboff AM, et al. The Lancet, 2023; 402: 529-544.
DOISub-study reporting liver-fat results in fatty-liver disease (MASLD). Sanyal AJ, Kaplan LM, Frias JP, et al. Nature Medicine, 2024; 30: 2037-2048.
DOIImaging sub-study describing fat mass versus lean mass within the weight change. Coskun T, Wu Q, Schloot NC, et al. Lancet Diabetes & Endocrinology, 2025.
DOICitations are provided for education only. No therapeutic, weight-loss, or efficacy claims are made.
How we produce these guides
These guides are written and maintained in-house by the Form Laboratories research team. They summarise published literature and link to the cited papers. Form Laboratories did not run those studies. They are not authored by a named clinician and are not medical advice.
Findings remain tied to the study population, model and limits. Cell and animal observations remain separate from clinical results. Everything we supply is research-use-only reference material, not for people or animals.
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