Follow-up in the adult obesity trial (Jastreboff et al., New England Journal of Medicine, 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., Nature Medicine, 2024).
Nature Medicine, 2024Receptors with activity reported in LY3437943 laboratory assays: GIP, GLP-1 and glucagon (Coskun et al., Cell Metabolism, 2022).
Triple agonistWhy it matters
Why is Retatrutide studied?
Coskun et al. (Cell Metabolism, 2022) reported Retatrutide activity at GIP, GLP-1 and glucagon receptors in laboratory assays. Subsequent trials measured body weight, HbA1c and liver fat in defined adult populations (Jastreboff et al., New England Journal of Medicine, 2023; Rosenstock et al., The Lancet, 2023; Sanyal et al., Nature Medicine, 2024). These records concern experimental findings rather than Form Labs material.
Three pathways, not one.
Coskun et al. (Cell Metabolism, 2022) reported receptor-assay findings for LY3437943 at GIP, GLP-1 and glucagon receptors, alongside rodent observations. These experimental settings are distinct from the later clinical trial populations.
Jastreboff et al. (New England Journal of Medicine, 2023), Rosenstock et al. (The Lancet, 2023) and Sanyal et al. (Nature Medicine, 2024) measured body weight, HbA1c and liver fat in separate adult study populations. The observations remain specific to those studies.
Study observations
What laboratory observations have Retatrutide studies reported?
Coskun et al. (Cell Metabolism, 2022) reported activity at GIP, GLP-1 and glucagon receptors in laboratory assays of LY3437943. The paper also included animal models. Receptor measurements describe the experimental molecule and model; they do not establish findings for a Form Labs vial or predict an individual clinical outcome.
Retatrutide receptor assays Findings stay tied to the cited study and its model.
Laboratory receptor assays
Coskun et al. (Cell Metabolism, 2022) reported LY3437943 activity at GIP, GLP-1 and glucagon receptors in laboratory assays.
Animal models
Coskun et al. (Cell Metabolism, 2022) reported body-weight and blood-sugar measurements in rodents; these are animal observations.
Liver measurements
Sanyal et al. (Nature Medicine, 2024) measured liver fat by MRI in adults with fatty-liver disease; the trial findings are specific to that population.
Pharmacology at a glance
- Research code
- LY3437943
- Class
- Triple agonist - one molecule designed to switch on three receptor systems at once: GIP, GLP-1, and glucagon.
- Molecule
- A long-acting lab-made peptide (a short amino-acid chain) built to stay active in the body for longer.
- Reported half-life
- About 6 days in the Phase 1 study - 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 in the published literature for body weight in adults with obesity, 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, with no results recorded in this guide. Each area is a trial topic, not a product claim.
Study areas from the published literature.
Body weight / obesity
Jastreboff et al. (New England Journal of Medicine, 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 against a placebo and an approved diabetes medicine.
Phase 2 trial - Lancet, 2023Liver fat (fatty-liver disease)
Sanyal et al. (Nature Medicine, 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 rather than lean tissue.
Lancet Diabetes & Endocrinology, 2025Heart & blood markers
Blood pressure and blood-fat readings, tracked as extra measurements across the Phase 2 trials.
Phase 2 trials - secondary measuresPhase 3 results (pending)
TRIUMPH and TRANSCEND are the large Phase 3 programmes asking the longer-term safety and outcome questions. Results aren't out yet.
TRIUMPH / TRANSCENDThe studies
What did the Retatrutide studies find?
The Retatrutide record includes laboratory and animal findings (Coskun et al., Cell Metabolism, 2022), an adult obesity trial (Jastreboff et al., New England Journal of Medicine, 2023), and a fatty-liver substudy (Sanyal et al., Nature Medicine, 2024). The obesity trial recorded nausea and other gastrointestinal events, mostly mild to moderate. Its short follow-up does not establish 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, and tracked body weight, blood sugar, and liver fat.
- Studied in
- Lab cell tests plus rodents (rats and mice).
- Design
- A proof-of-concept study - 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. (Cell Metabolism, 2022) reported LY3437943 activity at glucagon, GLP-1 and GIP receptors in laboratory assays, with the strongest activity at GIP. The associated body-weight, blood-sugar and liver-fat observations were in rodents rather than people.
DOI 10.1016/j.cmet.2022.07.013The first human study focused on safety and on how the body handled the molecule, with some early body-weight and blood-sugar readings along the way.
- Studied in
- Adults with type 2 diabetes.
- Design
- Randomised, double-blind, placebo-controlled - people were assigned by chance, neither side knew who got what, and one group got an inactive look-alike.
- Measured
- Safety, how the body absorbed and cleared the molecule, and early body-weight and blood-sugar readings.
Urva et al. (The Lancet, 2022) reported tolerability and pharmacokinetic observations in adults, including a blood half-life of about 6 days. These are early clinical measurements of the experimental molecule.
DOI 10.1016/S0140-6736(22)02033-5Jastreboff et al. (New England Journal of Medicine, 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. (New England Journal of Medicine, 2023) reported nausea and other gastrointestinal 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 against both a placebo and an approved diabetes medicine, tracking 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 (an approved medicine used as a benchmark).
- Measured
- HbA1c (a three-month blood-sugar marker) and body-weight change.
Rosenstock et al. (The Lancet, 2023) reported HbA1c and body-weight differences among study groups in adults with type 2 diabetes. These are group-level clinical observations.
DOI 10.1016/S0140-6736(23)01053-XSanyal et al. (Nature Medicine, 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. (Nature Medicine, 2024) reported liver-fat differences among groups in adults with metabolic dysfunction-associated steatotic liver disease. This was a smaller substudy with MRI measurements 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 rather than 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 came down more than with placebo or the approved comparison medicine, which helped show that most of the weight change was fat rather than lean tissue (Coskun T and colleagues - Lancet Diabetes & Endocrinology - 2025).
DOI 10.1016/S2213-8587(25)00092-0Compare
How does Retatrutide compare with similar compounds?
Retatrutide acts on three receptor systems, compared with two for tirzepatide and one for semaglutide. All three compounds act on GLP-1, tirzepatide and Retatrutide add GIP, and only Retatrutide adds glucagon. The table below also lists each compound's approval status, as recorded in this guide, and describes literature only, not product-use guidance.
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. (New England Journal of Medicine, 2023) reported nausea, vomiting, diarrhoea and constipation in the Retatrutide adult obesity trial. These events were mostly mild to moderate. Heart-rate increases peaked around the middle of follow-up in the same trial. These observations describe the clinical study population, and the short follow-up does not establish long-term safety.
Gastrointestinal events
Most commonJastreboff et al. (New England Journal of Medicine, 2023) reported nausea, vomiting, diarrhoea and constipation in adults with obesity; these events were mostly mild to moderate and were a reason for some participants to leave the trial.
Faster heart rate
Recorded during follow-upJastreboff et al. (New England Journal of Medicine, 2023) recorded heart-rate increases that peaked around week 24 and then declined in adults with obesity; the trial did not establish long-term cardiac outcomes.
Serious & unknown risks
Not establishedThe Phase 2 trials didn't 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 - these are the questions Phase 3 is built to answer.
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 cited in this guide do not establish long-term safety, heart and blood-vessel outcomes, or what happens after stopping. The trials cited in this guide did not study pregnancy and breastfeeding, enrolled adults only, and did not test type 1 diabetes. This guide's 2025 timeline entry lists the Phase 3 programmes TRIUMPH and TRANSCEND, which this guide names as the source of dedicated heart and blood-vessel data, with no results recorded here.
- Pregnancy & breastfeeding: not studied - these groups were left out of the trials.
- Children & under-18s: the trials enrolled adults only.
- Type 1 diabetes: not tested; the trials focused on obesity and type 2 diabetes.
- Long-term use: whether the changes last, and what safety looks like beyond the trial windows, is unknown.
- Heart & blood-vessel outcomes: dedicated data is still pending from the Phase 3 trials.
- After stopping: how much weight comes back after stopping isn't well described yet.
Development and status
Is Retatrutide approved, and where does the research stand?
Retatrutide is described in this guide as investigational, with the Phase 3 programmes TRIUMPH and TRANSCEND listed as underway in its 2025 timeline entry and no regulator decision recorded. The guide's timeline runs from the 2022 discovery and first human papers (Coskun et al., Cell Metabolism, 2022; Urva et al., The Lancet, 2022) through the 2023 Phase 2 trials (Jastreboff et al., New England Journal of Medicine, 2023; Rosenstock et al., The Lancet, 2023).
Discovery plus 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 cited in this guide are large and consistent across body weight, blood sugar and liver fat, but follow-up was short. The cited studies do not establish long-term safety or what happens after stopping, and every trial cited in this guide was funded by Eli Lilly, the maker. Independent Phase 3 confirmation matters. This guide is a summary of published research, not a product result or a promise.
The Phase 2 results are striking
The cited trials measured body weight, HbA1c and liver fat in different adult populations (Jastreboff et al., New England Journal of Medicine, 2023; Rosenstock et al., The Lancet, 2023; Sanyal et al., Nature Medicine, 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 aren't established. The Phase 3 trials, TRIUMPH and TRANSCEND, are underway and not yet published.
Safety observations
Jastreboff et al. (New England Journal of Medicine, 2023) reported gastrointestinal events and heart-rate increases in adults with obesity; the follow-up was short.
The maker ran the trials
Every trial here was funded by Eli Lilly, the company developing the drug. That's normal at this stage, but it's 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's 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 laboratory research. Matching current certification is unverified.
Lab handling
How is Retatrutide handled as reference material?
Retatrutide is laboratory reference material, 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. Historical sample reports do not verify current lot identity, purity or release status.
Research-use boundary
Retatrutide is supplied strictly for laboratory research. It is not for human consumption, veterinary, medical, or cosmetic use.
Storage
Supplied freeze-dried. Keep it at 2-8 C (fridge-cold) and out of light, following the vial label, any verified matching lab report for the batch, and 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. Matching current certification is unverified. For laboratory 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 handling 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, used to track diabetes.
- MASLD
- Metabolic dysfunction-associated steatotic liver disease - excess fat in the liver linked to metabolic health.
- MRI-PDFF
- An MRI measurement of how much of the liver is fat.
- Pharmacokinetics
- How the body absorbs, moves around, and clears a compound - including half-life.
- RCT
- Randomised controlled trial - people are assigned by chance and compared with another group, often a placebo.
- Adverse event
- Any unwanted medical event during a trial, whether or not it was caused by the compound.
- Investigational
- Still in research - not approved by regulators for use.
FAQ
What are the most common questions about Retatrutide?
The most common questions about Retatrutide concern 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. Retatrutide (research code LY3437943) is described in this guide as an investigational peptide from Eli Lilly and appears here only as a research subject in the published literature.
An investigational lab-made peptide (research code LY3437943) from Eli Lilly, now in Phase 3 trials. Published studies describe one molecule that acts on three receptor systems - GLP-1, GIP and glucagon - with body weight, blood sugar and liver fat tracked as trial results.
Coskun et al. (Cell Metabolism, 2022) reported LY3437943 activity at GIP, GLP-1 and glucagon receptors in laboratory assays. The term triple agonist describes that assay finding, separate from any clinical outcome.
Coskun et al. (Cell Metabolism, 2022) reported LY3437943 activity at GIP, GLP-1 and glucagon receptors in laboratory assays; the Tirzepatide discovery record reported GIP and GLP-1 activity (Coskun et al., Molecular Metabolism, 2018). The guide records semaglutide and tirzepatide as approved medicines and Retatrutide as investigational.
No. It's investigational and not approved by the TGA (Australia's medicines regulator), the US FDA, the European EMA, or any other regulator, for any use. It appears here only as a research subject in the published literature.
The cited Phase 2 trials followed defined adult populations for limited periods (Jastreboff et al., New England Journal of Medicine, 2023; Rosenstock et al., The Lancet, 2023). They do not establish long-term safety, cardiac outcomes or outcomes after stopping. Funding in the trials cited by this guide came from Eli Lilly.
Form Labs supplies peptides strictly as laboratory research materials. This guide is a plain-English summary of published research that Form Labs did not run - 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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