Retatrutide: the basics
What is it?
A lab-made peptide medicine being tested by Eli Lilly. It switches on three hormone signals (GIP, GLP-1 and glucagon) that affect appetite, blood sugar and energy use.
Research paper 1 ↗Research paper 2 ↗Research paper 3 ↗What do people claim it helps with?
Large weight loss, better blood-sugar control in type 2 diabetes, and help with weight-related problems such as knee pain and sleep apnea.
What has research actually shown?
Large controlled trials in adults found much more average weight loss than placebo, and better blood sugar in people with type 2 diabetes. Average results do not predict what happens to one person.
Research paper 1 ↗Research paper 2 ↗Research paper 3 ↗Has this been demonstrated in people?
Phase 2 and phase 3 randomized trials in adults, run and paid for by the manufacturer. Long-term studies of heart and kidney outcomes are still running.
Research paper 1 ↗Research paper 2 ↗Research paper 3 ↗What side effects, risks and unknowns should I understand?
Nausea, diarrhoea and vomiting were common in trials. Some people had low blood pressure, a faster heart rate or unusual skin sensations. Long-term safety is not yet known.
FDA safety information 1 ↗Research paper 2 ↗Is it an approved medicine?
No FDA-approved medicine contains retatrutide. FDA says it has not been found safe and effective for any condition and has warned sellers of "research" versions.
FDA safety information ↗Approval here means U.S. FDA approval and applies to a particular product, formulation and use. This is a starting overview, not a complete side-effect list. Sources checked 10 October 2026; independent scientific review pending.
How is it used or studied?
Tested in trials as a once-weekly injection given under supervision. There is no approved product; online vials are not the trial medicine.
Different routes and formulations can have different effects. A study of one product does not validate every product with the same peptide name.
A common misunderstanding
Retatrutide is not tirzepatide or semaglutide. Strong trial results do not mean a product sold online is safe or genuine.
What should I ask a clinician?
- What diagnosis or goal are we trying to address, and what established options are available?
- Was the expected benefit shown in people like me, using this exact product?
- How could my medicines, health conditions or pregnancy plans affect the risks?
- What monitoring is needed, and what would tell us the treatment is helping or should be stopped?
What do the research words mean?
- Peptide
- A short chain of amino acids, the building blocks of proteins.
- Preclinical
- Research in cells, tissues or animals before dependable treatment evidence in people.
- Controlled trial
- A study comparing a treatment with another treatment or a placebo to help separate its effects from other explanations.
- Biomarker
- A measurement, such as a hormone level. A change does not necessarily mean someone feels better or lives longer.
Retatrutide Evidence & Clinical Profile
Human Study Limits
Retatrutide has been investigated in clinical contexts. Patient outcomes must be evaluated against study size, design, and control cohorts.
Laboratory & In Vivo Assays
Cellular and animal disease models examine receptor binding affinities and signaling cascades, which require human confirmation.
What is Retatrutide?
Retatrutide (LY3437943) is Retatrutide is an investigational once-weekly injectable peptide from Eli Lilly that activates three hormone receptors: GIP, GLP-1 and glucagon. Phase 3 trials published in 2026 reported large average weight loss, but it is not FDA-approved and long-term outcome trials are still running. Aliases include: LY3437943, GIP/GLP-1/glucagon triple agonist.
- Sequence (one-letter)
- N/A
- Molecular formula
- N/A
- Molecular weight
- N/A
- CAS Number
- 2381089-83-2
- UNII Code
- NOP2Y096GV
- PubChem CID
- N/A
Identifiers are for the free base; retatrutide sodium carries UNII LQ42M82ZU6. PubChem has no compound record yet.
Identifiers checked against PubChem and FDA's Global Substance Registration System on 13 October 2026. FDA substance record ↗ See all names and codes in the peptide name index.
Clinical Trials & Human Cohorts
Human research can examine tolerability, symptoms or patient outcomes. The design and comparator determine what each result can establish.
Retatrutide, a Triple Hormone Receptor Agonist, for Treatment of Obesity [1]
What was reported
Mean body-weight change ranged from −17.6% to −25.0% across the three retatrutide dose groups versus −3.9% with placebo. Knee-pain scores and sleep-apnea events per hour fell more than with placebo in the relevant subgroups.
What limits the conclusion
Funded by Eli Lilly. Gastrointestinal adverse events were the most common. Effects on heart attacks, strokes and deaths have not been shown; a separate outcomes trial is ongoing.
Retatrutide in adults with obesity and type 2 diabetes (TRIUMPH-2) [2]
What was reported
Mean body-weight change was −11.9% to −18.8% across retatrutide groups versus −5.1% with placebo; glucose control also improved.
What limits the conclusion
Diarrhoea, nausea, low blood pressure and dysesthesia (abnormal skin sensations) were more common than with placebo. Discontinuation because of adverse events or death reached 12% in one retatrutide group versus 5% with placebo.
Retatrutide in type 2 diabetes inadequately controlled with diet and exercise (TRANSCEND-T2D-1) [3]
What was reported
HbA1c fell by 1.69 to 1.94 percentage points with retatrutide versus 0.81 with placebo; body weight changed −11.5% to −15.3% versus −2.6%.
What limits the conclusion
Short 40-week trial in people with recently diagnosed diabetes (mean 2.5 years). No severe hypoglycaemia was reported, but longer and broader studies are needed.
Triple-Hormone-Receptor Agonist Retatrutide for Obesity - A Phase 2 Trial [4]
What was reported
At 48 weeks mean weight change ranged from −8.7% to −24.2% across dose groups versus −2.1% with placebo.
What limits the conclusion
Small groups and dose-finding design. Gastrointestinal effects were dose-related, and heart rate rose in a dose-dependent way, peaking at 24 weeks.
How the compound may work
Mechanisms describe how Retatrutide may affect biological processes. Laboratory findings and patient outcomes answer different questions.
Three receptors, one molecule
Laboratory assays showed retatrutide activates glucagon and GLP-1 receptors in a balanced way, with stronger GIP-receptor activity. In obese mice, the glucagon-receptor component added higher energy expenditure to the reduced food intake driven by GIP and GLP-1 signalling. Mouse findings do not prove the same balance in people. [5]
Liver fat reduction
In participants with fatty liver disease from the phase 2 obesity trial, liver fat fell sharply versus placebo, and the reductions tracked weight loss and markers of improved insulin sensitivity. [6]
Areas Being Studied
These research topics reflect active areas of scientific exploration, distinct from unverified commercial marketing claims.
Obesity and weight-related conditions
Weight loss, knee-osteoarthritis pain and obstructive sleep apnea in adults with obesity. [1]
Type 2 diabetes
Glucose control and body weight in adults with type 2 diabetes, with and without obesity. [3]
Fatty liver disease (MASLD)
Liver-fat reduction measured by imaging; biopsy-based outcome trials are a separate question. [6]
Cardiovascular and kidney outcomes
TRIUMPH-Outcomes is testing whether retatrutide changes cardiovascular and kidney events; results are not yet available. [9]
Compare the study designs.
| Study | Design / sample | Outcome type | Key limitation |
|---|---|---|---|
| TRIUMPH-1: obesity without diabetes · 2026 [1] | Phase 3 double-blind, placebo-controlled randomized trial; 80 weeks n = 2339 |
Clinical endpoint evaluation | Funded by Eli Lilly. Gastrointestinal adverse events were the most common. Effects on heart attacks, strokes and deaths have not been shown; a separate outcomes trial is ongoing. |
| TRIUMPH-2: obesity with type 2 diabetes · 2026 [2] | Phase 3 double-blind, placebo-controlled randomized trial; 80 weeks n = 1152 |
Clinical endpoint evaluation | Diarrhoea, nausea, low blood pressure and dysesthesia (abnormal skin sensations) were more common than with placebo. Discontinuation because of adverse events or death reached 12% in one retatrutide group versus 5% with placebo. |
| TRANSCEND-T2D-1: diabetes monotherapy · 2026 [3] | Phase 3 double-blind, placebo-controlled randomized trial; 40 weeks n = 537 |
Clinical endpoint evaluation | Short 40-week trial in people with recently diagnosed diabetes (mean 2.5 years). No severe hypoglycaemia was reported, but longer and broader studies are needed. |
| Phase 2 obesity trial · 2023 [4] | Phase 2 double-blind, placebo-controlled dose-finding randomized trial; 48 weeks n = 338 |
Clinical endpoint evaluation | Small groups and dose-finding design. Gastrointestinal effects were dose-related, and heart rate rose in a dose-dependent way, peaking at 24 weeks. |
Regulatory Status & Clinical Safety
Regulatory Classification
United States, checked 11 October 2026: not FDA-approved. No retatrutide product appears in Drugs@FDA. FDA states that retatrutide is not a component of any FDA-approved drug, has not been found safe and effective for any condition, and cannot be used in compounding; the agency has warned companies selling it as a "research" product. Products sold online are not the material tested in Lilly's trials.
Safety Realities & Impurities
Safety depends on the molecule, formulation, route and evidence. A laboratory purity measurement alone cannot establish safety for human use.
Clinical Trials Registry Records
Official registry records from ClinicalTrials.gov. Study registration does not imply government endorsement or guaranteed efficacy.
A Study of Retatrutide (LY3437943) in Participants Who Have Obesity or Overweight (TRIUMPH-1) [7]
- Planned enrollment
- 2335 (actual enrollment)
- Posted results
- Pending in registry
- Sponsor
- Eli Lilly and Company
- Last updated
- 2026-08-21
A Study of Retatrutide (LY3437943) in Participants With Type 2 Diabetes Mellitus Who Have Obesity or Overweight (TRIUMPH-2) [8]
- Planned enrollment
- 1152 (actual enrollment)
- Posted results
- Pending in registry
- Sponsor
- Eli Lilly and Company
- Last updated
- 2026-07-30
The Effect of Retatrutide Once Weekly on Cardiovascular Outcomes and Kidney Outcomes in Adults Living With Obesity (TRIUMPH-Outcomes) [9]
- Planned enrollment
- 10000 (estimated enrollment)
- Posted results
- Pending in registry
- Sponsor
- Eli Lilly and Company
- Last updated
- 2026-10-08
A Study of Retatrutide (LY3437943) Compared to Tirzepatide (LY3298176) in Adults Who Have Obesity (TRIUMPH-5) [10]
- Planned enrollment
- 800 (estimated enrollment)
- Posted results
- Pending in registry
- Sponsor
- Eli Lilly and Company
- Last updated
- 2026-07-20
WADA & Anti-Doping Regulations
WADA Anti-Doping Status
Retatrutide is not prohibited under current World Anti-Doping Agency (WADA) regulations. However, athletes must ensure unregulated preparations or unverified vendor products do not violate Section S0 (Non-approved substances). Last verified: October 2026.
Research Timeline
-
2022
Discovery and first-in-human data
Lilly describes LY3437943 and reports a phase 1 single-dose study. [5]
-
2023
Phase 2 obesity trial published
A 48-week dose-finding trial reports dose-related weight loss. [4]
-
2026
First phase 3 results
TRANSCEND-T2D-1 reports glucose and weight results in type 2 diabetes. [3]
-
2026
TRIUMPH-1 and TRIUMPH-2 published
Phase 3 obesity trials report 80-week weight results with and without diabetes. [1]
-
2026
Current status
Not FDA-approved. FDA warns that retatrutide sold as a "research" product is an illegal unapproved drug. [11]
What Researchers Still Don't Know
Long-term safety profiles
Multi-year observational data in broader heterogeneous cohorts remains uncharacterized.
Optimal dose-response thresholds
Comparative trials optimizing minimal effective exposure versus adverse event rates.
Formulation bioavailability
Differences between oral, subcutaneous, and modified peptide delivery vehicles.
References
Primary sources verified against PubMed / NLM and regulatory databases.
-
Phase 3 RCT
Retatrutide, a Triple Hormone Receptor Agonist, for Treatment of Obesity ↗ (external website)
DOI: 10.1056/NEJMoa2604169 ↗ (external website) - Phase 3 RCT DOI: 10.1016/S0140-6736(26)01861-1 ↗ (external website)
- Phase 3 RCT DOI: 10.1016/S0140-6736(26)00967-0 ↗ (external website)
-
Phase 2 RCT
Triple-Hormone-Receptor Agonist Retatrutide for Obesity - A Phase 2 Trial ↗ (external website)
DOI: 10.1056/NEJMoa2301972 ↗ (external website) - Discovery and phase 1 study DOI: 10.1016/j.cmet.2022.07.013 ↗ (external website)
- Phase 2 substudy DOI: 10.1038/s41591-024-03018-2 ↗ (external website)
- Registry Record
- Registry Record
- Registry Record
- Registry Record
-
FDA Safety Communication
FDA's concerns with unapproved GLP-1 drugs used for weight loss ↗ (external website)