Retatrutide (LY3437943): Research, Mechanism & Current Evidence
Investigational triple hormone receptor agonist studied in obesity and metabolic research.
Also known as LY3437943 · triple agonist · GLP-1/GIP/glucagon receptor agonist
What is Retatrutide?
Retatrutide is an experimental compound developed by Eli Lilly under the code LY3437943. It belongs to the same family as tirzepatide and semaglutide — synthetic molecules modelled on gut hormones the body releases after eating — but it is unusual in acting on three hormone receptors at once rather than one or two.
It has not been approved by any medicines regulator. As of this review it remains in phase 3 trials, so every result described below comes from a research setting rather than routine clinical use.
Status: Investigational. Not approved by the MHRA, FDA or EMA.
What is Retatrutide researched for?
Most published work looks at body weight and appetite in people living with obesity. Secondary questions include blood sugar control in type 2 diabetes, liver fat, blood pressure and cholesterol.
A separate strand of research examines whether adding a third pathway produces effects that dual-receptor compounds such as tirzepatide do not.
- Clinical trials show 17.5% weight loss at 24 weeks and 24.2% at 48 weeks.
- Continuous weight loss with no plateau at 48 weeks suggests greater long-term potential.
- Addresses obesity through appetite suppression, energy expenditure, and metabolic efficiency.
- HbA1c reductions up to 2.16% with 82% achieving target levels below 6.5%.
- Balanced glycemic control with minimal hypoglycemia risk.
- Marked improvements in sensitivity with potential for reduced exogenous insulin requirements.
- Non-HDL cholesterol reductions up to 26.9%, triglyceride reductions up to 40.6%.
- Consistent decreases in systolic and diastolic blood pressure across trials.
- Up to 82% reduction in liver fat with normalization in 90% of participants.
How does Retatrutide work?
Retatrutide works across three hormone pathways involved in metabolism — the GLP-1, GIP and glucagon receptors. The plain-English version is that it uses three different signals rather than one.
GLP-1 signalling slows the stomach and tells the brain you are full. GIP signalling affects how the body handles insulin and where fat is stored. Glucagon signalling is the interesting addition: rather than only reducing how much energy goes in, activating the glucagon receptor increases how much energy the body spends and how much fat the liver burns.
Reported targets: glucagon receptor, GLP-1 receptor, GIP receptor
What does the research show?
The most-cited result is a phase 2 trial published in the New England Journal of Medicine in 2023, in which participants receiving the highest dose lost around 24% of body weight at 48 weeks. Weight was still falling when the trial ended, which is why the figure is often described as not yet having reached a plateau.
The same programme reported reductions in liver fat and improvements in blood sugar markers. Gastrointestinal side effects — nausea, vomiting and diarrhoea — were the most common problem reported, consistent with other compounds in this class.
Limitations of the current evidence
Phase 2 trials are designed to find a dose and detect obvious safety signals, not to establish long-term outcomes. The larger phase 3 programme is what will determine whether the early figures hold.
Trial populations are selected and closely supervised, so results do not transfer directly to other groups. Longer-term questions — what happens to weight after stopping, and cardiovascular outcomes — do not yet have published answers.
References
Triple-Hormone-Receptor Agonist Retatrutide for Obesity - A Phase 2 Trial
Jastreboff AM, Kaplan LM, Frías JP, et al. · The New England journal of medicine · 2023
Landmark phase 2 RCT showing dose-dependent weight loss: 24.2% at 48 weeks with 12mg dose — the highest recorded for any obesity medication at the time. Weight reduction of ≥15% achieved in 83% of 12mg recipients.
Controlled clinical trial · PMID 37366315
Retatrutide, a GIP, GLP-1 and glucagon receptor agonist, for people with type 2 diabetes: a phase 2 trial
Rosenstock, J., et al. · The Lancet · 2023
Phase 2 trial in type 2 diabetes demonstrating clinically meaningful HbA1c reductions and robust weight loss of up to 16.9% at 36 weeks, with safety profile consistent with GLP-1 receptor agonists.
Controlled clinical trial
Sanyal AJ, Kaplan LM, Frias JP, et al. · Nature medicine · 2024
Dose-dependent liver fat reduction: 82.4% at 12mg dose. Normal liver fat (<5%) achieved in 86% of 12mg recipients vs 0% placebo at 24 weeks. Improvements linked to changes in body weight, abdominal fat, and insulin sensitivity.
Controlled clinical trial · PMID 38858523
Structural insights into the triple agonism at GLP-1R, GIPR and GCGR manifested by retatrutide
Li W, Zhou Q, Cong Z, et al. · Cell discovery · 2024
Cryo-EM structures reveal how retatrutide simultaneously activates GLP-1R, GIPR, and GCGR through distinct receptor-binding modes, explaining the molecular basis for its triple agonist activity and superior clinical efficacy.
PMID 39019866
TRIUMPH registrational clinical trials: Rationale and design Aronne, L.J., et al. Obesity
2025
Phase 3 TRIUMPH program design: four multicenter, randomized, double-blind studies assessing weekly retatrutide for obesity, obstructive sleep apnea, knee osteoarthritis, and weight management in cardiovascular disease populations.
Controlled clinical trial
Effects of retatrutide on body composition in people with type 2 diabetes: a phase 2 substudy
Rosenstock, J., et al. · The Lancet Diabetes & Endocrinology · 2025
Substudy demonstrating significant total body fat mass reduction with retatrutide vs placebo and dulaglutide. Proportion of lean mass loss to total weight loss was similar to other obesity treatments.
Controlled clinical trial
Coskun T, Wu Q, Schloot NC, et al. · The lancet. Diabetes & endocrinology · 2025
Controlled clinical trial · PMID 40609566
Giblin K, Kaplan LM, Somers VK, et al. · Diabetes, obesity & metabolism · 2026
PMID 41090431
Rosenstock J, Frias J, Jastreboff AM, et al. · Lancet (London, England) · 2023
Controlled clinical trial · PMID 37385280
Common questions
What does it mean that retatrutide is a triple agonist?
It activates three hormone receptors — GLP-1, GIP and glucagon — instead of one or two. Semaglutide acts on GLP-1 alone; tirzepatide acts on GLP-1 and GIP. The glucagon receptor is the addition that distinguishes retatrutide, and it is associated with increased energy expenditure rather than reduced intake.
What stage of research is retatrutide at?
Phase 3. Phase 2 results were published in 2023 and the larger confirmatory programme is ongoing. It is not an approved medicine anywhere.
How does the published weight-loss figure compare with other compounds?
The phase 2 figure of roughly 24% at 48 weeks is higher than the headline figures reported for tirzepatide (around 21% at 72 weeks in SURMOUNT-1) or semaglutide (around 15% at 68 weeks in STEP-1). These come from separate trials with different designs and populations, so they are not a direct head-to-head comparison.