Retatrutide
An investigational, once-weekly triple receptor agonist engineered to activate GIP, GLP-1 and glucagon receptors within a single peptide molecule.
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Retatrutide
For laboratory research only. Not for human consumption.
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What is Retatrutide?
Retatrutide, also known by the development code LY3437943, is a long-acting peptide designed to combine agonist activity at three metabolically relevant receptors: the glucose-dependent insulinotropic polypeptide receptor (GIPR), the glucagon-like peptide-1 receptor (GLP-1R) and the glucagon receptor (GCGR).
The scientific rationale is broader than appetite modulation alone. GLP-1 and GIP receptor signalling can influence satiety, food intake, insulin secretion and glycaemic regulation, while glucagon receptor activity is being investigated for its potential contribution to energy expenditure and lipid metabolism. Retatrutide therefore represents a multi-pathway approach to metabolic research rather than a conventional single-receptor incretin strategy.
A coordinated triple-agonist design
GLP-1 receptor
GLP-1 receptor activation is associated with increased satiety, reduced energy intake, glucose-dependent insulin secretion and delayed gastric emptying. It provides the established incretin foundation of the molecule.
GIP receptor
GIP receptor agonism may complement GLP-1 signalling through effects on insulin secretion, nutrient handling and adipose-tissue biology. Its contribution is evaluated as part of the combined receptor profile.
Glucagon receptor
Glucagon receptor activation is being studied for its capacity to increase energy expenditure and influence hepatic lipid metabolism, potentially extending the effect beyond appetite suppression.
How the receptor profile differs
| Compound | GLP-1R | GIPR | GCGR |
|---|---|---|---|
| Semaglutide | ✓ | — | — |
| Tirzepatide | ✓ | ✓ | — |
| Retatrutide | ✓ | ✓ | ✓ |
From proof of concept to the TRIUMPH programme
Phase 1 First-in-human and early multiple-dose studies
The initial clinical programme evaluated LY3437943 in early-phase studies designed to characterise safety, tolerability, pharmacokinetics and pharmacodynamic effects. The first-in-human single-ascending-dose work supported a prolonged exposure profile compatible with weekly administration. A subsequent early-phase multiple-dose study in people with type 2 diabetes investigated stepwise dose escalation and reported dose-dependent reductions in glucose and body weight.
These studies did not carry a public brand name comparable with TRIUMPH. They are generally identified by the development code LY3437943, their study protocol and their publication titles.
Phase 2 Obesity trial — NCT04881760
The pivotal phase 2 obesity study was a randomised, double-blind, placebo-controlled trial involving 338 adults with obesity or overweight plus at least one weight-related condition. Participants were assigned to placebo or once-weekly retatrutide target doses of 1 mg, 4 mg, 8 mg or 12 mg for 48 weeks. Several higher-dose groups used lower starting doses and gradual escalation.
At 48 weeks, mean body-weight change was approximately −8.7% with 1 mg, −17.1% with combined 4 mg groups, −22.8% with combined 8 mg groups and −24.2% with 12 mg, compared with −2.1% with placebo. The trial established a clear dose-response signal and provided the basis for phase 3 development.
Phase 3 TRIUMPH clinical programme
TRIUMPH is the phase 3 development programme evaluating retatrutide across obesity and related cardiometabolic conditions. The programme includes general obesity populations as well as dedicated cohorts involving type 2 diabetes, cardiovascular disease, knee osteoarthritis, obstructive sleep apnoea and longer-term cardiovascular and renal outcomes.
As of 2026, retatrutide remains investigational and is not approved for public use. Published journal articles and regulatory review will remain the appropriate sources for final interpretation of phase 3 findings.
Study regimens and dose escalation
Phase 2 obesity study arms
| Target dose | Starting strategy used in the study | Frequency | Treatment period |
|---|---|---|---|
| 1 mg | 1 mg from initiation | Once weekly | 48 weeks |
| 4 mg | Either 2 mg lead-in or direct 4 mg arm | Once weekly | 48 weeks |
| 8 mg | 2 mg or 4 mg starting dose with escalation | Once weekly | 48 weeks |
| 12 mg | 2 mg starting dose with stepwise escalation | Once weekly | 48 weeks |
Illustrative escalation pattern used for higher target doses
Dose escalation was incorporated into higher-dose study arms to improve tolerability, particularly during the early treatment period when gastrointestinal adverse events were most frequently reported.
What the published studies reported
Mean weight change
Observed at 48 weeks in the 12 mg phase 2 group, compared with −2.1% in the placebo group.
8 mg groups
Mean change at 48 weeks across the combined 8 mg study groups.
4 mg groups
Mean change at 48 weeks across the combined 4 mg study groups.
TRIUMPH-1 topline result
Lilly reported this mean reduction at 80 weeks for the 12 mg estimand in its 2026 phase 3 topline announcement. Full peer-reviewed interpretation remains important.
Beyond total body-weight change, the clinical programme has examined waist circumference, cardiometabolic markers, glycaemic outcomes, liver fat, osteoarthritis symptoms, sleep-apnoea severity and cardiovascular or renal outcomes. The strength of evidence differs by endpoint: phase 2 obesity data are peer reviewed, whereas some phase 3 findings were initially released as sponsor-reported topline results.
Commonly reported adverse events
Nausea, diarrhoea, vomiting, constipation and reduced appetite.
Long-acting peptide engineering
Retatrutide is a synthetic peptide linked to a fatty diacid moiety. This design promotes albumin binding and extends systemic exposure. Early clinical studies reported pharmacokinetic properties compatible with once-weekly dosing, while the single-dose first-in-human investigation observed body-weight effects that persisted for several weeks after administration.
Phonyx portfolio formats
Evidence behind the key claims
Frequently asked questions
Is retatrutide an approved medicine?
No. Retatrutide remains an investigational compound and is not approved for public use as of 2026.
Why is it described as a triple agonist?
Because one peptide molecule activates the GIP, GLP-1 and glucagon receptors.
What doses were evaluated in the phase 2 obesity trial?
Target doses of 1 mg, 4 mg, 8 mg and 12 mg administered once weekly were studied, with escalation strategies used in several higher-dose groups.
Are the 20 mg and 30 mg formats clinical doses?
No. They are total vial contents planned for the Phonyx research catalogue and should not be confused with the weekly target doses used in clinical trials.
What is the TRIUMPH programme?
TRIUMPH is Lilly's phase 3 clinical development programme for retatrutide across obesity and associated cardiometabolic conditions.
Why are clinical-trial dosing schedules shown here?
They are included to document the design of published research. They are not instructions for self-administration or medical advice.
Research Disclaimer
This compound is presented exclusively for laboratory and scientific research. It is not intended for human consumption, self-administration, diagnostic use, treatment, cure or prevention of disease. Information describing clinical studies is provided for documentary and educational context only and must not be interpreted as medical advice, a dosing recommendation or instructions for use. Retatrutide remains investigational and has not been approved for public use.