A tier · strong
Retatrutide has now read out four positive phase 3 TRIUMPH trials with the largest weight reductions ever reported for a pharmacological agent, but it remains unapproved with no cardiovascular outcomes data and an FDA filing not expected until Q1 2027.
retatrutide
Retatrutide is an investigational once-weekly triple agonist at GIP, GLP-1 and glucagon receptors that has completed multiple phase 3 obesity trials with mean weight reductions of roughly 26% to 30% at the highest doses. It is not approved anywhere; Eli Lilly has stated it will file for FDA approval in the first quarter of 2027, and no cardiovascular or mortality outcome data have been published.
the explanation
Retatrutide acts on three hormone receptors at once, including one that raises how many calories the body burns, and in trials it produced the largest weight loss of any drug so far, around 25 to 30 percent. It is still experimental, has not been approved anywhere, and roughly one in six people at the highest dose stopped taking it because of side effects.
regulatory status
Investigational — not approved (as of July 2026)
No marketing authorisation in any jurisdiction; Eli Lilly announced in July 2026 that it will submit an FDA application in Q1 2027 following positive TRIUMPH-1, -2, -3 and -4 readouts.
how it works · proposed mechanism
Retatrutide adds glucagon receptor agonism to the established GIP/GLP-1 incretin backbone.
Three receptors at once
Retatrutide activates GIP, GLP-1 and glucagon receptors from a single molecule, combining appetite suppression with a catabolic energy-expenditure arm. This is the mechanistic basis for weight reductions exceeding those of dual agonists.
Glucagon burns liver fat
Glucagon receptor agonism in hepatocytes increases fatty acid oxidation and reduces hepatic lipid content. A phase 2a MASLD trial reported near-complete normalisation of liver fat in a majority of participants at higher doses.
Raises energy expenditure
Unlike pure incretin agonists which work almost entirely by reducing intake, glucagon signalling raises resting metabolic rate. The magnitude of this contribution in humans has not been directly quantified in the phase 3 programme.
Glucagon's metabolic cost
Glucagon receptor agonism can raise hepatic glucose output and heart rate, effects that must be offset by the incretin arms. Dose-dependent heart-rate increases and transient glycaemic effects have been reported and remain a monitoring focus.
what’s reported
evidence shape
5 sourcesThe composition of the cited literature by study type. This describes the shape of the evidence, not its quality — and it does not by itself set the grade.
⚠ the catch
Tolerability degrades sharply with dose: discontinuation for adverse events reached 11.3% at 12 mg in TRIUMPH-1 and 18.2% at 12 mg in TRIUMPH-4, versus roughly 4% on placebo, with nausea affecting up to 43% of participants. Beyond that, the entire evidence base is currently company-reported top-line and short-term, with no cardiovascular outcome trial and no approval before 2027 at the earliest.
key published findings
- TRIUMPH-1 (n=2,339, 80 weeks) reported mean weight reductions of 19.0%, 25.9% and 28.3% at 4 mg, 9 mg and 12 mg; a 532-participant extension with baseline BMI ≥35 reached 30.3% mean loss at 104 weeks on 12 mg.
- TRIUMPH-4 (n=445, 68 weeks) in participants with knee osteoarthritis reported 26.4% and 28.7% weight loss at 9 mg and 12 mg versus 2.1% on placebo, with WOMAC pain reduction up to 75.8%.
- TRIUMPH-2 (n=1,152, 80 weeks) in type 2 diabetes reported 12.7%, 19.1% and 20.8% weight loss at 4/9/12 mg versus 4.0% on placebo, with HbA1c reductions of 1.4–1.6% versus 0.2%.
- TRIUMPH-3 (n=1,949, 80 weeks) in severe obesity with cardiovascular disease reported 21.6% and 22.6% weight loss at 9 mg and 12 mg versus 3.2% on placebo.
- TRIUMPH-4 reported nausea in 38.1–43.2% and diarrhoea in 33.1–34.7% of retatrutide participants versus 10.7% and 13.4% on placebo, with AE discontinuation of 12.2% and 18.2% versus 4.0%.
limitations of the evidence
- Most phase 3 results are available only as company press releases and conference presentations; full peer-reviewed publications with complete safety datasets are not yet available for TRIUMPH-2, -3 and -4.
- No cardiovascular outcomes trial has reported, so the effect of chronic triple agonism on hard endpoints is entirely unknown.
- Long-term consequences of sustained glucagon receptor agonism, including effects on heart rate, lean mass and hepatic glucose handling, are not characterised beyond two years.
identity
| full name | Retatrutide (LY3437943, GIP/GLP-1/glucagon triple receptor agonist) |
| category | Metabolic |
| modality | peptide |
| formula | C221H342N46O68 |
| cas | 2381089-83-2 |
| half-life | ~6 days (phase 1 estimate) |
| sequence | Y-Aib-QGTFTSDYSIΨLDKK(C20 diacid conjugate)AQ-Aib-AFIEYLLEGGPSSGAPPPS-NH2 (39 residues; Aib substitutions and lipidated Lys17) |
laboratory handling
| storage | Lyophilised material is typically stored at −20 °C in desiccated, light-protected vials; reconstituted solutions are generally held at 2–8 °C for short-term laboratory use or aliquoted at −80 °C to minimise freeze-thaw exposure. |
| solubility | Laboratory stocks are commonly reconstituted in bacteriostatic or sterile water; DMSO is used for in vitro assay preparations. |
| co-studied with | No combination regimens have been tested in registrational trials; retatrutide is being developed as monotherapy. |
Handling information describes laboratory practice for a research reagent. It is not a preparation guide for use in humans.
the receipts
5 citedEli Lilly and Company · 2025 · official
NEJM · 2023 · peer-reviewed
Nature Medicine · 2024 · peer-reviewed
AJMC · 2026 · review
PR Newswire / Eli Lilly · 2026 · press release
Sources marked tertiary or press release are the weakest citations on this page.
others in Metabolic