Retatrutide – Research Peptide

What retatrutide is

Retatrutide (development code LY3437943) is a single synthetic peptide with agonist activity at three receptors: the glucose-dependent insulinotropic polypeptide (GIP) receptor, the glucagon-like peptide-1 (GLP-1) receptor, and the glucagon receptor^[1]. The third arm is what distinguishes it from the dual agonists. It is being developed by Eli Lilly and Company, which funded both phase 2 trials cited on this page^[1][2].

Retatrutide is investigational. It is not approved by the FDA, the EMA, or any other regulator, for any indication, anywhere. The Phase 3 programme has now reported. Lilly announced TRIUMPH-1 results on 21 May 2026 and TRIUMPH-2 and TRIUMPH-3 on 23 July 2026, across five Phase 3 studies, with a Biologics License Application planned for the first quarter of 2027. Almost all of that exists as sponsor announcements and conference presentations rather than peer-reviewed papers. The trial write-ups below are Phase 2, because Phase 2 is still where the published, peer-reviewed record largely sits. Everything below should be read against that distinction.

Structure and identity — the gap unverified

What is established, from the peer-reviewed literature rather than from a chemical database, is the pharmacology: a single peptide, once-weekly subcutaneous administration, agonism at GIP, GLP-1 and glucagon receptors^[1][2].

Every batch we supply is assayed by an independent laboratory using HPLC-UV-MS: mass spectrum against an authentic reference standard for identity, peak area against total chromatogram area for chromatographic purity, and total peptide mass against the stated label claim. Measured values for lot fghe8m6 are published in the specification block above. Certificates for other lots are posted as they are released.

Where the evidence stands

This is the section most vendors skip. It is the most important one on the page.

The phase 2 obesity trial human

Jastreboff et al., New England Journal of Medicine, 2023. A phase 2, double-blind, randomised, placebo-controlled trial in 338 adults with a BMI of 30 or higher, or 27 to under 30 plus at least one weight-related condition. Participants were randomised across six retatrutide dose regimens (1, 4, 8 and 12 mg, with different starting doses) or placebo, once weekly for 48 weeks^[1].

Least-squares mean percentage change in body weight at 48 weeks:

• 1 mg: −8.7%
• 4 mg (combined): −17.1%
• 8 mg (combined): −22.8%
• 12 mg: −24.2%
• Placebo: −2.1%

At 48 weeks, a reduction of 15% or more had occurred in 83% of the 12 mg arm versus 2% on placebo^[1]. These are phase 2 numbers in 338 people. They are not a phase 3 result, and they are not an approval.

The phase 2 diabetes trial human

Rosenstock et al., Lancet, 2023. A randomised, double-blind, double-dummy, placebo- and active-comparator-controlled phase 2 trial across 42 US centres, in 281 adults with type 2 diabetes. Mean HbA_1c change at 24 weeks ranged from −0.43% (0.5 mg) to −2.02% (12 mg) versus −0.01% with placebo and −1.41% with the active comparator. Bodyweight change at 36 weeks ranged from −3.19% (0.5 mg) to −16.94% (12 mg), versus −3.00% with placebo^[2].

Note the trial’s own limits: 237 of 281 participants (84%) completed the study, and only 222 (79%) completed study treatment^[2]. One in five people did not finish the drug.

Liver fat substudy human

Sanyal et al., Nature Medicine, 2024. A randomised, double-blind, placebo-controlled substudy of the phase 2 obesity trial, in 98 participants with metabolic dysfunction-associated steatotic liver disease and at least 10% liver fat. Mean relative change in liver fat at 24 weeks was −42.9% (1 mg), −57.0% (4 mg), −81.4% (8 mg), −82.4% (12 mg) and +0.3% (placebo)^[3]. Liver-fat changes were significantly related to changes in body weight and abdominal fat — that is, the authors did not establish an effect independent of weight change^[3].

Mechanism at the receptor in vitro

Retatrutide’s distinguishing feature is the glucagon receptor arm added on top of GIP and GLP-1 agonism^[1]. Glucagon receptor agonism is a double-edged mechanism: it is associated with increased energy expenditure, and it is also the pathway most plausibly behind the heart-rate signal described below. This is receptor pharmacology characterised in assay systems. It is not a statement about anything happening in a person.

Adverse events and safety signals

Dose-dependent heart rate increases human

Gastrointestinal events human

The most common adverse events in the obesity trial were gastrointestinal: dose-related, mostly mild to moderate, and partially mitigated by a lower starting dose (2 mg rather than 4 mg)^[1]. “Partially” is the operative word — the trial design itself concedes the escalation schedule does not eliminate the problem.

In the diabetes trial, mild-to-moderate gastrointestinal adverse events — nausea, diarrhoea, vomiting, constipation — were reported in 67 of 190 participants across the retatrutide arms (35%), ranging from 13% in the 0.5 mg group to 50% in the 8 mg fast-escalation group, versus 13% on placebo^[2].

What was not observed human

In the diabetes trial, there were no reports of severe hypoglycaemia and no deaths during the study^[2]. That is worth stating plainly — but a 281-person, 36-week trial is not sized to find rare events, and the absence of a signal in a small trial is not evidence of safety.

Limitations of the literature

The peer-reviewed evidence base is thin, and it is still Phase 2. Three published trials, n=338, n=281 and n=98, all in the same programme, all funded by Eli Lilly and Company, with Lilly employees as co-authors on all three^[1][2][3]. Phase 2 trials exist to select doses and generate hypotheses. They are not confirmatory.

The liver-fat and diabetes results share a population with the obesity trial. The Nature Medicine substudy is a subset of the phase 2 obesity trial participants, not an independent cohort^[3]. Three papers do not mean three independent replications.

The chemical identity gap is not cosmetic. A compound with no public chemical database record is a compound whose identity you cannot independently verify against anything. For a molecule this new, that is not surprising. It is still a real limitation, and it belongs in the same paragraph as the efficacy numbers.

Regulatory and anti-doping status

Retatrutide has not been approved by the FDA, the EMA, or any other regulatory authority, for any indication, in any jurisdiction. It is an investigational compound whose Phase 3 programme has reported topline results but whose peer-reviewed Phase 3 record remains thin^[4].

Because no regulator anywhere has approved it for human therapeutic use, it falls under WADA category S0, Non-Approved Substances — prohibited at all times, in and out of competition. That is not a technicality, and it is not conditional on retatrutide appearing by name on any list. Anti-doping lists change annually and by governing body, and investigational compounds can be captured by catch-all provisions covering substances with no current regulatory approval. If you compete under any tested organisation, the only reliable source is that organisation’s current prohibited list — not this page, and not any vendor’s.

What we don’t know

• Independent database confirmation of the molecular formula and mass. Suppliers consistently publish C221H342N46O68 at 4731.33 g/mol under CAS 2381089-83-2, and those figures agree across sources, but supplier documentation is not the same thing as a public chemical-database record and we distinguish between the two.
• What the dose-dependent heart-rate increase means for cardiovascular outcomes. No published trial can answer that^[1].
• Whether the Phase 3 results hold up under peer review. The reported effect sizes are large and, unusually, larger than Phase 2 rather than smaller, but a topline sponsor announcement is not the same evidentiary object as a published trial and we do not treat it as one.
• Anything about long-term safety. The longest published exposure is 48 weeks^[1].
• Per-kilogram dosing in animal models does not scale to humans, and nothing on this page should be read as implying that it does.

We supply this compound for laboratory research. The data are genuinely striking, and retatrutide has now cleared the stage where most compounds fail. What it has not cleared is publication, peer review, or a regulator.