Retatrutide in 2026: The TRIUMPH Phase 3 Program and What "Investigational" Means

• ·Retatrutide (LY3437943) is a single peptide that activates three receptors: GIP, GLP-1 and glucagon.[1]
• ·Eli Lilly reported TRIUMPH-1 phase 3 results in May 2026 and TRIUMPH-2 and TRIUMPH-3 results in July 2026, and said all three met their primary endpoints.[3][4] These are company-reported topline data, not peer-reviewed publications.
• ·Retatrutide is not FDA-approved. It is an investigational compound, and the FDA has named it in warning letters to sellers marketing it for human use.[5][6]
• ·Research-grade retatrutide is a chemical reagent for in vitro and laboratory work. It is not Lilly's clinical product and is not for human use.

Retatrutide is a 39-amino-acid peptide built on a GIP backbone and modified with a C20 fatty diacid moiety that binds albumin and extends its half-life.[1] In receptor assays, Coskun and colleagues reported that it activates the human GIP receptor with greater potency than native GIP, and the GLP-1 and glucagon receptors with lower potency than their native ligands. The paper summarizes the result as balanced glucagon and GLP-1 receptor activity with more GIP receptor activity.[1]

That profile, weighted toward GIP with substantial GLP-1 and glucagon receptor activity alongside, is what distinguishes it from mono-agonists such as semaglutide and dual agonists such as tirzepatide. Our post on incretin receptor pharmacology compares the three classes, and retatrutide vs tirzepatide takes the dual-against-triple question on its own.

Research Material

Amino Acid Sequence

Chemical Structure

• ·2022. Discovery and preclinical pharmacology published in Cell Metabolism.[1]
• ·2022. Phase 1b trial in type 2 diabetes published in The Lancet.[2]
• ·2023. Phase 2 obesity trial (NCT04881760) published in the New England Journal of Medicine.[7]
• ·2023. Phase 2 type 2 diabetes trial published in The Lancet.[8]
• ·2025. Rationale and design of the TRIUMPH registrational trials published online in October (Diabetes, Obesity and Metabolism, January 2026 issue).[9]
• ·May 2026. TRIUMPH-1 topline results announced (NCT05929066).[3]
• ·July 2026. TRIUMPH-2 and TRIUMPH-3 topline results announced.[4]

Lilly's press releases describe the phase 3 program as follows. Every figure in this section is company-reported topline data, not yet a peer-reviewed publication, and the weight-change percentages are the efficacy-estimand results Lilly led with.

• ·TRIUMPH-1. Lilly reported randomizing 2,339 adults with obesity or overweight and at least one weight-related condition, without diabetes, for 80 weeks. Mean body-weight reductions were 19.0%, 25.9% and 28.3% in the 4 mg, 9 mg and 12 mg arms, against 2.2% on placebo (17.6%, 23.7% and 25.0% against 3.9% under the treatment-regimen estimand). Discontinuation due to adverse events was 4.1%, 6.9% and 11.3% in those arms, against 4.9% on placebo. The most common adverse events were gastrointestinal: nausea, diarrhea, constipation and vomiting.[3]
• ·TRIUMPH-2 studied adults with type 2 diabetes and obesity or overweight. TRIUMPH-3 studied adults with severe obesity (BMI of 35 or more) and established cardiovascular disease. Lilly reported that both 80-week trials met their primary endpoints.[4]

For researchers, the discontinuation pattern is as informative as the efficacy figures. In TRIUMPH-1, discontinuation due to adverse events rose with dose, from below the placebo rate in the 4 mg arm to more than twice it in the 12 mg arm.[3] That gives a clinical reference point for the tolerability limits of combined GLP-1 and glucagon receptor activation.

The pattern should be read trial by trial until full results are published: in the TRIUMPH-2 release the rates did not rise in step with dose.[4]

• ·Glucagon receptor contribution. How much of retatrutide's effect on energy expenditure and liver fat comes from glucagon receptor agonism, and how does that interact with its glycemic effects?
• ·Receptor bias and trafficking. Tirzepatide shows biased signaling at the GLP-1 receptor.[10] Whether retatrutide shows a comparable pattern is a live in vitro question.
• ·Lean mass. Body-composition analyses across the TRIUMPH program will be of interest once they are peer-reviewed.

Retatrutide is investigational. It has no approved indication, is not on any compounding list, and cannot lawfully be marketed for human use. In warning letters dated 31 March 2026, the FDA cited retatrutide among products online sellers were offering for human use despite "research use only" labeling, including under coded names: one seller listed it as "GLP-1-R peptide", another as "GLP-3 RT".[5][6]

Labs should expect a research supplier to identify the compound by its proper name and sequence, and to provide batch-specific analytical data.

Each retatrutide lot is tested by Janoshik Analytical before sale, and the certificate is published as the laboratory reported it, verifiable on Janoshik's own site. The current certificates are below, with a switch for each strength. Full reports for every lot are on our certificates of analysis page.

Published Certificate

Select strength

10mg20mg40mg50mg

Batch

RETA-CA-26E-01

Purity (HPLC)

99.637%

Measured content

11.76 mglabeled 10 mg

Laboratory

Janoshik

Verify on the lab’s own databaseAll published certificates

Available at Eppix Labs

Retatrutide (Triple Agonist)

10mg · 20mg · 40mg · 50mg

Every batch tested by an independent laboratory, with the certificate published before sale.

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