Retatrutide Science: The Triple GLP-1/GIP/Glucagon Agonist Mechanism

Retatrutide's headline number is real and its evidence tier is not what most sources say. 24.2% average weight loss comes from a phase 2 trial of 338 people over 48 weeks. No phase 3 result has been published, including by us.

Retatrutide sits in the weight loss and metabolic peptides category as its most-tested and least-evidenced compound: 1,150 independent lab tests against one published trial. For per-injection volume there is a retatrutide calculator. What follows traces every circulating figure back to its source, or reports that it has none.

Where does retatrutide's 24.2% figure actually come from?

Retatrutide's 24.2% average weight loss comes from Jastreboff et al., "Triple-Hormone-Receptor Agonist Retatrutide for Obesity — A Phase 2 Trial," New England Journal of Medicine 2023;389(6):514–526 (PMID 37366315). It is a phase 2 result: n=338, 48 weeks, 12 mg dose, double-blind and placebo-controlled. The figure is correctly reported; the phase attached to it usually is not. As of 11 August 2026, PubMed contains no phase 3 retatrutide results paper.

At least 15% weight loss was achieved by 60–83% of participants across doses, versus 2% on placebo. Adverse events were dose-related and gastrointestinal, mostly mild to moderate. The discontinuation rate is not reported in the abstract, and we are not quoting one.

A search of the New England Journal of Medicine returns four retatrutide records, all from 2023. That is a genuinely striking result and it is why retatrutide has the profile it does. It is also 338 people over 48 weeks — a phase 2 trial doing what phase 2 trials do, which is generate a hypothesis worth testing properly.

What is retatrutide, and what does glucagon receptor agonism add?

Retatrutide is a triple agonist at the GIP, GLP-1 and glucagon receptors, molecular weight 4,731.0 g/mol, formula C₂₂₁H₃₄₂N₄₆O₆₈, development code LY3437943 (Eli Lilly). Adding glucagon receptor agonism to the GIP/GLP-1 combination that tirzepatide uses is intended to raise energy expenditure alongside appetite suppression — a different lever from eating less. Its CAS number is commonly quoted as 2381089-83-2, which we could not verify against a chemical registry.

PubChem's record does not expose a CAS number for retatrutide, and the number circulating on vendor pages comes from secondary sources. That is a small thing on its own and a notable thing in aggregate: this is a compound where much of what is quoted as specification traces to nowhere authoritative.

The mass matters for a practical reason. At 4,731.0 g/mol retatrutide sits 82 daltons below tirzepatide at 4,813.0 — a gap a mass spectrometer resolves instantly and an HPLC purity figure does not address at all.

Has the TRIUMPH phase 3 programme published anything?

TRIUMPH has published a design paper and no results. Giblin et al. (Diabetes, Obesity and Metabolism, January 2026, PMID 41090431) describe four registrational trials and more than 5,800 participants: TRIUMPH-1 and TRIUMPH-2 as weight-management basket trials with nested sleep apnoea and osteoarthritis protocols, TRIUMPH-3 in obesity with cardiovascular disease, and TRIUMPH-4 in knee osteoarthritis. Primary endpoints are percent body weight change, apnoea-hypopnoea index, and WOMAC pain.

Two further trials are registered. A cardiovascular and kidney outcomes trial, NCT06383390, is active and not recruiting. A head-to-head against tirzepatide, NCT06662383, is likewise active and not recruiting.

None of these has published results. For the programme trial by trial, see the TRIUMPH programme trial by trial.

Where do the 28% and 30.3% figures come from?

The 28% at 80 weeks figure traces to press reporting of a company statement in May 2026, not to a trial publication, and we could not verify it against a primary source. The 30.3% at 104 weeks figure has no source we could find at all. This site's own retatrutide page stated that 24.2% came from "Phase 3 TRIUMPH-1" over 80 weeks, with 30.3% at 104 weeks. Both figures are wrong and we are correcting them.

The pattern is worth naming, because it is how a phase 2 number becomes a phase 3 number in public. A company statement is reported in the press, the press figure is quoted without its provenance, the duration drifts, and within a few links the result is attributed to a trial that has published nothing. Every step is ordinary. The output is a number no reader can trace.

Is retatrutide approved anywhere, and can it be legally compounded?

Retatrutide is not approved anywhere we could verify. FDA's drug application database returns no match, and retatrutide is absent from FDA's novel approvals lists for 2025 (46 drugs) and 2026 (30 drugs, current through 5 August 2026). It also cannot be legally compounded: retatrutide has never been approved, so it has never been in shortage, so no compounding pathway has ever existed for it. The shortage-based route that briefly legitimised compounded semaglutide and tirzepatide never applied here.

Retatrutide does not appear on FDA's compounding lists. We enumerated both tables on the page current 22 April 2026 — no GLP-1, GIP, glucagon or amylin agonist is on either. That absence carries no permission whatsoever. Retatrutide sold outside a clinical trial or expanded access programme is an unapproved new drug, full stop.

FDA's published position on this class is directly applicable: the agency "has warned companies that have illegally sold unapproved drugs... falsely labeled 'for research purposes' or 'not for human consumption.' These products have been sold directly to consumers for human use."

One change worth knowing: ClinicalTrials.gov now carries NCT07629401, "Pre-approval Expanded Access of Retatrutide," with status AVAILABLE. Expanded access — sometimes called compassionate use — is a route for patients to receive an investigational drug outside a trial. It is not approval, and it operates through physicians and the sponsor, not through vendors. See do you need a prescription for retatrutide and compounding pharmacy versus research peptide.

Is retatrutide prohibited in sport?

Retatrutide is not named on the WADA 2026 Prohibited List, and no GLP-1 class entry exists. But the S0 catch-all prohibits substances "with no current approval by any governmental regulatory health authority for human therapeutic use," expressly including "drugs under pre-clinical or clinical development." Retatrutide holds no approval anywhere, so on the plain text S0 applies. That is our reading rather than a published WADA ruling, and an athlete should seek a determination rather than rely on either interpretation.

This is where retatrutide differs from tirzepatide. Tirzepatide is an approved drug, which takes it outside S0 entirely; retatrutide is not, which arguably brings it inside. Two compounds in the same mechanistic family land on opposite sides of the same rule for a purely regulatory reason.

What has been published about retatrutide sold outside trials?

Three 2026 publications bear on retatrutide outside the clinic, and we could not retrieve the contents of any of them. A BMJ fact-check dated 9 July 2026 asks whether a man died after taking the unapproved weight loss jab (PMID 42425580); a BMJ news item dated 7 August 2026 covers the expanded access opening (PMID 42567543); and Piatkowski, Craven, Cornell & Ferris report on the composition and labelling accuracy of products sold as retatrutide in Australia (Drug and Alcohol Review, September 2026).

We verified the BMJ titles and DOIs and could not access the text, so we are not characterising what either concludes. Both are worth reading directly.

The Australian paper is the one most relevant to this platform: "Composition and Labelling Accuracy of Products Sold as Retatrutide in Australia," DOI 10.1111/dar.70231 (PMID 42559975). We verified the citation and could not obtain the abstract. It is the closest peer-reviewed analogue to what we do here, and anyone buying retatrutide should read it. For the adverse-event picture as reported so far, see retatrutide side effects.

What do 1,150 independent lab tests show — and what can they not show?

The Purity Index records retatrutide at 99.67% average across 1,150 independent tests (verified August 2026) — the largest test dataset on this platform — from Janoshik, Freedom Diagnostics, Bioviridian, Kovera and ILS, across 230 shops selling. Individual results run 99.52% to 99.98%, and quantity variance runs −4% to +22.5%, with most within ±5%. What those tests cannot show is efficacy, dosing, long-term safety, or how a phase 2 result will hold up in phase 3.

Stop and consider that number. Eleven hundred and fifty independent lab tests of a drug that has never been approved and has no published phase 3 result. The supply chain for retatrutide is better characterised than the drug is.

That points in an uncomfortable direction: purity data has become a substitute for clinical evidence in how this compound is discussed. High-quality manufacture of a molecule with 338 people of phase 2 data behind it is high-quality manufacture of a molecule with 338 people of data behind it.

Purity and quantity answer different questions, and conflating them is the most common reading error on a certificate of analysis — see why 10 mg isn't 10 mg.

Retatrutide price data shows 15 shops in stock, median $8.00/mg, lowest $2.33/mg on a 40 mg vial (verified 31 July 2026), across 53 compared offers with vial prices from $24.99 to $500.00. By size: 5–10 mg runs a median $11.50/mg, 12–24 mg $8.23/mg, 30–65 mg $6.67/mg. Those figures exclude shipping, taxes and customs, coupon codes, bulk tiers, multi-vial kits and account-gated pricing.

Peptigrity's platform currently tracks 530 shops and 11,852 independent lab tests across 118 peptides, with 1,283 community reviews (verified August 2026), and trust scores weight community reviews and independently verified HPLC purity equally at 50% each. Compare vendors on the retatrutide compound page, search individual results in the lab test database, and see where to buy retatrutide.

Which retatrutide claims survive the evidence?

Two of the ten claims commonly made about retatrutide are straightforwardly true: the triple-agonist mechanism, and the 24.2% figure provided it is labelled phase 2. A third is true with a caveat — expanded access is genuinely available under NCT07629401, through a physician rather than a vendor. The rest are false, unsourced, unverified, unknown or untested, and on sport, arguably prohibited under S0.

How does a phase 2 result compare with phase 3 rivals?

Retatrutide's −24.2% leads the field on paper and is the only phase 2 entry in it. Tirzepatide reached −20.9% in SURMOUNT-1 (n=2,539, 72 weeks), CagriSema −20.4% in REDEFINE-1 (n=3,417), mazdutide −16.65% in GLORY-2, semaglutide −14.9% in STEP-1 (n=1,961) and survodutide −13.0% in SYNCHRONIZE-1 — every one of them a phase 3 trial enrolling between 461 and 3,417 participants. Cross-trial comparison is not head-to-head in any case, and phase 2 estimates routinely shrink.

Phase 2 results routinely shrink in phase 3. Populations broaden, adherence falls, dropout rises, and the estimand changes. Retatrutide may well hold up — but it has not yet been asked to, at scale, with results anyone outside the sponsor can read. See our retatrutide versus survodutide versus mazdutide comparison.

The trial that would settle this

Nothing about retatrutide's efficacy is settled beyond 338 participants over 48 weeks. Phase 3 weight-loss results are registered and unpublished, the cardiovascular and kidney outcomes trial (NCT06383390) and the head-to-head against tirzepatide (NCT06662383) are active and not recruiting, and durability beyond 48 weeks is unpublished. The most consequential gap is the one that sounds smallest: the discontinuation rate at effective doses is not reported in the phase 2 abstract.

That last row deserves more attention than it gets. Glucagon receptor agonism adds nausea and vomiting risk on top of an already emetogenic class, and the phase 2 abstract does not tell us how many people left the trial because of it. Every drug in this class shows its tolerability problem at scale, not in a 338-person study.

Frequently Asked Questions

Is the 24.2% weight loss figure real?

Yes, and it comes from a phase 2 trial: 338 participants, 48 weeks, 12 mg dose, published in the New England Journal of Medicine in 2023. It is not a phase 3 result, and phase 3 results for retatrutide have not been published.

What about the 28% figure?

It traces to press reporting of a company statement in May 2026, not to a trial publication. We could not verify it against a primary source and are not treating it as established.

Is retatrutide approved?

No. It does not appear in FDA's drug application database or on FDA's novel approvals lists for 2025 or 2026. A pre-approval expanded access programme is now listed as available (NCT07629401), which operates through physicians and the sponsor rather than through vendors.

Can it be legally compounded?

No. The compounding route that briefly applied to semaglutide and tirzepatide depended on those drugs being approved and in shortage. Retatrutide has never been approved, so no such route has ever existed for it.

Is it banned in sport?

It is not named on the WADA 2026 Prohibited List, but the S0 catch-all prohibits substances with no approval from any governmental health authority, expressly including drugs in clinical development. On the plain text that captures retatrutide. That is our reading, not a published ruling — seek a determination.

Does the purity data mean it is safe?

No. The 1,150 lab tests on this platform establish that vendors are broadly selling the correct molecule. They say nothing about efficacy, dosing, long-term safety or how a phase 2 result will hold up in phase 3 — all of which remain open.

Where this sits

Retatrutide is the most striking dataset in obesity medicine and the least complete one, and the gap between those two facts is where the confusion lives. The phase 2 result is remarkable — 24.2% at 48 weeks, with 60% to 83% of participants losing at least 15% — and nobody should dismiss it. It is also 338 people, with nothing published three years later from the four-trial programme built to confirm it.

What circulates instead — 28% at 80 weeks, 30.3% at 104 weeks, phase 3 attributions on a phase 2 number — is either press reporting of a company statement or, as on our own page until today, simply wrong.

Meanwhile this platform holds 1,150 independent lab tests of a drug that no regulator has approved anywhere in the world. The supply chain is better documented than the medicine, and that is the single most useful thing we can tell you about retatrutide.

Browse the weight loss and metabolic peptides category, or our complete peptide guide with 118 compounds (verified August 2026). For per-injection volume, use the retatrutide calculator alongside the reconstitution calculator. Compare shops through independent lab tests and community-verified shop reviews.

This article is for educational and informational purposes only and does not constitute medical advice. Peptides discussed may be investigational compounds not approved by the FDA (or equivalent regulators in your jurisdiction) for human use. Always consult a qualified healthcare provider before using any peptide or research compound. Peptigrity is an independent review platform and does not sell, endorse, or recommend specific products or vendors.