Retatrutide

Last Updated: August 2026

Retatrutide, also designated LY3437943, is a 39-amino-acid investigational triple-receptor agonist activating GLP-1, GIP, and glucagon receptors. Developed by Eli Lilly and currently in the Phase 3 TRIUMPH program, retatrutide is not approved by the FDA or any other regulator for any indication and is supplied strictly for research use only. The lab test table and shop directory above show Peptigrity's independent verification data for retatrutide, updated continuously as new HPLC tests are submitted.

What is retatrutide and why does the triple-agonist mechanism matter?

Retatrutide is the first triple GLP-1 / GIP / glucagon receptor agonist to reach Phase 3 clinical trials, distinguishing it from semaglutide (single GLP-1 agonist) and tirzepatide (dual GLP-1/GIP). The glucagon component is the new variable — in human trials, it appears to drive direct energy expenditure and hepatic fat clearance, mechanisms unavailable to single or dual agonists. The full receptor pharmacology, signaling pathways, and TRIUMPH-program design are covered in our retatrutide triple-agonist science guide.

What does the Phase 3 evidence show?

Retatrutide's strongest published evidence remains a Phase 2 obesity trial: at the 12 mg dose, participants lost an average of 24.2% of body weight at 48 weeks (n=338).1 source In 2026 the first Phase 3 results were published — TRANSCEND-T2D-1, in adults with type 2 diabetes — where 12 mg retatrutide lowered HbA1c by roughly 1.9 percentage points and reduced body weight by about 15% over 40 weeks.1 source Larger obesity figures exist only as company-reported topline, not yet peer-reviewed: TRIUMPH-1 (obesity) described about 28% average weight loss at the 12 mg dose over 80 weeks, presented at a scientific meeting in 2026, and TRIUMPH-4 (obesity with knee osteoarthritis) about 28.7% at 68 weeks alongside reduced knee pain, reported by press release in December 2025. No TRIUMPH results have been published in a peer-reviewed journal as of August 2026; read those numbers as press readouts pending full publication. Further TRIUMPH readouts across obesity, obstructive sleep apnea and knee osteoarthritis are expected. Evidence level: Human RCT — published Phase 2 (obesity) and Phase 3 (type 2 diabetes, TRANSCEND-T2D-1); obesity Phase 3 (TRIUMPH) is company topline, peer-reviewed publication pending.

How does retatrutide compare to semaglutide and tirzepatide?

Retatrutide produces larger percent weight loss than either semaglutide or tirzepatide at matched trial durations, though no head-to-head Phase 3 data exists yet — TRIUMPH-5 is the active-comparator trial currently in progress. Tirzepatide reported approximately 22.5%1 source weight loss in SURMOUNT-1 at 72 weeks; semaglutide reported 14.9%1 source in STEP 1 at 68 weeks. Retatrutide's directly comparable published figure is its Phase 2 obesity result — 24.2% at 48 weeks1 source; its larger Phase 3 obesity numbers (~28% in TRIUMPH-1, 28.7% in TRIUMPH-4) are company topline, not yet peer-reviewed, so head-to-head ranking against the published semaglutide and tirzepatide trials should wait for the full TRIUMPH publications.

What are the documented side effects of retatrutide?

In the published Phase 2 obesity trial, the most common retatrutide side effects were dose-dependent gastrointestinal events — nausea, diarrhoea, vomiting and constipation — most frequent at the 12 mg dose and the main driver of discontinuations.1 source Retatrutide also carries a distinctive, dose-dependent cutaneous dysesthesia — an unusual skin sensation — reported at roughly one in five participants on the 12 mg dose in company Phase 3 topline (TRIUMPH-4); it is a signal not prominent with GLP-1 or GLP-1/GIP agonists and is attributed to glucagon-receptor activity. The signal appears in the obesity and knee-osteoarthritis programs; the published type 2 diabetes trial (TRANSCEND-T2D-1) instead reported gastrointestinal events as the most frequent, mild-to-moderate and easing over time.1 source among the GLP-1 class and has been characterized across three Phase 3 populations (TRIUMPH-1, TRIUMPH-4, TRANSCEND-T2D-1). The full dose-by-dose adverse event breakdown, including the 104-week extension data, is in our retatrutide side effects guide. Evidence level: Human RCT (Phase 3).

What is the regulatory status of retatrutide?

Retatrutide is not approved for any indication, anywhere in the world, as of August 2026. Unlike semaglutide and tirzepatide, it was never on the FDA drug-shortage list and never had a legal compounding pathway — there is no pharmacy-compounded reference product, only research-grade material. Eli Lilly is pursuing FDA and EMA approval through the TRIUMPH program; NDA filing is contingent on the full Phase 3 readout package, with industry analysts estimating regulatory approval most plausibly in 2027–2028. Retatrutide is sold strictly as a research-use-only compound by third-party laboratories, with no approved prescription pathway. Country-specific import rules apply — see our peptide regulatory status by country guide.

Why does retatrutide vendor verification matter more than for older GLP-1s?

Retatrutide's narrower manufacturing base, higher market price, and absence of an FDA-approved reference product create wider purity variance and stronger economic incentive for underdosing than older GLP-1 compounds. The triple-agonist synthesis adds complexity that fewer laboratories have optimized at scale. Independent HPLC purity testing and mass spectrometry identity confirmation (expected molecular weight 4,731.4 Da1 source) are the only meaningful purity signals a research-grade vendor can provide. Learn how to interpret these in our how-to-test-peptides hub and the reading peptide lab test results guide.

How does Peptigrity verify retatrutide vendors?

Peptigrity collects independent third-party Certificates of Analysis for retatrutide from shops' official channels and verifies each for authenticity before publishing. Because shops choose which COAs to publish, results reflect the batches shops have made public rather than every production batch — a selection bias we state openly. A community-funded Testing Grant to purchase and test vials anonymously is in development. The lab test table above this section shows the full cross-shop dataset, sortable by date, purity, and labeled-vs-tested quantity. Tests are sourced from named labs including Janoshik Analytical, Freedom Diagnostics, Chromate, Trust Pointe Analytics, and Krause Analytical. Our verification methodology — including the trust score weighting of reviews (50%) and lab purity (50%) — is documented in how we calculate trust scores.

Frequently Asked Questions

How can I verify a retatrutide vendor is selling real product?

The only reliable purity signal is an independent third-party HPLC certificate of analysis from a lab the vendor does not own or pay — not a vendor-published COA on vendor letterhead. Peptigrity publishes independent retatrutide test results from independent labs in the table above. For COA interpretation, see red flags in peptide certificates of analysis.

Is retatrutide legal to purchase?

Retatrutide is legal to purchase as a research chemical for laboratory use in most jurisdictions including the United States and most EU member states, but it is not approved for human consumption. Buyers are responsible for verifying local import rules — full country-by-country breakdown in our peptide legal status guide.

When will retatrutide be FDA-approved?

No FDA approval has been granted as of August 2026. Eli Lilly has reported topline results from two Phase 3 trials (TRIUMPH-4 in December 2025; TRIUMPH-1 in May 2026), with five more readouts expected through late 2026. Industry analysts estimate NDA filing in late 2026 with FDA approval most plausibly in 2027–2028. Track regulatory developments in FDA peptide regulation 2025–2026: the complete timeline.

Why is retatrutide more expensive than semaglutide or tirzepatide?

Three factors: synthesis complexity (triple-agonist modification requires additional steps), narrower manufacturing base (fewer labs have optimized production at scale), and demand outpacing supply since the Phase 2 publication. Expect prices to fall as additional manufacturers come online post-TRIUMPH approval. Current research-grade market range is broken down in how much do peptides cost.

Does Peptigrity recommend a retatrutide dose?

No. Retatrutide is not approved for human consumption and Peptigrity is an independent review platform, not a medical authority. The doses tested in Phase 3 (4 mg, 9 mg, 12 mg weekly) were administered under clinical supervision with full monitoring — translating these into a self-administration protocol is medical practice. Anyone considering use of investigational compounds should consult a licensed physician.

How does retatrutide compare to other triple agonists in development?

Retatrutide is currently the only Phase 3 triple agonist with reported weight-loss data. Other multi-receptor agonists in earlier-stage development include survodutide (GLP-1/glucagon dual) and mazdutide (GLP-1/glucagon dual). A full dual-vs-triple agonist comparison is planned for publication when TRIUMPH-2 and TRIUMPH-3 read out.

This section is for educational and informational purposes only and does not constitute medical advice. Retatrutide is an investigational compound not approved by the FDA or any other regulator 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.