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Retatrutide Guide: Evidence & Sourcing

What retatrutide is, where its phase 3 programme actually stands as of October 2026, the reported trial doses, and an honest account of what a research-grade vial's documentation can and cannot tell you. Educational use only, not medical advice.

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Retatrutide educational module visual
Foundational Guide: Available Now

Educational use only — not medical advice. This guide summarizes information reported in published research and community practice for educational purposes. It is not medical advice and not a recommendation to use any compound. Any doses, schedules, or combinations shown are examples of what has been reported, not instructions for you. Many peptides described here are research compounds that are not FDA-approved for the uses discussed and may be investigational or restricted. Effects, risks, and legal status vary; individual needs and results vary. Consult a qualified, licensed healthcare professional before making any decision. Do not use this content to diagnose, treat, or dose yourself.

Retatrutide at a glance

What it is
Retatrutide (LY3437943) — a single investigational peptide that activates three receptors at once: GIP, GLP-1 and glucagon.
Researched for
Obesity, type 2 diabetes, MASLD, obstructive sleep apnea and knee osteoarthritis — in company-run trials only.
Trial status (Oct 2026)
Three phase 3 results are published: TRANSCEND-T2D-1 in type 2 diabetes (June 2026), and TRIUMPH-1 in obesity and TRIUMPH-2 in obesity with type 2 diabetes (both 29 September 2026). Still not approved anywhere.
Reported trial range
Phase 2 escalated to 12 mg once weekly; the published phase 3 trials used fixed 4 mg, 9 mg and 12 mg arms (reported, not an established dose).
Plasma half-life
No numeric half-life appears in the published phase 1 abstract; it reports a PK profile 'supporting once-weekly dosing' and a weight effect persisting to day 43 after one dose.
Regulatory status
Not approved anywhere. No FDA label, no USP monograph, no official reference standard. Non-trial material is research-use-only.

Educational reference. This page does not publish dose ranges or reconstitution arithmetic.

What it is / mechanism

Retatrutide is a single synthetic peptide engineered to agonise three receptors simultaneously: the glucose-dependent insulinotropic polypeptide (GIP) receptor, the glucagon-like peptide-1 (GLP-1) receptor and the glucagon receptor. The GLP-1 and GIP arms are shared with tirzepatide; the glucagon arm is what makes it a triple agonist rather than a dual one, and is hypothesised to raise energy expenditure and mobilise hepatic fat rather than only suppress appetite. Fatty-acid acylation extends its circulation time enough to support weekly administration. The phase 1 single-ascending-dose study (Coskun et al., Cell Metab 2022) describes the molecule from discovery through first-in-human proof of concept and reports that its pharmacokinetic profile supported once-weekly dosing, with a reduction in body weight still present at day 43 after a single dose. That day-43 observation is the most concrete published durability figure in the early record, and it is worth more than the half-life numbers that circulate without a citation attached.

Researched effects

The trial record now has three layers, and they say different things. Phase 2 in obesity (Jastreboff et al., NEJM 2023; 48 weeks) produced a least-squares-mean body-weight reduction of roughly 24% at 12 mg versus about 2% for placebo — the figure that made retatrutide famous. A phase 2a study in metabolic dysfunction-associated steatotic liver disease (Nature Medicine 2024) reported reductions in liver fat. The first published phase 3, TRANSCEND-T2D-1 (Lancet, 13 June 2026; NCT06354660), is a 40-week monotherapy trial in 537 adults with type 2 diabetes inadequately controlled by diet and exercise: HbA1c fell 1.69% (4 mg), 1.86% (9 mg) and 1.94% (12 mg) against 0.81% on placebo, and body weight fell 11.5%, 13.9% and 15.3% against 2.6% on placebo. The two phase 3 weight trials followed on 29 September 2026. TRIUMPH-1 (NEJM; NCT05929066) randomised 2,339 adults with obesity and no diabetes for 80 weeks: mean body weight changed by -17.6% (4 mg), -23.7% (9 mg) and -25.0% (12 mg) against -3.9% on placebo, and the trial also reported less knee pain in its 574 participants with knee osteoarthritis and fewer breathing interruptions during sleep in its 243 with obstructive sleep apnea. TRIUMPH-2 (Lancet; NCT05929079) randomised 1,152 adults with obesity and type 2 diabetes for 80 weeks: -11.9%, -16.8% and -18.8% against -5.1% on placebo. Read the layers apart: in these trials the figures for people with type 2 diabetes (15.3% at 40 weeks, 18.8% at 80 weeks, both at 12 mg) sit below those for people without diabetes (about 24% at 48 weeks in phase 2, 25.0% at 80 weeks in phase 3), so a number from one population does not describe the other. The phase 2 '24%' figure has now been matched in phase 3, over a longer trial and in about seven times as many people. Higher numbers circulate from Eli Lilly's topline announcements made before the papers (for TRIUMPH-1, 28.3% at 80 weeks); this page reports the figures the peer-reviewed papers give in their abstracts.

Evidence & regulatory status

  • Evidence: now substantial for efficacy in company-run trials — one phase 2 obesity trial, one phase 2a liver study, and three published phase 3 trials: TRANSCEND-T2D-1 (Lancet, June 2026), TRIUMPH-1 (NEJM, 29 September 2026) and TRIUMPH-2 (Lancet, 29 September 2026). Every trial to date is funded by Eli Lilly, which is normal for a molecule at this stage but is a fact a reader should have.
  • Trial status: the phase 3 TRIUMPH programme (over 5,800 participants across four trials, per the design paper in Diabetes, Obesity and Metabolism, January 2026) is reporting. TRIUMPH-1 (NCT05929066) completed on 30 April 2026 and was published in NEJM on 29 September 2026; the paper reports 2,339 randomised, the registry 2,335 enrolled. TRIUMPH-2 (NCT05929079, 1,152) completed on 16 June 2026 and was published in the Lancet the same day as TRIUMPH-1. TRIUMPH-3, the trial in people with cardiovascular disease (NCT05882045, 1,946), completed on 14 May 2026; Eli Lilly announced topline results in July 2026, but no journal publication was found in PubMed on 3 October 2026, and none of the three registry records shows posted results. TRIUMPH-5, the head-to-head trial against tirzepatide (NCT06662383), is active, not recruiting, with primary completion listed for November 2026.
  • Regulatory: not approved in any jurisdiction. A search of the FDA drug-label database returns no retatrutide label. Eli Lilly does operate a pre-approval single-patient expanded access protocol (NCT07629401, status 'available') for adults with severe obesity and at least two serious obesity-related complications who are refractory to available treatment — that is a named-patient pathway through a physician, not a route by which research-grade material becomes legitimate.
  • Research use: non-trial material is research-use-only and is not an approved medicine.

Research timeline

Dated milestones taken from the primary records: the molecule's discovery, its first registered human study, the trials that shaped the evidence and the regulatory decisions. Each entry links to the record it comes from.

  1. Eli Lilly scientists publish the discovery of LY3437943, a single peptide that activates the glucagon, GIP and GLP-1 receptors. In a first single-dose study in humans its profile supported once-weekly use, and weight stayed lower up to day 43. PMID 35985340
  2. A 12-week phase 1b trial in 72 adults with type 2 diabetes, run from December 2019 to December 2020, reports a half-life of about six days, gastrointestinal complaints as the most frequent adverse events, and lower glucose and body weight in the three highest dose groups. PMID 36354040
  3. The phase 2 obesity trial (338 adults, 48 weeks) is published in the New England Journal of Medicine: mean body weight fell 24.2% at the highest dose against 2.1% with placebo. PMID 37366315
  4. The phase 2 type 2 diabetes trial (281 adults, 42 US centres) is published in The Lancet: HbA1c fell by up to 2.02 percentage points at 24 weeks against 0.01 with placebo, and body weight by up to 16.9% at 36 weeks. PMID 37385280
  5. A liver-fat substudy of the obesity trial (98 participants with fatty liver disease) reports liver fat down 82.4% at 24 weeks at the highest dose, against a 0.3% rise with placebo. PMID 38858523
  6. TRANSCEND-T2D-1, the first published phase 3 trial (537 adults with type 2 diabetes, 40 weeks), reports HbA1c down 1.94 percentage points at the highest dose against 0.81 with placebo, with no severe hypoglycaemia. PMID 42250575
  7. TRIUMPH-1 (2,339 adults with obesity, no diabetes, 80 weeks) is published in the New England Journal of Medicine: body weight fell 25.0% at the highest dose against 3.9% with placebo, and knee-osteoarthritis pain scores improved more than with placebo. PMID 42814954
  8. TRIUMPH-2 (1,152 adults with obesity and type 2 diabetes, 80 weeks) is published in The Lancet: body weight fell 18.8% at the highest dose against 5.1% with placebo; gastrointestinal events were the most common, and low blood pressure and abnormal skin sensations (dysaesthesia) were more frequent than with placebo. PMID 42810372

Records checked Oct 3, 2026

Claims at a glance

The claims most often made about this compound, each with the strongest kind of evidence we found for it. The grade says what was studied, not whether the claim is true; the line beside it says what that study showed.

  • Produces about 25% weight lossHuman, randomised trial. TRIUMPH-1, 2,339 adults with obesity and no diabetes: −25.0% at 80 weeks on the highest dose against −3.9% on placebo; the phase 2 trial had shown −24.2% at 48 weeks. PMID 42814954
  • Lowers blood sugar in type 2 diabetesHuman, randomised trial. TRANSCEND-T2D-1, 537 adults with early type 2 diabetes (2.5 years on average): HbA1c fell by up to 1.94 points against 0.81 on placebo at 40 weeks. PMID 42250575
  • Clears fat from the liverHuman, randomised trial. A 98-person substudy: liver fat fell by about 82% on the highest dose against no change on placebo at 24 weeks, measured by MRI, not biopsy. PMID 38858523
  • Burns fat but spares muscleHuman, randomised trial. A body-scan substudy in type 2 diabetes measured large falls in fat mass at 36 weeks; the published abstract gives no figures for lean mass. PMID 40609566
  • Works better than tirzepatide or semaglutideNo study found. No head-to-head result has been published; the trial against tirzepatide is still running, with primary completion expected in November 2026. NCT06662383

The reasoning behind each grade, study by study, is in this guide's Benefit & Outcome Review.

Grades checked Oct 5, 2026

A printable reference sheet with the compound's key facts, storage guidance and a vial record comes with All-Access Lifetime.

Half-life & pharmacokinetics

This is a case where the honest answer is narrower than the one in circulation. A figure of roughly six days is widely repeated on commercial pages, usually without a citation. What the published phase 1 abstract (Cell Metab 2022) actually states is that retatrutide's pharmacokinetic profile 'supported once-weekly dosing' and that a reduction in body weight persisted to day 43 after a single dose — it reports the dosing conclusion and a durability observation rather than a headline half-life number in the abstract itself. A weekly dosing interval is consistent with a multi-day half-life, and stepwise titration over several weeks is consistent with a drug that takes roughly a month to reach steady state at each level. If you encounter a specific half-life figure for retatrutide, the useful question is which study produced it and in which population, because the answer is not in the abstracts of the trials most often cited for it.

Reported side effects & toxicology

Across phase 2 and phase 3 the dominant adverse events were gastrointestinal — nausea, vomiting, diarrhoea and constipation — described in the first phase 3 trial as generally mild to moderate and subsiding over time. Their dose-relatedness is the entire reason both trials titrated. The phase 3 monotherapy trial reported no severe hypoglycaemia and 2-5% discontinuation for adverse events versus 0% on placebo; two deaths occurred, both in the 4 mg group and both assessed as unrelated to study drug. TRIUMPH-2, 80 weeks in people with obesity and type 2 diabetes, recorded more on retatrutide: diarrhoea in 27-34% of participants against 13% on placebo, nausea in 14-28% against 8%, low blood pressure in 1-6% against under 1%, and dysesthesia (abnormal skin sensations) in 4-7% against 1%. Permanent discontinuation for adverse events or death was 4%, 12% and 8% in the 4 mg, 9 mg and 12 mg groups against 5% on placebo; six participants died on retatrutide and one on placebo, all judged unrelated to the study drug by the investigators. TRIUMPH-1 reports gastrointestinal events as the most common. Increases in heart rate and transient glucose effects attributed to glucagon-receptor activation have been noted as areas under study. Because there is no approved label there is no boxed warning, no established contraindication list and no approved patient-selection criteria; class considerations for GLP-1/GIP agonists, such as caution with a personal or family history of medullary thyroid carcinoma or MEN 2, are anticipated for retatrutide but not established for it. This is a summary of published trial safety reporting.

Storage & handling

  • Lyophilised (unmixed): store cool and dark per the supplier's stated conditions; long-term storage is typically frozen.
  • Reconstituted: refrigerate at roughly 2-8°C, protect from light and do not freeze once mixed. The commonly cited bacteriostatic-water window of about 28-56 days is a community convention rather than a stability figure established for this molecule — no approved stability data exists for retatrutide in any reconstituted form, because there is no approved product.

References

Built from primary sources: the phase 3 TRANSCEND-T2D-1 trial (Lancet, 13 June 2026, PMID 42250575, NCT06354660); the phase 3 TRIUMPH-1 trial (Jastreboff et al., NEJM, 29 September 2026, PMID 42814954, NCT05929066); the phase 3 TRIUMPH-2 trial (Bellido et al., Lancet, 29 September 2026, PMID 42810372, NCT05929079); the phase 2 obesity trial (Jastreboff et al., NEJM 2023, PMID 37366315); the phase 2a MASLD study (Nature Medicine 2024, PMID 38858523); the TRIUMPH registrational design paper (Diabetes, Obesity and Metabolism, January 2026, PMID 41090431); the phase 1 discovery-to-proof-of-concept report (Cell Metab 2022, PMID 35985340); ClinicalTrials.gov records NCT05929066, NCT05929079, NCT05882045, NCT06662383 and the expanded access record NCT07629401; the FDA drug-label database, which returns no retatrutide label; and, for the GLP-3 nickname, Public Citizen, "The Miracle Drug and the Peptide Craze" (16 June 2026). Trial status verified 3 October 2026 — retatrutide is an actively developing programme and this section should be re-checked rather than assumed current.

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Guide FAQ

Quick answers about guide scope, access, and educational use context.

Is GLP-3 another name for retatrutide?

Only as online slang. There is no human hormone, drug or drug class called GLP-3: in people the proglucagon gene gives rise to GLP-1 and GLP-2, and the numbering stops there. Retatrutide (LY3437943) is a single molecule that activates three receptors at once — GIP, GLP-1 and glucagon — and the nickname appears to play on that triple action. A Public Citizen report published on 16 June 2026 notes that users call retatrutide GLP-3, among other names, partly to get past social-media filters. Material sold under that label is not an approved medicine, and the label alone does not establish what a vial contains.

Is retatrutide FDA-approved?

No. Retatrutide (LY3437943) is not approved in any jurisdiction, and a search of the FDA drug-label database returns no retatrutide label. Eli Lilly operates a pre-approval single-patient expanded access protocol (NCT07629401) for adults with severe obesity and at least two serious obesity-related complications, which is a physician-mediated named-patient pathway rather than an approval. Non-trial material is research-use-only.

Is retatrutide still in phase 3, or has it finished?

Both, depending on the trial. Three phase 3 trials have now been published: TRANSCEND-T2D-1 (Lancet, 13 June 2026), and TRIUMPH-1 and TRIUMPH-2 (NEJM and Lancet, 29 September 2026). TRIUMPH-3, in people with cardiovascular disease, completed on 14 May 2026 without a journal publication found as of 3 October 2026, and other phase 3 trials, including the head-to-head against tirzepatide, remain active. Completed and published trials are still not an approval: no regulator has approved retatrutide.

What did the first published phase 3 trial of retatrutide show?

TRANSCEND-T2D-1 randomised 537 adults with type 2 diabetes inadequately controlled by diet and exercise to retatrutide 4 mg, 9 mg, 12 mg or placebo once weekly for 40 weeks. HbA1c fell 1.69%, 1.86% and 1.94% respectively against 0.81% on placebo, and body weight fell 11.5%, 13.9% and 15.3% against 2.6%. Adverse events were mostly mild-to-moderate gastrointestinal events that subsided over time, with no severe hypoglycaemia reported.

What did the TRIUMPH-1 phase 3 obesity trial show?

TRIUMPH-1 (NEJM, 29 September 2026; NCT05929066) randomised 2,339 adults with obesity and no diabetes to retatrutide 4 mg, 9 mg, 12 mg or placebo once weekly for 80 weeks. Mean body weight changed by -17.6%, -23.7% and -25.0% against -3.9% on placebo. In the 574 participants with knee osteoarthritis, knee pain scores fell more than on placebo, and in the 243 with obstructive sleep apnea, breathing interruptions fell by 22.9 to 34.3 events per hour against 9.9 on placebo. Gastrointestinal events were the most common adverse events. The trial was funded by Eli Lilly.

How much weight loss did retatrutide show in research?

It depends which trial. In people with obesity and no diabetes: roughly 24% at 12 mg over 48 weeks in phase 2 (NEJM 2023), and 25.0% at 12 mg over 80 weeks in the phase 3 TRIUMPH-1 trial (NEJM 2026), against 3.9% on placebo. In people with type 2 diabetes the figures are lower: 15.3% over 40 weeks in TRANSCEND-T2D-1 and 18.8% over 80 weeks in TRIUMPH-2, both at 12 mg. These are the peer-reviewed papers' headline figures; Eli Lilly's earlier topline announcements quoted higher ones (28.3% at 80 weeks for TRIUMPH-1). They are trial averages in supervised populations, not guaranteed outcomes, and the figures from one population do not carry over to another.

Is there a retatrutide reference standard?

No official one. A pharmacopeial reference standard is issued for molecules with an established monograph, and retatrutide — being unapproved anywhere — has no USP monograph and no official reference standard against which an identity or assay result could be certified. When a vendor's certificate of analysis cites a 'reference standard' for retatrutide it means an in-house or third-party comparator that the testing laboratory selected, not a pharmacopeial one. That is a meaningful distinction, and it is the reason two laboratories can report different purity figures for the same material without either being wrong.

What should retatrutide batch documentation actually contain?

For research-grade material, useful documentation names the analytical method (typically HPLC for purity and mass spectrometry for identity), the batch or lot reference, the date of analysis, the laboratory that performed it and the acceptance criteria applied. What it cannot contain is a pharmacopeial monograph reference, a sterility or endotoxin release specification tied to an approved product, or any statement of suitability for human use. Our guide to reading a peptide certificate of analysis walks through which fields on a report are checkable and which are decorative.

Is there an official retatrutide dose?

No. There is no approved dose because there is no approved product. Phase 2 escalated from 2 mg up to 12 mg weekly; the published phase 3 trials used fixed 4 mg, 9 mg and 12 mg maintenance arms. Community ladders are extrapolations from those published designs, not validated protocols.

How is retatrutide different from tirzepatide?

Tirzepatide is a dual GIP/GLP-1 agonist and is approved; retatrutide adds a third receptor, glucagon, and is not approved anywhere. In their separate trials retatrutide reported larger weight and liver-fat effects, but the two have not been compared head-to-head in a published trial — a phase 3 comparison against tirzepatide (NCT06662383) is registered and active, so that gap is a matter of timing rather than a permanent unknown.

Compliance and trust notes

  • Educational content only; no personalized health or outcome claims.
  • No personalized use recommendation outputs.
  • Use this material for general learning and research-context literacy.

Reading a Retatrutide certificate of analysis

A certificate of analysis (COA) is a laboratory’s report on one sample of one batch. The single most useful thing to know about it is that purity and identity are two separate results that fail in different ways. A high purity figure says the sample was mostly one substance; it does not say that substance was Retatrutide. Identity — normally a mass-spectrometry result matching the expected molecular weight — is what establishes what the material actually is, and a certificate reporting purity alone has not answered that question.

Two further limits are worth holding onto. Mass per vial is its own test: a vial can be 99% pure and still contain less material than the label claims. And sterility, endotoxin, heavy metals and residual solvent screening are separately commissioned tests, usually priced individually — so a “third-party tested” badge asserts none of them unless the certificate names them. Check that the batch or lot number on the document matches the vial in front of you; an unmatched certificate describes someone else’s material.

Specific to Retatrutide

Retatrutide is investigational and not approved anywhere, so there is no reference product to compare a certificate against — only the analysis of the batch in front of you. That makes the identity result (does the mass match the intended molecule) more informative than the purity percentage on its own.

Medibact does not test, endorse or resell peptides, and publishes no rating of any laboratory. How to read a peptide certificate of analysis walks through the document section by section, and what each COA field establishes covers the field-by-field detail and the laboratories that publish their methods.

You’ll need bacteriostatic water

The diluent for reconstituting Retatrutide

Reconstitution is volume arithmetic — it assumes a lyophilized vial is dissolved in bacteriostatic water, which is sterile water preserved with 0.9% benzyl alcohol. The preservative is what allows a vial to be entered more than once; plain sterile water carries none and is single-entry by design. Medibact supplies USP-grade Bacteriostatic Water for Injection in a 30 mL multi-dose vial, produced in an FDA-registered U.S. facility and shipped from the United States, for research use only. One 30 mL vial covers 30 reconstitutions at 1 mL each, 15 at 2 mL, or 10 at 3 mL — division only, not a dosing recommendation.

New to reconstitution? Read how to reconstitute peptides or bacteriostatic water vs sterile water. Medibact does not sell peptides.

Educational use only — not medical advice. This guide summarizes information reported in published research and community practice for educational purposes. It is not medical advice and not a recommendation to use any compound. Any doses, schedules, or combinations shown are examples of what has been reported, not instructions for you. Many peptides described here are research compounds that are not FDA-approved for the uses discussed and may be investigational or restricted. Effects, risks, and legal status vary; individual needs and results vary. Consult a qualified, licensed healthcare professional before making any decision. Do not use this content to diagnose, treat, or dose yourself.