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 (Aug 2026)
- Phase 3 is no longer 'ongoing' — several registrational trials completed in April-May 2026 and the first phase 3 result was published in June 2026. Still not approved anywhere.
- Reported trial range
- Phase 2 escalated to 12 mg once weekly; the published phase 3 used fixed 4 mg, 9 mg and 12 mg arms (reported, not an established dose).
- Route reported
- Subcutaneous injection.
- Reported frequency
- Once weekly.
- 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.
Reported ranges from research/community — examples, not recommendations.
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
Three trial tiers now exist, 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. Note the gap between the tiers — the 15.3% weight reduction at 12 mg in a 40-week diabetes trial is a materially smaller number than the 24% reported at 12 mg over 48 weeks in the phase 2 obesity population, and comparing them directly would be comparing different populations, durations and endpoints. Anyone quoting '24%' as retatrutide's weight-loss figure is quoting the phase 2 obesity trial, not the phase 3 diabetes result.
Evidence & regulatory status
- Evidence: now substantial for efficacy in company-run trials — one phase 2 obesity trial, one phase 2a liver study, and a published phase 3 in type 2 diabetes (TRANSCEND-T2D-1, Lancet 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 no longer recruiting-and-ongoing in the way most pages still describe it. TRIUMPH-1 (NCT05929066, n=2,335) completed on 30 April 2026 and the cardiovascular-disease trial NCT05882045 (n=1,946) completed on 14 May 2026. Their results were not yet published in the peer-reviewed literature at the time this page was last verified.
- 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.
Dosage — reported ranges (overview)
There is no established or approved regimen, and the figures below describe what trials administered rather than what anyone should take. The phase 2 obesity trial began at 2 mg weekly and escalated stepwise through 4 mg and 8 mg to 12 mg, with the escalation designed specifically to limit gastrointestinal effects. The published phase 3 in type 2 diabetes randomised participants to fixed maintenance doses of 4 mg, 9 mg or 12 mg once weekly — note the 9 mg arm, which does not appear in the phase 2 ladder and is not part of any community protocol. Discontinuations for adverse events in that trial ran 2-5% on retatrutide against 0% on placebo, and no severe hypoglycaemia was reported. Community 'ladders' are extrapolations from published trial designs; no dose has been shown safe or effective outside a clinical trial.
A printable protocol sheet with a reconstitution reference and an injection log comes with All-Access Lifetime.
Reconstitution — bac-water math
Retatrutide ships as a research-grade lyophilised powder and is reconstituted with bacteriostatic water before anything can be measured. Because trial doses are in whole milligrams rather than micrograms, the useful figure is concentration in mg per mL: concentration = vial mg divided by mL of water added. On a U-100 insulin syringe 100 units = 1 mL, so units = (dose in mg divided by concentration) x 100. The table below works a 10 mg vial — the size the reconstitution question is most often asked about — at three water volumes, with columns for 2 mg and 4 mg examples from the published trial range. One practical constraint is worth stating rather than hiding: at 3 mL of water a 10 mg vial gives 3.33 mg/mL, and a 4 mg example would require 1.2 mL, or 120 units, which does not fit a 1 mL U-100 syringe at all. That is why the table stops at 2 mL. Check this arithmetic yourself against your own vial rather than assuming a chart written for a different vial size applies.
| Bac water added | Concentration | 2 mg (trial-range example) | 4 mg (trial-range example) |
|---|
| 1 mL | 10 mg/mL | 20 units | 40 units |
| 1.5 mL | 6.67 mg/mL | 30 units | 60 units |
| 2 mL | 5 mg/mL | 40 units | 80 units |
This is concentration math, not a dose recommendation.
Injection / administration basics
In every trial retatrutide was given subcutaneously once weekly with standard sterile technique and site rotation. Any use outside a clinical trial is unapproved investigational use of a molecule with no label anywhere in the world. General handling concepts — sterile technique, site rotation, consistent weekly timing — are covered here as general information. This is educational information about how the trials were run, not a personal administration protocol.
Half-life & frequency rationale
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.
Side effects, safety & contraindications
Across phase 2 and phase 3 the dominant adverse events were gastrointestinal — nausea, vomiting, diarrhoea and constipation — described in the 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. 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, not a safety clearance.
Stacking — overview
Retatrutide already engages the two receptors that other incretin drugs target plus a third. Adding a separate GLP-1 or GIP agonist is redundant at the receptor level and compounds the gastrointestinal and cardiovascular effects that are already the dose-limiting problem, which is why it is consistently described as a run-solo compound rather than a stack component. The one genuinely mechanical consideration is switching: because retatrutide is dosed weekly and titrated over weeks, sources describe a washout matched to the prior drug's own dosing interval rather than an immediate substitution.
Run solo
Retatrutide is already a triple agonist — a companion GLP-1/GIP agonist adds risk, not mechanism.
Avoid GLP-1/GIP combinations
Combining with semaglutide, tirzepatide or similar is receptor-redundant and raises GI, hypoglycaemia and cardiovascular risk.
Switching agents
Moving from another weekly incretin, sources describe a washout of roughly four to five weeks matched to the prior drug's half-life rather than an overlapping change.
Stacking across compounds
The overview above covers Retatrutide. The cross-compound material — which pairings are redundant rather than additive, where interaction risk is documented versus merely unstudied, and the blend arithmetic worked end to end — lives in the Peptide Stacking Guide, which is free to read in outline and $39 in full (included with All-Access Lifetime).
Included with this guide
The Retatrutide Stacking Module
The overview above is the free summary. The Retatrutide Stacking Module goes through each combination in depth — the mechanism-level reason it is proposed, what is actually reported in practice, and the cautions specific to that pairing — plus what to avoid and why. Included with Retatrutide Standard Access.
- How to think about stacking Retatrutide — 4 principles
- 2 combinations covered in detail
- What to avoid, and why — 3 items
- Combination-specific cautions
Combinations covered: Amylin pairing (reported), Lean-mass preservation discussion.
For how combinations are grouped by research context, the named blends, and why a pre-mixed blend vial cannot be calculated from its total milligrams, see the peptide stacks guide.
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 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, NCT05882045, NCT06662383 and the expanded access record NCT07629401; and the FDA drug-label database, which returns no retatrutide label. Trial status verified 12 August 2026 — retatrutide is an actively developing programme and this section should be re-checked rather than assumed current.
Evidence File
The Retatrutide Evidence File: Registry Records, Posted Results and the Name-Search Gap
Retatrutide has one of the largest development programmes in metabolic medicine and one of the thinnest public result sets relative to its size. This module rebuilds that record from primary sources fetched directly: every ClinicalTrials.gov record returned under both of the molecule's names, the posted registry results tables with their standard errors and participant flow, PubMed E-utilities searches with each returned identifier resolved, and the FDA databases. It reports the per-arm numbers, the completion figures, the serious-event terms, and the exact searches that established each absence. Where it corrects the free page, it says so.
- 35 registry records, complete only when both names are searched
- 2 trials with posted results; the four completed TRIUMPH trials have none
- 5,878 participants in four completed trials with nothing published
- 0 terminated, withdrawn or suspended trials across the programme
Two names, and two literatures that do not overlap
The six-day half-life is cited, and the citation is filed under the old name
The seven-arm table underneath the headline
Who finished, and who did not respond
The serious-event table, term by term
The primary endpoint was 17.5 percent, and the comparator arm nobody quotes
Fourteen phase 3 records, and a phase 2 record that is not Lilly's
Completed, unpublished, and the questions that sit behind those records
8 more sections in the Evidence File for Retatrutide
Unlock the Evidence File, Sourcing File and Benefit & Outcome Review for Retatrutide for $14 — or every compound in the library, plus the printable protocol sheets, for $99.
The twelve sections above this one, and every calculator on the site, stay free to read without an account.
Sourcing File
The Retatrutide Sourcing File: Twelve Labels, One Recall and a Mass That Cannot See Stereochemistry
A retatrutide certificate of analysis is unusually easy to read wrongly, because the public chemistry databases for this molecule contain several traps that a vendor can fall into honestly. This module resolves the identifiers from the FDA substance registry, PubChem, DailyMed and the FDA product directories, recomputes the masses from the molecular formula rather than copying them, works the counterion and fill arithmetic through to what a syringe actually delivers, and reads a research-grade certificate line by line. One statement the free guide makes is corrected here, and the correction is the most useful sourcing artefact this compound has.
- 12 FDA-listed retatrutide labels, none of them from Eli Lilly
- 4728.4718 Da monoisotopic, recomputed independently from the formula
- 4 isobaric PubChem records under one name, 3 distinct stereo layers
- 1 Class II recall, inside 57 recalls at a single compounding firm
The identifiers, and the mass field that gets copied wrong
The PubChem trap: five compound records, and one of them is a different molecule
Counterion, purity and fill: three modest deductions that multiply
The FDA label database now returns retatrutide, and that is the problem
The recall is real, and it is not about retatrutide
What a certificate must show, and the three numbers that decide the arithmetic
6 more sections in the Sourcing File for Retatrutide
Unlock the Evidence File, Sourcing File and Benefit & Outcome Review for Retatrutide for $14 — or every compound in the library, plus the printable protocol sheets, for $99.
The twelve sections above this one, and every calculator on the site, stay free to read without an account.
Benefit & Outcome Review
Retatrutide Claim by Claim: What Was Measured, in Whom, and How Far Each Result Carries
Retatrutide arrives with more circulating claims than most compounds have publications. This module takes each one in turn and asks four questions of it: what was actually measured, in which species and which population, against which comparator, and for how long. Human results, animal results and cell experiments are kept strictly apart, because several of the most confident claims about this molecule change category when that separation is enforced. Effect sizes come from published abstracts, one open-access full text and posted registry results tables fetched directly. Where a claim has no measurement behind it, or has one that was never reported, that is recorded as the finding.
- 4 endpoints where 8 mg matches or beats 12 mg
- 17% of top-dose participants did not reach 15% weight loss
- 0 published head-to-head trials against tirzepatide or semaglutide
- 1 completed human energy-expenditure trial, still unreported
The 24 percent claim, and what it is 24 percent of
Blood sugar, in a population selected to flatter the result
Liver fat: strong on imaging, silent on histology
Lean mass and fat mass: only one of the two has numbers
Appetite and energy expenditure: what species each mechanism claim comes from
Tolerability and heart rate: what rises, and with what
Four endpoints where 8 mg matches or beats 12 mg
Claims with nothing measured behind them, and one measured and unreported
8 more sections in the Benefit & Outcome Review for Retatrutide
Unlock the Evidence File, Sourcing File and Benefit & Outcome Review for Retatrutide for $14 — or every compound in the library, plus the printable protocol sheets, for $99.
The twelve sections above this one, and every calculator on the site, stay free to read without an account.
Related peptide guides
Continue exploring related educational guide topics in the Medibact library.
Guide FAQ
Quick answers about guide scope, access, and educational use context.
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. The TRIUMPH programme spans four phase 3 studies in more than 5,800 participants; TRIUMPH-1 (NCT05929066, 2,335 participants) completed on 30 April 2026 and the cardiovascular-disease trial NCT05882045 (1,946 participants) completed on 14 May 2026, while other phase 3 trials remain active. The first phase 3 result to reach the peer-reviewed literature was TRANSCEND-T2D-1 in the Lancet on 13 June 2026. Pages describing phase 3 as simply 'ongoing with no results' are describing the position before June 2026.
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.
How much weight loss did retatrutide show in research?
It depends which trial. The widely quoted figure of roughly 24% comes from the phase 2 obesity trial at 12 mg over 48 weeks (NEJM 2023). The published phase 3 in type 2 diabetes reported 15.3% at the same 12 mg dose over 40 weeks — a different population, a different duration and a different primary endpoint. Neither is a guaranteed outcome, and quoting the phase 2 number as though it were the drug's general result overstates it.
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 used fixed 4 mg, 9 mg and 12 mg maintenance arms. Community ladders are extrapolations from those published designs, not validated protocols.
How do you reconstitute a 10 mg retatrutide vial?
Concentration equals vial milligrams divided by millilitres of bacteriostatic water added, and units on a U-100 syringe equal dose divided by concentration times 100. A 10 mg vial with 1 mL of water gives 10 mg/mL, so a 2 mg example is 20 units and a 4 mg example is 40 units; with 2 mL it gives 5 mg/mL, so the same examples are 40 and 80 units. At 3 mL the concentration drops to 3.33 mg/mL and a 4 mg example would need 120 units, which will not fit a 1 mL U-100 syringe — a practical reason larger water volumes stop being useful on a 10 mg vial.
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.
Can retatrutide be stacked with semaglutide or tirzepatide?
It is consistently described as run-solo. It already activates GLP-1 and GIP alongside glucagon, so a second incretin agonist adds no mechanism while compounding the gastrointestinal and cardiovascular effects that already limit the dose.
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.
