Retatrutide (LY3437943)
1 product from 1 brand · free UK delivery · EU 3–7 days
Last reviewed · prices and listings checked by Free Muscle
Retatrutide, development code LY3437943, is an investigational peptide that acts as an agonist at three receptors at once: the glucose-dependent insulinotropic polypeptide (GIP) receptor, the glucagon-like peptide-1 (GLP-1) receptor and the glucagon receptor. Phase 3 trials have reported since late 2025, but no country has yet approved it as a medicine, and its developer has said it intends to seek US approval in early 2027. This page lists every brand of retatrutide stocked at Free Muscle and compares them on form, pack size and batch testing, alongside what the published trials actually report.
Research use only. Retatrutide on this page is supplied for laboratory research use only, to adults aged 18 or over. It is not for human consumption, and this page gives no dosing, usage or treatment information of any kind. What follows describes the compound, what the published studies report and how to compare the listing we stock.
What is retatrutide?
Retatrutide was engineered by Eli Lilly as a single peptide based on the GIP sequence; in its first human study, a single-dose trial, its pharmacokinetic profile supported once-weekly administration (Coskun 2022). Its distinguishing feature is glucagon receptor activity on top of the GIP and GLP-1 agonism found in existing licensed medicines.
Its status needs stating precisely. Retatrutide is an investigational medicine. Phase 2 trials in obesity and in type 2 diabetes were published in 2023, and the first Phase 3 papers followed in 2026, with further Phase 3 trials still running. It has no marketing authorisation from the MHRA, the EMA or the FDA, so it cannot be prescribed outside a clinical trial. It is not named individually on the WADA Prohibited List, but section S0 of the 2026 List bans at all times any substance not covered elsewhere on the List that has no current approval for human therapeutic use, including drugs in clinical development.
What the published research reports
The Phase 2 obesity trial randomised 338 adults with obesity or overweight to once-weekly subcutaneous retatrutide at several dose levels or placebo for 48 weeks. Body weight fell in a dose-related way, by up to about 24 per cent at 48 weeks in the highest-dose group compared with about 2 per cent on placebo. The most common adverse events were gastrointestinal (nausea, diarrhoea, vomiting, constipation), they were dose-related, and heart rate rose in a dose-dependent way, peaking at 24 weeks (Jastreboff 2023). The parallel Phase 2 trial in 281 people with type 2 diabetes reported reductions in HbA1c and body weight versus placebo and versus dulaglutide over 36 weeks, again with gastrointestinal adverse events in about a third of retatrutide participants (Rosenstock 2023).
In the Phase 3 trial TRIUMPH-1 (2,339 participants with obesity, none with diabetes, 80 weeks), mean weight fell by 17.6, 23.7 and 25.0 per cent in the three retatrutide arms versus 3.9 per cent with placebo, with gastrointestinal events again the most common (Jastreboff 2026).
TRIUMPH-2, in 1,152 people living with obesity and type 2 diabetes, found low blood pressure and dysaesthesia (abnormal skin sensation) more frequent than on placebo, and as many as 12 per cent in one retatrutide arm discontinued because of adverse events or death, compared with 5 per cent (Bellido 2026).
Two limitations dominate. Every trial used subcutaneous injection under clinical supervision with gradual dose escalation, and peptides of this size are largely broken down in the digestive tract, so nothing in the literature supports the idea that a capsule reproduces these results. And every trial was funded by the manufacturer, with the longest published follow-up at 80 weeks. None of the above is a claim about any product on this page.
- Jastreboff AM, et al. Triple-Hormone-Receptor Agonist Retatrutide for Obesity - A Phase 2 Trial. N Engl J Med. 2023;389(6):514-526. PMID: 37366315.
- Rosenstock J, et al. Retatrutide, a GIP, GLP-1 and glucagon receptor agonist, for people with type 2 diabetes: a randomised, double-blind, placebo and active-controlled, parallel-group, phase 2 trial conducted in the USA. Lancet. 2023;402(10401):529-544. PMID: 37385280.
- Coskun T, et al. LY3437943, a novel triple glucagon, GIP, and GLP-1 receptor agonist for glycemic control and weight loss: From discovery to clinical proof of concept. Cell Metab. 2022;34(9):1234-1247.e9. PMID: 35985340.
- Jastreboff AM, et al. Retatrutide, a Triple Hormone Receptor Agonist, for Treatment of Obesity. N Engl J Med. 2026. Online ahead of print. PMID: 42814954.
- Bellido V, et al. Retatrutide in adults with obesity and type 2 diabetes (TRIUMPH-2): a double-blind, parallel-group, randomised, placebo-controlled, phase 3 trial. Lancet. 2026. Online ahead of print. PMID: 42810372.
Brands of retatrutide we stock
- Free Muscle Retatrutide Research Peptide. Free Muscle brand, sold as capsules. The listing text does not yet state the strength per capsule or the number of capsules, so request the batch certificate before making any comparison. Every Free Muscle batch is assayed by Janoshik Analytical, an independent laboratory, and the certificate of analysis for the batch you hold is sent by email on request.
Retatrutide is currently stocked from Free Muscle only. If other brands are added they will be listed here with the same information so that the comparison stays consistent across the shop.
How to compare them
Where a strength per unit is stated, multiply it by the units in the pack to get total compound, and divide the price by that number for cost per milligram. With a peptide like this, check the form and route stated on the listing, because an injectable vial and a capsule are not interchangeable and the published trials used only one of them. Above all, ask for the batch certificate: for a compound this new, a certificate that confirms identity by mass spectrometry and states purity is the only evidence that the pack contains what the label says.
Batch testing and certificates of analysis
For a peptide this new, the batch certificate matters most. Identity should be confirmed by LC-MS (liquid chromatography with mass spectrometry), showing the mass expected for retatrutide rather than that of another peptide; purity, usually by HPLC, shows what share of the material is intact molecule rather than fragments; and any quantity reported per capsule can be checked against the label. Every Free Muscle batch is assayed by Janoshik Analytical, an independent laboratory, and its certificate reaches you by email once you give us the batch number on your label.
A document that lacks a batch number, a test date or the laboratory's name is not a batch record. Our lab tests page explains what to look for.
Where to buy retatrutide in the UK: how to check a supplier
Whichever shop you buy retatrutide from, check these five points before you order:
- A batch number and a certificate for that batch. The pack should carry a batch number, and the seller should be able to show a certificate of analysis for that same batch from a named laboratory, with the test date. Every Free Muscle-brand batch is assayed by Janoshik Analytical, and we send the certificate for your batch on request.
- The strength per capsule and the capsule count. With both figures you can work out the total milligrams in the pack and the price per milligram. If a listing does not state one of them, ask the seller before you order.
- Research-use labelling and an age check. A research compound should be sold for laboratory research use only, not for human consumption, to adults aged 18 or over, with no dosing or usage advice. That is how every listing here is sold.
- Prices in pounds sterling and tracked UK dispatch. UK delivery from us is free and tracked on every order, with no minimum spend, and usually arrives 2-3 working days after dispatch; orders placed before 2pm Monday to Friday are processed the same working day.
- A clear returns policy. Unopened items can be returned to us within 30 days.
Brand on this page: Free Muscle. The UK supplier checklist and how we test go into more detail.
Legal status in the UK
Retatrutide is not a licensed medicine in the UK and has no MHRA marketing authorisation, nor does it hold approval from the EMA or FDA. It is an investigational medicine available to patients only within clinical trials. It is not an authorised food supplement and may not be sold for human consumption. It is supplied here for laboratory research to adults aged 18 and over. It is not a controlled drug. Anyone seeking treatment for weight or blood glucose should speak to a doctor, since this is not a treatment and licensed options with clinical supervision exist. For background on how research peptides sit within UK law, see our SARMs versus peptides guide.
In October 2025 the MHRA stated that retatrutide has not been approved for UK use and that, outside authorised clinical trials, any products sold in the UK claiming to contain it are likely to be illegal and potentially dangerous to health; in May 2026 it made arrests at a site producing unlicensed weight-loss medicines, retatrutide among them. Lilly, the developer, states that retatrutide is legally available only to participants in its clinical trials.
Storage and handling
Peptides degrade faster with heat, moisture and light, so keep the container sealed in a cool, dry, dark place, labelled with its batch number and out of reach of children and animals. The product page names the ways peptides degrade and covers handling and disposal.
Delivery and returns
Free Muscle is the trading name of FreeMuscle, a business registered in Andorra, with UK operations and dispatch in Scunthorpe. UK shipping costs nothing, is tracked and comes in plain packaging, and weekday orders that arrive before 2pm are processed on the day; EU delivery takes three to seven working days. Anything unopened can come back within 30 days, and only adults aged 18 or over may order. Terms are on our shipping and guarantee pages.
Related reading
- Retatrutide in the UK 2026: licensing status and trials
- SLU-PP-332 and 5-Amino-1MQ: what the mouse data show
- How to choose a SARMs or peptide supplier in the UK: a checklist
- Do oral peptides actually work? The honest answer
- What is Janoshik Analytical? Third-party testing explained
- How to read a certificate of analysis
- Metabolic support, all peptides and 5-Amino-1MQ
Research compounds sold by Free Muscle are supplied for laboratory research use only and are not for human consumption. They are not authorised as medicines by the MHRA, EMA or FDA, are not food supplements, and are sold only to adults aged 18 or over. Nothing on this page is medical or dosing advice.
Frequently asked questions
Is retatrutide legal in the UK?
Retatrutide is not a controlled drug, but it is an investigational medicine with no MHRA, EMA or FDA approval, so it cannot be prescribed or sold for human consumption. In October 2025 the MHRA warned that retatrutide products sold in the UK outside authorised clinical trials are likely to be illegal and could be dangerous to health, and Lilly says it is legally available only to its trial participants. Free Muscle supplies it for laboratory research and does not sell to anyone under 18.
Is retatrutide approved anywhere?
No. Retatrutide (LY3437943) has no marketing authorisation from any regulator. Phase 2 results were published in 2023 and the first Phase 3 papers in 2026, and Lilly intends to file for US approval in early 2027. UK use outside clinical trials would need MHRA authorisation, which has not been granted. Until then it remains an investigational compound.
Is retatrutide a peptide or a SARM?
Retatrutide is a peptide: an engineered chain of amino acids that acts on three hormone receptors at once. It is not a SARM and has nothing to do with the androgen receptor. It acts on the GIP, GLP-1 and glucagon receptors, which regulate appetite, insulin release and energy expenditure.
What is the difference between retatrutide and the licensed GLP-1 medicines?
Licensed GLP-1 medicines act on the GLP-1 receptor alone or on GLP-1 and GIP together. Retatrutide adds glucagon receptor agonism as a third action. It has not been through the full regulatory process those medicines completed, and it is not an alternative to them. Anyone seeking treatment should speak to a doctor.
Does retatrutide work in capsule form?
The published trials used subcutaneous injection only. Peptides of this size are largely broken down in the gut, and no published study shows that an oral capsule reproduces the trial results. We make no claim that it does, and nothing on this page should be read as suggesting otherwise.
Is retatrutide detectable in sport drug tests?
The WADA Prohibited List does not name retatrutide individually, but section S0 of the 2026 List bans at all times any substance not covered elsewhere on the List that has no current approval for human therapeutic use, which includes drugs in clinical development. No published study gives a detection window. Any tested athlete should regard it as prohibited and confirm the position with the current List and their governing body.
How do I verify the batch of retatrutide I receive?
Retatrutide on this page is Free Muscle brand, and each batch goes to Janoshik Analytical, an independent laboratory, for assay. To see the result for your pack, send us the batch number from the label by email and we will return the certificate for that batch. Because the compound is new, check the identity method, the purity figure and the laboratory name on the certificate before relying on it.
Which retatrutide strength should I choose?
We do not make that recommendation for any product, and retatrutide is no exception: it is supplied for laboratory research only and this page is not guidance on selection or use. The listing text does not yet state the strength per capsule or the capsule count, so the Janoshik batch certificate, available on request, is the reference for what a given batch contains.
Where can I buy retatrutide in the UK?
On this page you can compare every retatrutide listing we stock (at present from Free Muscle). Every UK order ships free with tracking, with no minimum spend, and usually arrives 2-3 working days after dispatch. Everything here is supplied for laboratory research use only, not for human consumption, to adults aged 18 or over.
How fast is UK delivery?
UK delivery is free and tracked on every order, with no minimum spend, and usually arrives 2-3 working days after dispatch. Faster tracked UK delivery costs £6 and usually takes 1-2 working days. Orders placed before 2pm Monday to Friday are processed the same working day.
Do you deliver to Romania and the rest of the EU?
Yes. Orders to Romania and other EU countries travel by our paid, tracked international service and usually arrive 3-7 working days after dispatch; delivery to the rest of the world usually takes 5-14 working days. Prices are in pounds sterling (GBP). Rules differ in other countries, so check local law before ordering for delivery abroad.
Can I return an order?
Yes: unopened items can be returned within 30 days. Our guarantee page has the full policy.
Is there a discount when I buy more than one?
Yes, on Free Muscle-brand products: 5% off automatically when your cart holds 2 of them and 10% off with 3 or more, applied in the cart. The offers do not combine.