Retatrutide UK: research peptide 40 mg vials

What is retatrutide?

Retatrutide (LY3437943) is an investigational 39-amino-acid peptide carrying a C20 fatty diacid side chain. It is a triple agonist: it activates the GLP-1, GIP and glucagon receptors at once, which is what separates it from semaglutide (GLP-1 only) and tirzepatide (GLP-1 and GIP). It was designed by Eli Lilly and is in phase 3 clinical trials for obesity, type 2 diabetes, obstructive sleep apnoea and knee osteoarthritis. It has no marketing authorisation in any country.

We supply the synthetic retatrutide peptide in the UK as a lyophilised research reagent at 99%+ HPLC purity, in sealed 40 mg vials, with a certificate of analysis for every lot. It is a laboratory reagent for in-vitro research and is never supplied for human use.

Retatrutide vials, sizes and price

Retatrutide for sale on this page comes as a single vial size: 40 mg of lyophilised peptide at £149.99, which is £3.75 per mg. That is the size the compound is most often supplied in for research, it gives the lowest retatrutide price per milligram we can offer, and a 40 mg vial reconstituted in the laboratory covers an extended in-vitro programme from one lot. Prices include VAT; delivery is free over £100 so every retatrutide order ships free.

The retatrutide cost per milligram here is a research-reagent price. It is not comparable with a licensed medicine price, and no part of it is priced for human use. Bank transfer and card are accepted; orders placed before 1pm Monday to Friday leave the same day.

Retatrutide pen or vial?

Searches for a retatrutide pen turn up prefilled injector pens sold by grey-market websites. We do not sell retatrutide pens, and there is no licensed retatrutide pen anywhere in the world: the only pens that exist are the ones used inside Eli Lilly's trials. A prefilled pen is a drug-delivery device, which is a medicine by definition. A research vial is different: it holds a weighed mass of lyophilised peptide, sealed under an aluminium crimp, to be reconstituted in a laboratory for analytical or in-vitro work. If a seller offers a retatrutide 40 mg pen, ask what regulatory status they claim for it, because it cannot be a research chemical.

Retatrutide vs Mounjaro (tirzepatide) and semaglutide

Retatrutide vs Mounjaro is the comparison most people are searching for, so here is how the three compounds differ on the published record. Mounjaro is the brand name for tirzepatide, a licensed prescription medicine that acts on the GLP-1 and GIP receptors. Wegovy and Ozempic contain semaglutide, a licensed GLP-1 receptor agonist. Retatrutide adds the glucagon receptor to both, and is unlicensed.

On trial data, the phase 2 retatrutide study published in the New England Journal of Medicine in 2023 reported a mean body-weight reduction of 24.2% at 48 weeks in the highest-dose arm. The SURMOUNT-1 trial of tirzepatide reported 20.9% at 72 weeks, and the STEP 1 trial of semaglutide reported 14.9% at 68 weeks. These figures come from different trials with different populations and durations, so retatrutide vs tirzepatide is not a head-to-head result; Lilly's phase 3 TRIUMPH programme is what will settle it. None of this is a claim about our product, which is supplied for laboratory research only.

Retatrutide side effects reported in trials

The retatrutide side effects reported in the phase 2 trial were dose-dependent and mostly gastrointestinal: nausea, diarrhoea, vomiting and constipation, largely mild to moderate and most frequent while the dose was being escalated. Increases in heart rate were observed, along with skin sensitivity (dysaesthesia) in a minority of participants, and some withdrew because of adverse events. These are trial observations in a controlled clinical setting and are reproduced here for completeness of the scientific record. They are not a safety profile for any product on this site, and we do not give any guidance on human use.

Where to buy retatrutide online in the UK

Where to buy retatrutide online comes down to what a supplier can prove. Check for a certificate of analysis tied to the lot number on the vial (identity by mass spectrometry, purity by HPLC), sealed crimp-capped vials rather than loose or repackaged stock, cold-chain storage, UK dispatch rather than drop-shipping from overseas, and a research-use policy that is actually enforced. Be wary of any seller who describes retatrutide as a weight-loss product or a pen, publishes dosing schedules, or quotes a price per month rather than per milligram: those are the hallmarks of a supplier marketing an unlicensed medicine for human use, which is unlawful in the UK.

Our retatrutide vials are stocked in the UK, tested per lot, shipped in plain insulated packaging with a cool pack, and sold under a research use policy that we apply to every order.

Legal and regulatory position

Retatrutide is not a controlled substance in the UK and is legal to possess. It is an investigational medicine with no licence in any country; its licensed relatives semaglutide and tirzepatide are prescription-only. The MHRA actively pursues unlawful supply of GLP-1-class medicines for human use. This product is sold as a laboratory reagent on the basis of written legal advice, and is not supplied for human use under any circumstances. Correspondence indicating an intended human use results in the order being refused.

Sizes and pricing

• Retatrutide 40mg: £149.99 (£3.75/mg). SKU RETA-40.

Prices include VAT. Shipping is £4.95 by Royal Mail Tracked 24, free on orders over £100. Ships from UK stock with the lot certificate for the vial you receive.

Quality and testing

Each lot of Retatrutide is sent to an independent UK laboratory before release for identity by mass spectrometry, purity by HPLC, residual solvents and bacterial endotoxin. The lot number on the vial label matches the certificate on our certificates page, and no lot is released for sale until the certificate is in hand. Specification: ≥ 99% (HPLC), supplied as lyophilised powder, 3 ml glass vial, sealed, 40 mg per vial.

Reconstitution and handling

Retatrutide arrives as a lyophilised cake under an aluminium crimp seal. Let the vial reach room temperature before opening so that condensation does not form on the powder. Swab the stopper with an alcohol swab, draw the chosen volume of bacteriostatic water with a sterile syringe, and add it slowly down the inside wall of the vial rather than onto the powder. Swirl gently until clear; never shake, which can denature the peptide. Label the vial with the date and concentration. The peptide calculator converts vial amount and diluent volume into concentration, millilitres and U-100 syringe units for any target amount. Sealed vial: 2 to 8 °C, protected from light. Reconstituted: 2 to 8 °C, use within 4 weeks.

Lot traceability

Every Retatrutide vial carries a printed lot number and expiry. The same lot number appears on the certificate of analysis for that batch, which names the testing laboratory and the report number so it can be verified directly. If the number on your vial does not match a certificate on our site, contact support before using it. Certificates are kept online for the life of the product plus two years.

Related products

BPC-157, TB-500, Wolverine Stack, and everything else in Weight & Metabolic or the full range. Reconstitution supplies: bacteriostatic water, insulin syringes and alcohol swabs.

Handling and storage

Sealed vial: 2 to 8 °C, protected from light. Reconstituted: 2 to 8 °C, use within 4 weeks. Keep sealed until use. Allow the vial to reach room temperature before opening to avoid condensation on the powder. Reconstitute with bacteriostatic water added slowly down the wall of the vial; do not shake. Our calculator covers the arithmetic.