- UK status: Investigational. No MHRA marketing authorisation. Cannot be prescribed or dispensed outside a clinical trial.
- What it is: A once-weekly injectable "triple agonist" (GLP-1 + GIP + glucagon) made by Eli Lilly.
- Evidence: In the Phase 3 TRIUMPH-1 trial, the 12 mg dose produced about 28.3% average weight loss at 80 weeks; more trials read out through 2026.
- Why you can't buy it: It has not completed regulatory review anywhere; it is not approved by the MHRA, EMA or FDA.
- Safety alert: "Retatrutide pens" and vials sold online or on social media are unlicensed and illegal — the MHRA has seized thousands from illicit UK production sites.
Is retatrutide available in the UK?
No. Retatrutide is an investigational drug: it is still being tested in clinical trials and has not been through the regulatory approval process needed before a medicine can be sold. In the UK, a medicine can only be prescribed and dispensed once it holds a marketing authorisation (a licence) from the Medicines and Healthcare products Regulatory Agency (MHRA). Retatrutide does not have one.
That has some firm consequences. Because there is no licence, retatrutide cannot be prescribed on the NHS, cannot be prescribed privately by a UK doctor, and cannot be dispensed by any GPhC-registered pharmacy. It also cannot be supplied through the "specials" route (that pathway is for patients whose needs aren't met by licensed medicines — not a shortcut for drugs still in development). The one lawful way to receive retatrutide in the UK right now is by taking part in an authorised clinical trial, which you can search for through the NIHR Be Part of Research service.
What is retatrutide?
Retatrutide is a once-weekly injectable being developed by Eli Lilly. It belongs to the same broad family as Wegovy (semaglutide) and Mounjaro (tirzepatide), but goes a step further: it is a "triple agonist" that acts on three gut-hormone pathways at once — GLP-1, GIP and glucagon. Semaglutide targets one of these (GLP-1) and tirzepatide two (GLP-1 and GIP). The added glucagon action is what has drawn attention, because it is thought to increase energy expenditure alongside the appetite-reducing effects of the other two receptors.
Important: being newer or more potent in a trial does not mean it is safer or right for any individual. It simply means the evidence is still being gathered and the regulators have not yet judged whether the benefits outweigh the risks for general use.
What does the Phase 3 evidence show?
Retatrutide is being studied in Eli Lilly's TRIUMPH Phase 3 programme. The first pivotal obesity results, TRIUMPH-1, were reported by Lilly in May 2026. In that trial of 2,339 adults with obesity or overweight (without diabetes), randomised across four groups, the average weight loss at 80 weeks was:
| Group | Average weight loss at 80 weeks | Reached ≥30% loss |
|---|---|---|
| Retatrutide 12 mg | 28.3% (about 70 lb / 32 kg) | 45.3% |
| Retatrutide 9 mg | 25.9% | 37.9% |
| Retatrutide 4 mg | 19.0% | 15.3% |
| Placebo | 2.2% | 0.5% |
Among participants with a starting BMI of 35 or above who continued into an extension on the maximum tolerated dose (9 mg or 12 mg), average weight loss reached about 30.3% at 104 weeks. These figures come from Eli Lilly's own announcement of the TRIUMPH-1 results, which also states that retatrutide "remains investigational and is legally available only to participants in Lilly's clinical trials."
The earlier Phase 2 obesity trial, published in the New England Journal of Medicine in 2023 (Jastreboff et al., DOI 10.1056/NEJMoa2301972), first flagged the drug's potency: participants on the highest dose lost around 24.2% of body weight at 48 weeks. Lilly has said further TRIUMPH results — including studies in people with type 2 diabetes (TRIUMPH-2) and established cardiovascular disease (TRIUMPH-3) — are due to read out later in 2026.
Why isn't retatrutide approved yet?
New medicines follow a set path: laboratory work, then Phase 1–3 human trials, then submission to regulators (the MHRA in the UK, the EMA in Europe, the FDA in the United States) who review all the data before deciding whether to grant a licence. Retatrutide is still completing its Phase 3 programme, so it has not yet been submitted for, or granted, approval in the UK or anywhere else. Until a regulator reviews the full efficacy and safety data and issues a marketing authorisation, the drug remains investigational and unavailable for prescription.
The grey-market and fake-jab risk
Because retatrutide has generated headlines for its trial results, it is being sold illegally — typically as vials from "peptide" websites labelled "not for human consumption" to dodge medicines law, or as counterfeit pens made in illicit factories. There is no way for a buyer to know what is actually in these products. Seized counterfeit weight-loss products have been found to contain the wrong dose, no active ingredient at all, unapproved experimental compounds, or contamination from non-sterile manufacturing — and, in some international seizures, entirely different substances. The MHRA continues to warn the public against buying any weight-loss medicine from unregulated websites or social media.
This risk is not limited to unlicensed drugs. Even licensed weight-loss medicines are being counterfeited: in February 2026 the MHRA warned about falsified Mounjaro KwikPen 15 mg pens (batch D873576) supplied through one online pharmacy — see the official GOV.UK alert. The safe rule is simple: only obtain weight-loss injections from a UK-registered pharmacy against a valid prescription.
Licensed alternatives you can actually get in the UK
If you are looking at weight-loss injections, the medicines that are licensed and legally available in the UK — always via a registered prescriber — include tirzepatide and semaglutide. Speak to your GP or a registered pharmacist about whether any of these are appropriate for you; they can assess your health properly rather than just taking a payment.
- Tirzepatide (Mounjaro): A dual GLP-1/GIP agonist, licensed for weight management and type 2 diabetes. See our guide to Mounjaro UK availability, price and NHS rollout.
- Semaglutide (Wegovy / Ozempic): A GLP-1 agonist. See Wegovy, Ozempic and semaglutide UK availability.
- Oral GLP-1 (orforglipron): A tablet in development — check its current UK status in our guide to orforglipron UK availability.
- Protecting muscle: All drugs in this class cause some lean-mass loss alongside fat loss — see does Mounjaro or Wegovy cause muscle loss?
Whatever you consider, do not start, source or self-manage any of these medicines outside a proper clinical relationship. If you are struggling with weight or metabolic health, your GP or an NHS weight-management service is the right place to start.
Related reading
Mounjaro (tirzepatide) UK
Availability, the 2025 price rises and the phased NHS rollout.
Wegovy & Ozempic (semaglutide)
UK availability and access for the semaglutide brands.
Orforglipron (oral GLP-1)
Where the weight-loss tablet stands for UK patients.
Track UK medicine availability with MediWatch
We check official DHSC and NHS data daily and alert you if a medicine you rely on is affected by a shortage.
Search shortages free →Official & primary sources: MHRA record seizure of illicit weight-loss medicines (GOV.UK) · MHRA (GOV.UK) · Eli Lilly TRIUMPH-1 Phase 3 results · Jastreboff et al., NEJM 2023 (Phase 2 trial) · MHRA falsified Mounjaro pen alert (GOV.UK) · NIHR Be Part of Research
MediWatch is not medical advice. Always follow your prescription label and ask a pharmacist, GP, specialist, NHS 111, or emergency services if you are unsure or unwell. Data checked daily against official sources.