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What is retatrutide and is it legal in the UK?

GLP Guidebook teamUpdated 12 Oct 202612 sourcesWritten from published sources
The short answer

Retatrutide is not licensed in the UK, or anywhere, as of October 2026. It is Eli Lilly's experimental weekly injection that acts on the receptors for three hormones, GIP, GLP-1 and glucagon. The MHRA says products sold in the UK claiming to contain it are likely illegal and potentially dangerous. Lilly says it is available only in its clinical trials.

Before you go further
  • Retatrutide is not a licensed medicine anywhere. Lilly, its maker, says it is available only to people in its clinical trials.1
  • The GLP‑1 medicines that are licensed in the UK are prescription-only.12
  • The risks of this family of medicines are in Guide 5: Side effects and risks.
  • Nothing here promises any result.

How does retatrutide work?

Retatrutide is one molecule that switches on the body's receptors for three hormones, GIP, GLP‑1 and glucagon, so Lilly calls it a triple agonist.1

In trials it is injected under the skin once a week, at 4, 9 or 12 mg.2 Guide 2 explains how GLP‑1 medicines work.

What did the main trial find?

On the top 12 mg dose, adults without diabetes lost 28.3% of their weight on average over 80 weeks, against 2.2% on a dummy injection.2

That trial, TRIUMPH‑1, had 2,339 adults with obesity, or overweight plus a weight-related condition.2 Counting everyone who started, including those who stopped, 12 mg gave 25.0% against 3.9%.2 For someone starting at 90 kg (14 st 2 lb), 25.0% is about 22 kg (3½ st). That is an average, and one person's result can differ. The full results appeared in the New England Journal of Medicine on 29 Sep 2026.3

RisksThe risks, in brief
  • Stomach effects are common. On 12 mg, 42 in 100 people felt sick, against 15 in 100 on a dummy injection; 25 in 100 vomited, against 5 in 100.2
  • Odd skin feelings (dysesthesia) in 13 in 100 people on 12 mg, against 1 in 100 on a dummy injection.2
  • Stopping. 11 in 100 people on 12 mg stopped because of side effects, against 5 in 100 on a dummy injection.2
  • Heart rate rose with the dose in the earlier phase 2 trial, peaking at 24 weeks and then easing.5
Full detail in Guide 5: Side effects and risks →

Is retatrutide legal in the UK?

It has no UK licence, and the MHRA says UK products claiming to contain it are “likely to be illegal” and potentially dangerous.6

In October 2025 the MHRA raided what it called the first illegal factory for weight-loss medicines found in the UK, in Northampton. Officers seized "more than 2,000 unlicensed retatrutide and tirzepatide pens".6 In May 2026 a raid near Northampton found about 12,000 doses, including retatrutide, the MHRA's largest seizure of its kind. Two men were arrested under the Human Medicines Regulations 2012.7

The MHRA says such products have "no guarantees about what they contain", and some may be contaminated.6 It also says powders in vials that you mix before injecting are not authorised.8 The arrests we found were for making and supplying it. We found no MHRA statement on owning it for your own use. See Fake Mounjaro and illegal jabs.

Get help now: call 999 for sudden or severe stomach pain, or if you can't breathe, after injecting anything sold as retatrutide.11 The MHRA asks people to report side effects to the Yellow Card scheme.7

Is retatrutide being tested in the UK?

Yes. UK hospitals and clinics have taken part in Lilly's trials, and a heart and kidney trial with UK sites is still running.9,10

ClinicalTrials.gov lists 9 UK sites in TRIUMPH‑1, which has finished.9 The heart and kidney trial lists 18 UK sites and is active but no longer recruiting.10 Lilly plans to apply for US approval in early 2027.4 We found no UK application date.

Read the full picture

Related questions

Is it safe to buy Mounjaro online in the UK? Is Zepbound available in the UK? Is the Wegovy pill available in the UK? How do I report a side effect to the Yellow Card scheme?
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Sources

  1. Eli Lilly. What to know about retatrutide (FAQ), last updated September 2026. lilly.com
  2. Eli Lilly. Lilly's triple agonist, retatrutide, delivered powerful weight loss in pivotal Phase 3 obesity trial (TRIUMPH‑1 topline). Press release, 21 May 2026. prnewswire.com
  3. Jastreboff AM, Kaplan LM, Davies MJ, Wilding JPH et al. Retatrutide, a triple hormone receptor agonist, for treatment of obesity (TRIUMPH‑1). NEJM, published 29 Sep 2026. doi:10.1056/NEJMoa2604169
  4. Eli Lilly. Lilly's triple agonist, retatrutide, delivered substantial weight loss and A1C reduction (TRIUMPH‑2). Press release, 29 Sep 2026. prnewswire.com
  5. Jastreboff AM et al. Triple-hormone-receptor agonist retatrutide for obesity: a phase 2 trial. NEJM 2023;389:514-26. doi:10.1056/NEJMoa2301972 · PMID 37366315
  6. MHRA. MHRA smashes major illicit weight loss medicine production facility in record seizure. Press release, 24 Oct 2025. gov.uk
  7. MHRA. Two arrested during the MHRA's largest ever seizure of unlicensed weight loss medicines. Press release, 29 May 2026. gov.uk
  8. MHRA. GLP-1 medicines for weight loss and diabetes: what you need to know. Published 5 Jun 2025, updated 5 Feb 2026. gov.uk
  9. ClinicalTrials.gov. A Study of Retatrutide (LY3437943) in Participants Who Have Obesity or Overweight (TRIUMPH‑1), NCT05929066. Completed; 9 UK sites listed, checked 12 Oct 2026. clinicaltrials.gov
  10. ClinicalTrials.gov. The Effect of Retatrutide Once Weekly on Cardiovascular Outcomes and Kidney Outcomes in Adults Living With Obesity (TRIUMPH‑Outcomes), NCT06383390. Active, not recruiting; 18 UK sites listed, checked 12 Oct 2026. clinicaltrials.gov
  11. NHS. Stomach ache (page last reviewed 26 May 2023). nhs.uk
  12. MHRA. First GLP-1 tablet for weight loss approved in the UK. Press release, 11 Jun 2026 ("As with all GLP-1 receptor agonists, this is a prescription-only medication"). gov.uk

Last checked 12 Oct 2026 · Next review due 12 Apr 2027 · Report an error

How this answer was made. Written by the GLP Guidebook team from the sources above. It's general information, not medical advice. Talk to a qualified doctor before starting, stopping or changing any medicine. How we write