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How do you spot fake Mounjaro or an illegal weight-loss jab in the UK?

What the MHRA has seized since 2023, and the falsified Mounjaro 15 mg batch. Plus why retatrutide is illegal to sell, and what to do with a pen you doubt.

GLP Guidebook teamPublished 12 Oct 20265 min read14 sourcesWritten from published sources

Written for the UK. Reading from India? India version

The short answer

Often you can’t by looking: the MHRA warns that some fakes closely copy real pens. Its test is the source: a registered pharmacy, a prescription and a proper check. Warning signs include no prescription, powder in vials, salon or social-media sellers, and anything sold as retatrutide, which is not authorised in the UK.

Key takeaways

  • The MHRA warns that counterfeit pens can closely mimic licensed ones, so the safest check is where a pen comes from, not how it looks.1
  • In February 2026, 5 falsified Mounjaro 15 mg pens, batch D873576, were found from one UK online pharmacy; in all but one, the dose knob came off in use.2
  • Fake Ozempic pens seized in 2023 put some people in hospital with very low blood sugar, suggesting they held insulin, not semaglutide.3
  • The MHRA seized more than 5,000 illegally traded GLP-1 products in 2025, then about 12,000 doses in one raid in May 2026.4,5
  • Retatrutide is not authorised in the UK, so the MHRA says anyone selling it is doing so illegally.6
Before you go further
  • GLP‑1 medicines are prescription-only medicines in the UK, never sold over the counter.7
  • Ozempic and Rybelsus are licensed for type 2 diabetes only, not for weight loss.1
  • A prescriber decides whether a medicine fits, which one and at what dose. Nothing here is a recommendation.
  • The risks are the same however you get it: see our side effects guide.
On this page
  1. What fake and illegal weight-loss products has the MHRA found?
  2. What happened with the falsified Mounjaro 15 mg batch?
  3. Can you tell a fake by looking at it?
  4. What is retatrutide, and why is it illegal to sell?
  5. What can go wrong with a fake?
  6. How do you report a fake or a suspicious seller?
  7. Questions people ask
  8. How we researched this
  9. Sources

What fake and illegal weight-loss products has the MHRA found?

Counterfeit branded pens, pens filled in illegal factories, powder vials and unlicensed medicines such as retatrutide.3,8,1

  • Oct 2023The MHRA had seized 369 suspected fake Ozempic pens since January 2023. Fake Saxenda pens were also reported.3
  • Oct 2025A Northampton warehouse was the UK’s first known illegal weight-loss medicine factory. Officers seized over 2,000 retatrutide and tirzepatide pens and tens of thousands of empty pens.8
  • Jan 2026The MHRA reported more than 5,000 illegally traded GLP-1 products seized in 2025. It disrupted over 1,500 websites and social-media accounts selling medicines illegally.4
  • Feb 2026Falsified Mounjaro 15 mg pens were found from a UK online pharmacy.2 Raids in Lincolnshire and Nottinghamshire seized almost 2,000 doses.9
  • May 2026A raid near Northampton recovered around 12,000 doses, the MHRA’s largest seizure of these products.5

Demand far outstrips NHS supply. NICE says 3.4 million people in England fit its Mounjaro criteria. The NHS aims to reach about 220,000 in 3 years.10 The UK Health Secretary called the sellers criminals peddling jabs “to make a quick buck”.8

What happened with the falsified Mounjaro 15 mg batch?

Five fake Mounjaro 15 mg pens labelled batch D873576 were found from one UK online pharmacy, after their dose knobs came off in use.2

The batch number is genuine on Mounjaro 7.5 mg pens, which are not affected. Only 15 mg pens with that number are fake.2 The expiry date on them is not relevant; check the dose and batch.2

Tests found tirzepatide inside, but the MHRA can’t be sure the pens are sterile. That risks infection or an allergic reaction.2 It had no reports of harm needing treatment, and said the risk to people who used them was low.2

The GPhC placed conditions on the pharmacy.2 We don’t name it, because we never name sellers. If you have a 15 mg pen with that batch number, don’t use it. The MHRA asks you to report it to [email protected], and it will arrange to collect the pen. Never try to get a dose out of a faulty pen.2

Can you tell a fake by looking at it?

Not reliably: the MHRA says counterfeit pens can closely mimic the licensed ones, so check the source before the pen.1

Licensed GLP‑1 medicines come as pre-filled pens or tablets. A powder in a vial that you mix with liquid is not authorised in the UK.1 The licensed brands include Wegovy, Ozempic, Rybelsus, Mounjaro and several liraglutide brands.1

A pen that breaks in use is a warning sign. That is how the 15 mg fakes were found.2 So is any medicine offered without a prescription.6

Our post on getting it from an online pharmacy explains how to check a pharmacy is registered.

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What is retatrutide, and why is it illegal to sell?

Retatrutide is a medicine still in clinical trials; it is not approved in the UK, so selling it outside a trial is likely illegal.8

The MHRA says UK products claiming to contain retatrutide “are likely to be illegal and are potentially dangerous”.8 It warns about online hype, and says there’s no guarantee such products even contain it.6

Retatrutide pens were seized in the October 2025 raid. The MHRA says the sites it raided in 2026 made products including retatrutide.8,9,5 Our answer on what retatrutide is covers the trials.

What can go wrong with a fake?

You can’t know what is inside: fakes have caused dangerously low blood sugar, and pens of unknown origin may not be sterile.3,2

In 2023, some people were hospitalised after using suspected fake pens. Their symptoms, including hypoglycaemic shock and coma, suggested insulin rather than semaglutide.3 The head of the MHRA’s enforcement unit says some illegal products may even contain toxic substances.8

Signs of low blood sugar include headache, drowsiness, weakness, dizziness, hunger, confusion, irritability, a fast heartbeat and sweating.11

Get help now: call 999 if someone is confused, very drowsy or can’t be woken after an injection. 999 is for life-threatening emergencies; if you’re not sure, use NHS 111 (in Northern Ireland, your GP’s out-of-hours service).12

How do you report a fake or a suspicious seller?

Report suspected fakes and side effects to the MHRA’s Yellow Card scheme, online, in its app or by phone.3,13

The Yellow Card scheme collects reports of side effects and of defective, falsified or fake products. Anyone can report.3 The free hotline is 0800 731 6789, Monday to Friday, 9am to 5pm.13

The MHRA’s #FakeMeds campaign has tools to help people buy medicines safely online.3 Tell your GP what you have taken, wherever it came from.14 Our side effects guide explains what to watch for with genuine medicines too.

Questions people ask

How can I tell if my Mounjaro pen is real?

Looks aren’t a reliable test. Check it came from a registered pharmacy on a prescription, and check the batch against MHRA alerts. Report any faulty pen.1,2

Is batch D873576 always fake?

Only on 15 mg pens. The same number is a genuine batch of Mounjaro 7.5 mg.2

Is retatrutide legal in the UK?

It is not authorised in the UK. The MHRA says anyone selling it is doing so illegally.6

Are weight-loss jabs sold in vials legal?

Products supplied as a powder in vials, to be mixed before injecting, are not authorised in the UK.1

What should I do if I injected a pen I now think is fake?

Stop using it and keep it. The MHRA advises urgent medical help for any symptoms that worry you, and a Yellow Card report.2,3

How we researched this

We read every MHRA enforcement release and safety notice cited here, plus the MHRA’s patient guidance, on 12 October 2026.

We don’t name the pharmacy behind the falsified batch, or any seller. We show no photos of pens. UK advertising rules treat images of injection pens in weight-loss content as promotion.

Before you move on

  • Get pens only from a registered pharmacy, on a prescription.
  • Never buy from salons, social media or sellers offering no prescription.
  • Refuse powder in vials and anything sold as retatrutide.
  • Check 15 mg Mounjaro pens for batch D873576.
  • Report a faulty or suspect pen to Yellow Card.
Doctor questionsSide effects and risksSeeing a doctor, and the medicines

More from the UK blog

UKUnited KingdomIs it safe to get Mounjaro or Wegovy from an online pharmacy in the UK?UKUnited KingdomMounjaro side effects, and how to report them on the Yellow Card schemeUKUnited KingdomHow much do Mounjaro and Wegovy cost in the UK, on the NHS or privately?
About GLP Guidebook

The monthly UK update

An independent guide to GLP‑1 medicines. We don’t sell medicines, take drug-company money, earn commissions or link to any provider. Once a month: NHS changes, approvals, list prices and safety alerts. How we write

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Sources

  1. MHRA. GLP-1 medicines for weight loss and diabetes: what you need to know. Guidance, published 5 June 2025, updated 5 February 2026. Link
  2. MHRA. Drug Safety Update: Falsified Mounjaro (tirzepatide) KwikPen 15mg pre-filled pens. 24 February 2026. Link
  3. MHRA. MHRA warns of unsafe fake weight loss pens. Press release, 26 October 2023. Link
  4. MHRA. MHRA seizes illegal medicines worth almost £45m in 2025. Press release, 26 January 2026. Link
  5. MHRA. Two arrested during the MHRA’s largest ever seizure of unlicensed weight loss medicines. Press release, 29 May 2026. Link
  6. MHRA. No summer shortcut for safe weight loss. Press release, 24 July 2026. Link
  7. MHRA. UK first in Europe to authorise orforglipron for weight management and type 2 diabetes. Press release, 10 August 2026. Link
  8. MHRA. MHRA smashes major illicit weight loss medicine production facility in record seizure. Press release, 24 October 2025. Link
  9. MHRA. MHRA disrupts second manufacturing facility suspected to be involved in the manufacture of illegal weight loss medicines. Press release, 25 February 2026. Link
  10. NICE. TA1026, section 4: Implementation (funding variation, 12-year period, 220,000 people, Wales). Link
  11. MHRA. MHRA authorises diabetes drug Mounjaro (tirzepatide) for weight management and weight loss. Press release, 8 November 2023. Link
  12. NHS. When to call 999. Link
  13. NHS inform (Scotland). Prescriptions: reporting side effects (Yellow Card hotline). Link
  14. NHS Cheshire and Merseyside (integrated care board). Tirzepatide (Mounjaro) for obesity: information for patients from 1 April 2026. Link

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

How this post was made. Written by the GLP Guidebook team from the sources above. It’s general information, not medical advice. Talk to your GP, pharmacist or prescriber before starting, stopping or changing any medicine. We don’t sell, prescribe or recommend any brand or provider. How we write