How to avoid fake weight loss injections in the UK

What the MHRA has found

The Medicines and Healthcare products Regulatory Agency is the UK body that licenses medicines and investigates fakes. Its guidance on GLP-1 medicines, updated 5 February 2026, states the only way to guarantee a genuine GLP-1 medicine is to obtain it from a legitimate pharmacy with a valid prescription. It reports counterfeit pre-filled pens closely mimicking licensed products, and severe side effects reported after fake products were used. It also says legitimate GLP-1 medicines come as pre-filled pens or tablets, and products sold as a powder in a vial for mixing are not authorised.

On 24 February 2026 the MHRA issued a Drug Safety Update on falsified Mounjaro KwikPen 15 mg pens carrying batch number D873576. They were supplied through one UK online pharmacy and five pens were identified. Testing found tirzepatide in the pens but sterility could not be assured, and every pen had a faulty mechanism, with the dose knob often coming off in use. The batch number is genuine for 7.5 mg pens, which are not affected. The MHRA told patients with a 15 mg pen bearing that number not to use it and to email info@mhra.gov.uk with Mounjaro Pens in the subject line.

The case shows a fake can reach a patient through a registered pharmacy's supply chain, which is why batch checks matter alongside source checks.

Who is at risk

Anyone buying a GLP-1 medicine outside the registered pharmacy system. The MHRA names beauty salons and social media as sources to avoid. Anyone offered a pen without a prescriber consultation is being offered an illegal supply, because every GLP-1 medicine is prescription only and GOV.UK states a consultation has to happen before a prescription is issued. The rules apply in all four UK nations. In England, Scotland and Wales the pharmacy has to be on the General Pharmaceutical Council register. In Northern Ireland it has to be on the Pharmaceutical Society of Northern Ireland register.

The price floor as a warning sign

Genuine supply has a floor. GLP Index tracked 80 registered pharmacies for Mounjaro on 21 October 2026 and the cheapest first order was £88.00 at 2.5 mg, £120.00 at 5 mg, £168.00 at 7.5 mg, £188.00 at 10 mg, £202.00 at 12.5 mg and £219.00 at 15 mg. The cheapest ongoing prices ran from £105.00 to £234.00. For Wegovy across 72 pharmacies the cheapest first order was £44.00 at 0.25 mg and £112.00 at 2.4 mg, with ongoing prices from £74.00 to £199.88. For the Wegovy pill the floor was £53.00 at 1.5 mg, and for Foundayo £46.00 at 0.8 mg.

These are the lowest prices any registered pharmacy charged after a consultation, with delivery included. A seller offering a 15 mg Mounjaro pen for half of £219.00, or a 2.4 mg Wegovy pen for half of £112.00, is below the cost of genuine supply. The price is the first sign that what is on offer is not a licensed product obtained legally.

Steps to buy safely

1. Find the pharmacy's GPhC registration number on its website, usually in the About us section or the footer. The GPhC says if a pharmacy is not listed, do not use it.
2. Search the GPhC register by name or number and check the premises address matches the website.
3. Complete a consultation with a prescriber before any order. A site that sells without one is breaking the law.
4. Check the MHRA warning signs listed by the GPhC: an unusual web address, poor design and spelling errors, claims such as 100 per cent safe or no side effects, prescription medicines and prices on the home page, no prescription required, payment in cryptocurrency, a request not to name the medicine in your bank reference, and no street address.
5. Compare the price against the floor on the Mounjaro, Wegovy, Wegovy pill and Foundayo price pages. Anything well below the cheapest registered pharmacy is a red flag.
6. When the pen arrives, check it is a sealed pre-filled pen or a tablet pack, not a vial of powder. Check the batch number against any current MHRA alert.
7. Keep the box, batch number, invoice and the pharmacy's name until the supply is finished.

If you think you have a fake

Do not use the product. Report it to the MHRA through the Yellow Card scheme, which takes reports of suspected fake or falsified medicines as well as side effects. Reports can be made on the Yellow Card website or the Yellow Card app on the Apple App Store or Google Play. Include the product name, dose, batch number, where you bought it and any symptoms.

If you have already injected and have unusual symptoms, the MHRA advises seeking immediate medical attention. For the falsified 15 mg batch it said the risk to patients who had already injected was low based on the cases reviewed, but each patient should be assessed for allergic reaction, infection or sepsis.

If you paid by card to a seller outside the registered system, your card provider may be able to reverse the payment. Keep every message from the seller.

Mistakes that cost money and health

Buying from a social media account or messaging app because it is cheaper than any pharmacy. Buying a pen from an acquaintance who has spare supply, which is an unlawful supply with no cold chain. Buying a vial of powder marketed as the same ingredient. Choosing a website because the home page shows pen prices and promises next-day delivery with no questions asked. Ignoring a batch alert because the pen looks right.

Where the figures come from

The MHRA position on legitimate supply, counterfeit pens and powders in vials is from the GOV.UK guidance on GLP-1 medicines. The falsified Mounjaro details are from the MHRA Drug Safety Update of 24 February 2026. The register check and warning signs are from the General Pharmaceutical Council. Price floors are from the GLP Index export of 21 October 2026.