Buying weight loss medicines safely: how to spot an illegal seller

Demand for weight-management medicines has created a criminal market alongside the legitimate one, and it is not small. In 2025 the MHRA seized illegal medicines worth almost £45 million, including 5,680 falsified or illegal GLP-1 weight-loss pens, and dismantled an illicit manufacturing facility in Northampton ^[1].

This page explains how to tell the difference. It is information, not advice about treatment.

The rule that does most of the work

These are prescription-only medicines. Any seller who will supply one without a prescription is breaking the law — and if they are willing to break that law, the question of what is actually in the pen becomes an open one.

The MHRA’s own phrasing, from its July 2026 campaign, is direct: if you are offered GLP-1 medicines “without the need for a prescription — walk away” ^[2].

How to check who you are buying from

1. Check the GPhC register. Any legitimate UK online pharmacy is registered with the General Pharmaceutical Council and should display its registration number, usually in the footer or on an “about us” page. You can look that number up on the GPhC register ^[4]. If there is no number, that is the end of the conversation.

2. Expect a real consultation. A proper service asks about your medical history, your other medicines, pregnancy plans, and your height and weight in a way it can verify. It must be able to say no. A form that approves everyone is not a safety process.

3. Expect a named prescriber. You should be able to find out who is responsible for the prescribing decision.

4. Be suspicious of the sales pitch. Prescription-only medicines cannot legally be advertised to the public. In June 2026 the MHRA, ASA and GPhC jointly warned that naming these medicines, or using phrases like “GLP-1 tablets” or “the new weight-loss tablets” in advertising — including advertising waiting lists — is likely to breach the advertising code ^[6]. A company promoting a named prescription medicine at you is telling you something about itself.

The warning signs

• No prescription needed, or a “consultation” that is a single tick-box
• Sold through social media, a beauty salon, a gym or a private message
• No GPhC registration number anywhere on the site
• Prices far below everyone else
• Products named that are not licensed in the UK
• No patient information leaflet, or one in another language
• Payment by bank transfer or cryptocurrency only

Unlicensed is not the same as unavailable

Some products sold online are not counterfeits of licensed medicines — they are experimental compounds that no regulator has approved. The MHRA specifically named retatrutide in July 2026 as an example of an unlicensed product being sold illegally in the UK ^[2].

Retatrutide is a genuine investigational medicine in phase 3 trials, with published results that look promising. It is also not licensed anywhere in the world, which means no regulator has assessed its manufacture, its dosing or its long-term safety, and nothing sold under that name online has been checked by anyone. The same applies to any product marketed as “research use only” or sold in a vial for you to draw up yourself.

It has already reached UK patients

In February 2026 the MHRA issued an alert about falsified Mounjaro KwikPens from batch D873576, supplied through a clinic in Birmingham. Five affected pens were identified. Testing found tirzepatide was present, but the dose mechanism failed and sterility could not be assured ^[3].

Sterility matters: an unsterile injection puts material directly under the skin, bypassing every barrier your body has.

If you think you have a fake

• Stop using it.
• Keep the packaging and batch number.
• Report it through the Yellow Card scheme, which takes reports about falsified medicines as well as side effects ^[7], and report the seller to the MHRA ^[5].
• Seek medical advice if you feel unwell, and say exactly what you have taken.

The wider point

The reason people buy from these sellers is usually not recklessness. It is cost, or being turned down, or a long wait. Those are real problems, and the honest answer is that a medicine you cannot verify is not a solution to any of them — it is a different risk wearing the same packaging.

If cost or eligibility is the barrier, that is worth discussing with a GP or a registered pharmacy, including what NHS services exist in your area.

This article is for general information and isn’t a substitute for advice from your own clinician. If you feel unwell, contact your GP or NHS 111. In an emergency, call 999.