In February 2026 the MHRA published a safety alert after Eli Lilly identified five falsified Mounjaro KwikPen 15mg pens, all carrying batch number D873576, supplied by a single pharmacy in Birmingham.
Two details make this case worth understanding rather than just fearing. First, the fakes did contain tirzepatide — but because the manufacturing conditions were unknown, the MHRA could not confirm the contents were sterile. Second, they were spotted because the pens physically failed: in almost every case, the dose knob came off during use.
The Uncomfortable Part
These pens were not bought from a social media seller. They reached patients through a registered pharmacy. That matters because the standard advice — "only use a registered pharmacy" — is correct and necessary but is not, on its own, a complete defence.
The defence that worked here was patients noticing something wrong with the device and reporting it.
What to Check on Your Pen
- Batch number and strength. Both are printed on the pen and the carton. In this case only 15mg pens with batch D873576 were affected; a 15mg pen with a different batch number was fine to continue using.
- Packaging quality. Misaligned printing, spelling errors, unusual fonts, a carton that opens differently from previous ones, missing or damaged tamper seals.
- The patient information leaflet. Poor translation, odd formatting or a missing leaflet entirely.
- The device itself. Parts that feel loose, a dose dial that does not click firmly, anything that comes away in your hand.
- The liquid. It should be clear and colourless to slightly yellow. Cloudiness or particles mean do not use it.
- Expiry date — check it against the carton, and check the carton against the pen.
Where the Real Risk Concentrates
The MHRA has been warning about pens sold outside the legitimate supply chain for years, and has seized hundreds of suspected fake semaglutide pens. In some cases people were hospitalised, with symptoms including hypoglycaemic shock — a pattern suggesting the pens contained insulin rather than the medicine on the label.
Insulin in someone who is not diabetic and not expecting it is genuinely dangerous. This is the reason "cheaper on a marketplace app" is not a saving.
Buying Safely
- Use a UK-registered pharmacy. You can check the register rather than trusting a logo on a website.
- Expect a real clinical assessment. Since 2025 the GPhC has required online pharmacies to independently verify weight, height and/or BMI before supplying weight-management medicines, and to offer two-way communication with the prescriber.
- Treat an unusually low price as a question, not a bargain.
- Never buy from social media, messaging apps or a marketplace listing.
If You Think You Have a Fake
Stop using it immediately. Report it to the MHRA through the Yellow Card scheme, and contact the pharmacy that supplied it. Keep the pen and packaging — the batch number is the piece of evidence that lets a recall be scoped.
If you have already injected from a pen you now suspect, contact a healthcare professional for advice. In the 2026 Mounjaro case the assessed risk to those who had already used the affected pens was low, but that is a judgement for a clinician with your details, not a reassurance to apply yourself.