Some weight loss jab users have been urged to check their medication after a pharmacy discovered it may have dispensed fake pens. The Medicines and Healthcare products Regulatory Agency (MHRA) is contacting certain patients to make them aware of a small possibility that they may have been dispensed a fake Mounjaro pen by The Private Pharmacy Clinic in Birmingham. The affected product is the KwikPen 15mg solution for injection with the batch number D873576.

Dr Alison Cave, the MHRA's chief safety officer, said: "Check the batch number and strength of your KwikPen. If you have one of the affected pens, stop using it straight away. Please report it to the MHRA by emailing info@mhra.gov.uk. Please include 'Mounjaro Pens' in the subject line. Keep the pen in a safe place. If you have administered injections using the pen already, please be reassured that, based on the cases reviewed to date, the risk to you is low."

The MHRA said it was notified of the counterfeits by Mounjaro manufacturer Eli Lilly and Company Limited, which received five reports of faulty pens.

It stressed that there had been no reports of patients falling ill after using the jabs, and the counterfeits were identified due to faults with the pens where the dose knob came off while in use.

Dr Cave added: "Testing has confirmed that the identified fake pens do contain tirzepatide, the active substance in Mounjaro, but because the manufacturing conditions are unknown, we cannot confirm that the contents are sterile.

"If you are unsure of how to identify the pen, or are unsure on whether you have administered an affected product and have any questions, please speak to a healthcare professional.

"If you suspect that you've had a side effect as a result of using these affected pens, or suspect it's not a genuine product, or have a defective pen, you can report it to our MHRA Yellow Card scheme.

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"It is important you do not try to extract any of this medicine if a pen is defective in any way.

"If you have a 15mg pen and the batch number is different to D873576, please continue to take the medication as directed by your prescriber."

The MHRA noted that the Mounjaro KwikPen 7.5mg may have the same batch number, however this strength is not affected.

If the pens are not sterile, they could cause an infection. Symptoms of infection include redness, swelling or warmth around the injection site, pain or discomfort, fluid leakage and mild fever, chills, fatigue and sore throat.