Regulators have issued a warning over a contaminated weight loss pill sold on the internet and in Chinese medicine shops.

The Medicines and Healthcare products Regulatory Agency said people should avoid a product called Herbal Flos Lonicerae (Herbal Xenicol) Natural Weight Loss Formula due to concerns over possible side effects.

People taking this product should stop immediately and contact their family doctor or another health worker.

The warning comes after a GP reported a case of a patient being hospitalised and several others suffering a range of side effects including palpitations, severe gastritis, abdominal pain and insomnia after taking the capsules.

The drug is thought to contain a pharmaceutical substance, the identity of which has not yet been established. Tests are currently under way in the laboratory to work out what could be causing the side effects.

MHRA head of herbal medicine policy, Richard Woodfield, said: “Since 2005, the MHRA has found over 280 examples where so-called ‘herbal’ or ‘natural’ products have been adulterated with random quantities of powerful pharmaceutical substances.

“Such products pose a real risk to the public.

“It is because of situations such as this one that the Traditional Herbal Registration scheme is being introduced and why EU legislation has been changed in order to regulate herbal medicines.

“People have a right to know that what they are putting into their bodies to treat one condition will not directly cause a possibly more severe one simply as a result of very poor practice in parts of the sector.

“The THR scheme will make it possible to give people clear advice on which herbal products are safe to use, and provide an assurance that they were made in adequate conditions, and to the necessary standard.”