Thousands of packets of St John’s wort tablets have been recalled in the UK as a safety precaution after some were found to be contaminated with a toxin which could cause human liver damage.

Health regulators issued an urgent recall of six batches of the herbal treatment – 91,800 packets in total – which have been on sale since September 2013 and are due to expire between May and August 2016.

St John’s wort is extracted from the hypericum perforatum plant, and is typically used to treat depression, anxiety, loss of appetite and insomnia.

The affected tablets, manufactured for Superdrug, Asda and alternative treatment specialist HRI Herbal Medicine, were found to be contaminated. The Medicines and Healthcare products Regulatory Agency (MHRA) has warned that the affected batches have levels of a toxic pyrrolizidine alkaloid above the threshold recommended by the Committee on Herbal Medicinal Products, a European expert body. The St John’s wort in the recalled tablets was likely to have been mixed with poisonous weeds when the plants were harvested, the MHRA said.

The MHRA is urging consumers to check their medicine cabinets to see if they have any of the affected batches, although it stressed the recall was a precautionary step and that it had so far not received any reports of health problems arising from the affected tablets.

Gerald Heddell, director of inspection, enforcement and standards at MHRA, said: “If you have one of these packs don’t take the tablets any more and return them to the Herbal Research Company.”

Pyrrolizidine alkaloids can cause liver problems in humans. Symptoms include yellowing of the whites of the eyes and/or skin, nausea, vomiting, dark urine, abdominal pain and unusual tiredness. Consumers who have taken the tablets and experienced any of these symptoms should notify their doctor immediately.

The affected batches contain 30 tablets per pack and are: Asda St John’s wort (batch number 14279), Superdrug St John’s wort (batch 14523) and HRI Good Mood (batches 14255, 14662, 14498, 14660).

• Consumers can contact the Herbal Research Company on 01934 838 820 or email recall@QP-Services.com to receive a pre-paid return envelope