Scientists have warned of the dangers of taking herbal and dietary supplements (HDS) while on any kind of medication.

Mixing supplements with many kinds of medicines, particularly those aimed at the cardiovascular and central nervous systems, could result in harmful drug interactions, they insisted.

The Asian scientists carried out a detailed analysis of 31 studies and 54 review articles on this topic. These included information on 213 supplements, 509 prescribed medications and almost 900 HDS-drug interactions.

"Our extensive review clearly shows that some HDS ingredients have potentially harmful drug interactions that are predominately moderate in their severity.

"It also showed that herbal and botanical remedies were more likely to have documented drug interactions and contraindications than the other dietary supplements, such as vitamins, minerals and amino acids," the scientists from the China Medical School in Taiwan said.

Two of the drugs with the highest number of HDS interactions were the anti-clotting drug, warfarin and insulin, which is used to treat diabetes.

Meanwhile, in almost half of all the cases assessed, the interaction was caused by the supplement altering the way in which the prescribed drug worked in the body.

At least one in four of the interactions were described as major.

Details of these findings are published in the International Journal of Clinical Practice. In an editorial, Prof Edzard Ernst, of the University of Exeter, noted that ‘large proportions of the population' are using HDS and most experts therefore acknowledge that there is a substantial risk of interactions.

"However despite this consensus and despite the considerable amount of documented harm generated by such interactions, our current knowledge is still woefully incomplete," he said.

He added that every doctor should ‘routinely include questions about alternative medicine use in their medical history taking'.