Of the 10,000 deaths caused by adverse reactions to prescription drugs every year, a “significant number” were likely to have been caused by patients mixing their treatments with complementary medicines, doctors’ leaders said yesterday.

Research has shown that more than 90 per cent of people prescribed drugs such as warfarin, a powerful anti- coagulant taken to stop the build-up of lethal blood clots, were not asked by their GPs if they were taking any complementary medicines.

Popular substances such as St John’s wort, a plant extract taken for mild depression, have been found to react dangerously with warfarin and other prescription drugs, preventing the treatments from working.

In the study, published in the British Journal of General Practice (BJGP), one in five patients on warfarin was found to be taking complementary medicines also.

Lindsay Smith, the lead author of the report, said that the findings raised serious concerns about the lack of communication between doctors and patients about herbal remedies. Current software used by GPs to compile patient records does not include a facility to record data on alternative medications.

“What was really striking was that one in five people is taking something and nine out of ten are not discussing it with their doctor,” Dr Smith, a GP in Somerset, said.

“If complementary medicines were perfectly safe and had been thoroughly tested, there wouldn’t be a problem. But most of these medications remain untested and unresearched. This is potentially very dangerous.”

In the research carried out by Dr Smith, 1,360 patients taking warfarin from 35 different practices were surveyed about herbal remedy use. Almost 300 were found to be taking a listed complementary medicine, of which 25 were taking at least one reported to react with warfarin, such as St John’s wort, ginseng or gingko biloba, a tree leaf extract believed to improve blood flow to the brain. A further 200 patients were on other unidentified alternative medicines. Dr Smith said that problems arise from the lack of medical knowledge of interactions between prescription and alternative medicines. His group is to undertake further research into gingko and garlic pills.

It is estimated that at least 12 million Britons regularly use herbal remedies, while more than 500,000 take warfarin. The overlap, which remains undocumented, is likely to be high among the elderly, who often rely on multiple medications for different ailments, health experts said.

The report follows the publication yesterday of research from scientists at the University of Liverpool which estimates that more than 10,000 patients may be dying every year because of reactions to common medications such as aspirin, anticoagulants and antidepressants.

Researchers said that while most cases had been attributed to conventional drug reactions — with patients and GPs asked about St John’s wort usage — other herbal remedies were likely to have contributed to the high death rate.Concerns have been raised about the effects of echinacea, a popular anti-viral supplement, on the liver when combined with other drugs, and garlic supplements on some anti-HIV treatments Jim Kennedy, the Royal College of General Practitioners spokesman on prescribing, said that adverse reactions triggered by herbal remedies would be high.

“It is going to be a factor in a significant number of those deaths — certainly in the hundreds,” he said.

Edzard Ernst, director of the Department of Complementary Medicine at the University of Exeter and an adviser on the BJGP report, said that many British GPs “ know absolutely nothing about complementary medicine”.

“But they have a moral duty to advise patients responsibly on all matters of healthcare. To exclude a whole strain of healthcare and say it’s got nothing to do with us because we didn’t learn it at medical school is not responsible.”

He added: “With a drug like warfarin the therapeutic window is very narrow. Underdosing you can have a blood clot, and overdosing can lead to extensive bleeding and, in worst -case scenarios, brain haemorrhages. You are dead as a church mouse. Any interference with herbal medicines is potentially life-threatening.”

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