St John's Wort can interfere with hormones

Scientists at London's Homerton Hospital Hospital warn remedies such as garlic, cod liver oil and St John's Wort pose a risk of side effects.

However, a survey of more than 300 cancer patients found more than half took herbal remedies or food supplements.

The research is published in the British Journal of Cancer.

There is a tendency to believe that complementary medicines are always harmless. This is not the case. Professor Robert Souhami

The survey also revealed that fewer than half those taking complementary medicine had discussed this with the doctor overseeing their conventional treatment.

Around one third of those patients were unsure of the purpose of the remedy they were taking.

And 11% of patients reported taking supplements higher than the recommended doses.

Bad reactions

Earlier research has shown that some complementary medicines have dangerous side effects and may react badly with conventional treatments.

For instance, garlic and cod liver oil are anticoagulants and may exaggerate the effect of blood thinning drugs taken by some cancer patients.

Garlic can thin the blood

Remedies such as St John's Wort can interfere with the action of hormones, antibiotics and chemotherapy.

Researchers were also concerned about echinacea which has effects on the immune system and may compromise some types of cancer treatments for lymphoma and leukemia.

Lead researcher Dr Ursula Werneke said the new study highlighted the need for doctors to discuss complementary medicine with their patients - and to ensure they were fully briefed on how remedies interact with standard treatment.

She said: "The real problem is that doctors may not have the expert knowledge needed to deal with so many potential risks when patients are mixing conventional treatment with alternative remedies.

"They need to avoid uncritical encouragement. Also there is not always time to discuss it in routine outpatient clinics.

"As well as this patients will not always accept their doctors' opinions and may argue that conventional cancer treatment is equally toxic."

Most popular

Among the most common remedies, taken by the patients in the study, were echinacea, evening primrose oil, and gingko.

The most popular supplements were combinations of vitamins, cod liver oil and selenium.

The study revealed that more than 12% of patients had been given health warnings from pharmacists and these mostly concerned lymphoma patients who were taking echinacea which can interfere with antibody treatment.

Further warnings were given to individual patients for cod liver/fish oil, gingko, garlic, kava kava and beta-carotene.

Professor Robert Souhami, of the charity Cancer Research UK, said: "There is a tendency to believe that complementary medicines are always harmless. This is not the case.

"This research is very valuable in that it indicates more work needs to be done to get a clearer picture about how complementary medicines react with conventional drugs so patients can receive the best possible advice concerning their treatment."