Scientists have warned that advice on some alternative medicine websites is potentially harmful and dangerous.

Researchers from Exeter University looked at 13 sites covering alternative or complementary medicine.

It is vitally important that patients seek advice from their doctors before embarking on any alternative therapy

Sir Paul Nurse, Cancer Research UK

They found many sites discouraged patients from using conventional cancer therapies.

They also failed to inform readers about alternative remedies that had been shown to be ineffective.

In addition, they made unsubstantiated claims about herbal medicines or other complimentary therapies.

Overall five of the 13 websites were classified as potentially harmful.

Criticisms

One website was criticised for false claims about chemotherapy, key to treating many cancers. It suggests "women with breast cancer are likely to die faster with chemotherapy than without."

It also states that "of approximately half a million people who die of cancer each year only about two to three per cent actually gain benefit from chemotherapy."

Researcher Katja Schmidt criticised another site for suggesting some herbal medicines could cure cancer.

She said: "With a statement like that a patient might abandon orthodox cancer treatment on the basis of the arguments on this website."

Professor Edzard Ernst who headed the study said: "Cancer patients get confused in the maze of claims and counter-claims and often turn to the internet for information which can give advice that has led to real harm and even death in some cases."

Professor Ernst said when people are diagnosed with cancer they are often in shock and have a sense of crisis.

"Patients are overloaded with information and it is very difficult for them to assess the credibility of information they find on random websites."

Medical advice

Sir Paul Nurse, chief executive of Cancer Research UK, whose website was praised by the Exeter team, urged patients to seek medical advice before acting on complementary medicine advice.

"There is a confusing amount of information about cancer treatment and so-called 'alternative' cancer cures available on the internet.

"Many of these have no clinical or scientific basis and so it is vitally important that patients seek advice from their doctors before embarking on any alternative therapy."