Trials fail to show that herbal 'cures' have any success - instead, they could trigger reactions including blood clots, bleeding and nausea

Herbal remedies used to "cure" asthma are neither effective nor safe and are a "waste of money" in most cases, scientists said yesterday.

Herbal remedies used to "cure" asthma are neither effective nor safe and are a "waste of money" in most cases, scientists said yesterday.

None of the herbal treatments used by asthmatics has been proved to work and some could even trigger potentially dangerous reactions to other medicines, such as blood clots, bleeding and nausea, according to a study published in Thorax, a medical journal.

Medical experts said there was an "urgent need" for proper clinical trials into the effectiveness of alternative medicines for asthma to gauge their true role alongside conventional medicine, and urged people to be cautious because of the lack of regulation.

Figures produced by the National Asthma Campaign, an independent charity, show that alternative medicines have become more popular in recent years with nearly two-thirds of people with moderate asthma and nearly three-quarters with severe wheezing and breathlessness saying they used herbal remedies to treat the condition.

Researchers from Exeter University reviewed 17 clinical trials of a range of herbal asthma treatments including traditional Chinese medicines, such as concentrated Ginkgo leaf liquor, Indian medicines such as the herb Pichorrhiza kurroa, and marijuana.

Ginkgo Biloba is a popular "wonder" herb that is recommended for use for a range of treatments including dementia and asthma, and is considered to be one of the safest herbal medicines. But it was found to cause side-effects such as headaches, nausea, bleeding and seizures.

Alyson Huntley from the department of complementary medicines at the University of Exeter, who led the research, said that the health claims for the herbal medicines were based on poor-quality trials with little information about the people in the studies.

Only nine of the trials were "double blind" - where neither the participant nor the investigator knows whether the patient is being given the actual treatment or a control placebo. And 14 of the 17 trials reviewed scored three or less out of a maximum five on a scale designed to assess the quality of clinical studies.

"There is no evidence to support the claims of these herbal preparations," Dr Huntley said. "We don't really know the effects of them and there are quite a few safety issues and potentially harmful side-effects. People could be wasting their money because their efficacy is completely unproven.

"Although some trials showed some positive effect, the flaws in how they were done makes these claims invalid. We concluded that herbal medicinal products, even though in prevalent use, are of uncertain value in the treatment of asthma," she said.

Fiona Costello from the National Asthma Campaign urged caution in using herbal treatments. "We very much understand that people with asthma would ideally like an alternative to having to take regular medication to control their symptoms," she said.

"In general, complementary therapies, such as herbal medicines, have not been scientifically researched as extensively as conventional medicines. As an evidence-based charity we can only advise on complementary therapies that have been scientifically proven to be of benefit to people with asthma."

Asthma is one of the most common chronic diseases and its incidence is increasing at an alarming rate. The number of cases of the disease, which affects the small tubes that carry air in and out of the lungs, has risen by more than 50 per cent in developed countries in the past 25 years.

Scientists suspect that sterile modern lifestyles are contributing to the growth in the number of cases. There is no cure, but drugs can relieve many of the symptoms.

Dr John Harvey of the British Thoracic Society said that although some of the herbal treatments seemed to have benefits, none was totally free from side-effects or potential adverse reactions with other treatments.

"Research is vitally needed so that patients can be far clearer about the safety and benefits of different herbal remedies," he said.