Homeopathy, a form of complementary medicine that is available on the NHS, is dealt a double blow today with the publication of two studies that conclude it has very little proven effect on patients.

Homeopathy has co-existed with conventional medicine in the NHS since the health service began. There are five homeopathic hospitals and the two largest, in Glasgow and London, have in-patient units.

Many GPs either practise homeopathy themselves or will refer patients to a homeopath on request. Around 470,000 people take homeopathic remedies every year.

Yet the NHS Centre for Reviews and Dissemination, based at York University, has produced a comprehensive review of the clinical trials that have been carried out to assess what benefit patients receive from homeopathy.

It concludes: "There is currently insufficient evidence of effectiveness to recommend homeopathy as a treatment for any condition, or warrant significant changes in current provision of homeopathy."

The principle of homeopathy is that "like should be cured with like". But sceptics argue, says the York paper, "that homeopathy cannot work because of the use of remedies that are diluted to such a degree that not even a single molecule of the starting substance remains".

A further salvo appears in the British Medical Journal, which reports on a study to assess the impact of homeopathic treatment on people with asthma.

Scientists from Southampton and Plymouth enrolled 242 people and randomly assigned them to homeopathic treatment or placebo.

They found that patients given homeopathic remedies did no better than those on dummy medicines.