Samuel Hahnemann, the German doctor who developed homeopathy, was born 250 years ago this week. Troubled by the uselessness and often harmfulness of the medical treatments of his time, he tried to find a therapy that was effective and devoid of risks. His new medical system was based on two overriding concepts: the "like cures like" and "less is more" principles.
The "like cures like" principle says that, if healthy people experience a symptom (say, a headache) after taking a drug, this medicine can be used to treat headache sufferers. The "less is more" principle postulates that the process of homeopathically diluting a drug makes it stronger, not weaker. When the remedy is so dilute that not a single molecule is left, it is particularly potent. The water will have developed a "memory" of what it was once in contact with.
Homeopaths regard these principles as general laws of nature. To others, they fly in the face of science. If the rules of homeopathy are correct, we would need to rewrite major sections of our physics and chemistry textbooks. "Where there is no molecule, there will be no action," my pharmacology teacher would say. But homeopaths counter that homeopathy does not rely on pharmacology but on "energy". The trouble is, no one has ever proved the existence of such "energy" or explained how it could help.
But for all its implausibility, say homeopaths, what counts is that it helps patients. And patients do get better, particularly those suffering from chronic conditions such as allergies, headache or eczema. A Norwegian study with more than 1,000 patients recently showed that seven out of 10 experienced "meaningful improvement".
Homeopathy is one of the most popular complementary medicines. In the UK, we have around 3,000 registered homeopaths. They are either doctors who have received specialised training, or lay homeopaths - they prefer "professional homeopaths" - who have not been to medical school. The proportion of GP practices offering provision of or referral to homeopathy has increased from 17% in 1995 to 21% in 2001. Currently, 70% of all practices refer patients to homeopaths.
If we agree that homeopathy is popular and that many patients benefit from it, why insist on hard evidence? Because scientists claim that patients perceive benefit purely because homeopaths are gentle, intuitive physicians equipped with time, empathy and sympathy. They say it is not the medicine that does the trick, but the power of placebo and the therapeutic encounter. Unsurprisingly, few homeopaths agree.
Looking for hard evidence, German researchers assembled all the relevant trials, did some clever statistics with them, and concluded (in the Lancet) that "the clinical effects of homeopathy are not completely due to placebo". The scientific storm could not have been greater. Sceptics outdid each other in finding flaws in the Lancet paper. And, of course, there were flaws. So the German group looked at their data again, applied even cleverer statistics, and published a reanalysis. This time, the conclusions were more cautious: "There was clear evidence that studies with better methodological quality tended to yield less positive results." In other words, it could have been a fluke.
So the argument rages on. In the mid-19th century, John Forbes, physician to Queen Victoria, stated that homeopathy bears "resemblance to what we have heard or seen of magical ceremonies and the tricks of conjurors". The entry for homeopathy in the Encyclopaedia Britannica of 1891 reads: "Hahnemann's errors were great." And less than half a year ago, the Académie de Medicine of France said that homeopathy is "based on prejudices devoid of any foundation".
I was trained in homeopathy many years ago. Occasionally I used it on patients and now I am researching it scientifically. Homeopathy, I admit, fascinates me. On the one hand, homeopathy cannot possibly work. On the other hand, there is evidence suggesting that it does. Wouldn't it be nice to know the truth?
· Edzard Ernst is professor of complementary medicine at the Peninsula medicine school at the universities of Exeter and Plymouth.