From Der Spiegel:
For months now, a bitter battle has been taking shape in Great Britain between defenders of homeopathy, who are supported by no less than Prince Charles, and detractors who point to the lack of scientific evidence that the remedies offer anything more than a placebo effect. The royal family themselves have been adherents to homeopathy for generations and even Queen Elizabeth is given homeopathic remedies. After the war, her father King George VI even saw to it that Britain's National Health Service (NHS), the country's subsidized healthcare system, picked up the tab for homeopathic treatments.
Homeopathy is based on two fundamental ideas that skeptics like Singh can only shake their heads at. The first is the idea of the law of similars. The inventors of homeopathy believe that the cause of a symptom should also be treated with the cause. When treating someone, a homeopath considers which substance would cause the same symptoms in a healthy person. Arsenicum album, for example, which the activists in the campaign tried to overdose on, should in theory cause restlessness and nausea in a healthy person. But in an ill person, it is supposed to heal exactly these symptoms. If a patient has a fever, then a homeopath will look for a substance than can cause a fever in a healthy person.
The second principle is that of dilution: The more a medical ingredient is diluted and shaken, the stronger its effect will be — at least that's the assumption. But most homeopathic substances are so strongly diluted that molecules of the active ingredient can no longer be traced. Homeopaths still believe in the effects because they are convinced the water has a “memory.” Scientific proof for the claim is wanting.
More here.