What are we going to do about the scam of homeopathy? As Richard Dawkins proclaimed, in the second of his "Enemies of Reason" series, all the evidence shows that homeopathic remedies are nothing but water and, as you'd expect of a drink of water, the only effect they have is a placebo. But it was much less fun to see Dawkins tackling this topic than it was to see him take on astrology, spirit guidance and crystal balls the previous week. The reason, I think, is not just that serious health issues are involved, but that the millions of people who buy homoeopathic remedies really do feel better for them. It might help to tell people how crazy it is to believe in newspaper astrologers or crystals, but it won't help telling them that homeopathy doesn't really do what it claims, or that it's entirely based on a discredited 18th century system, when they actually do get better.

Dawkins revealed three reasons why they get better. First, alternative therapists often spend an hour with their patients, getting to know them, discussing their problems, and generally taking an interest in their lives and troubles; by contrast NHS GPs can only spend on average eight minutes with each patient. Second, alternative therapists often touch, stroke and caress their patients, with the explanation that they are aligning the chakras, releasing the energies, or feeling the blockages. Their explanations are false but touch itself can have a wonderfully soothing and relaxing effect that promotes healing. GPs, bound by having to tell the truth and by rules of propriety, cannot use such lies and cannot stroke and soothe their patients even if they wish to.

Third, there is the whopping great placebo effect, induced by the way remedies are marketed, and by the power of the therapist to convince patients of the effects. Here is the worst problem for real doctors. Effective medicine has always depended on placebo effects and self-healing, but using the placebo effect means effectively lying, and modern medicine has no place for systematic lying. Quite rightly, GPs are trained to tell the truth about a medicine's effectiveness, explaining the likely outcomes, the side effects, and the plusses and minuses. For many self-limiting or stress-induced illnesses the best treatment may easily be a chalk pill along with a convincing statement that it will work wonders given by someone you trust - but GPs cannot use this wonder non-drug. Alternative therapists don't have to do tell the truth. They can tell whatever lies they like about hidden lines of force, invisible energies, and healing colours, and so they have appropriated the powers of the placebo effect to themselves.

But Dawkins missed a trick here. Money. Placebo effects increase not only with the convincingness of the explanation and the perceived power of the therapist, but with their cost. It's cognitive dissonance. If you get something for free you value it less than if you have to pay a lot for it. In a country with a national health service, with most treatments free, doctors can't use that effect either, but the alternative therapists do. People who buy their own treatments are likely to find they get better quicker than those who get them for free.

So what to do? TV programmes exposing the fraud will have little effect, and we can't ban people from selling little bottles of water. We can do our best to prevent homeopathy being given on the NHS, but there are many convinced believers who will fight hard to keep it.

So here's a thought. How about putting a heavy tax on homoeopathic remedies? With the millions sold each year even a few pounds a bottle would raise plenty of funds. The placebo effect would be strengthened, and the money raised could be used to provide what really matters - time that the doctor can spend with her patients.

I'm sure this is not a magic pill either, but we have to do something to bring back the power of time, kindness, and the placebo effect into real medicine instead of leaving it to the alternatives.