When critics point out to politicians or regulators that homeopathy is not backed by any good evidence and is just a placebo, one response is "What's the harm?". In other words, if the placebo effect is positive and the side effects are zero, then what's wrong if people want to waste a bit of money on sugar pills? But is homeopathy really safe?
Unfortunately, homeopathy can have surprising and dangerous side-effects. These have nothing to do directly with any particular homeopathic remedy, but rather they are an indirect result of what happens when homeopaths replace doctors as sources of medical advice.
For example, many homeopaths have a negative attitude towards immunization, so parents who are in regular contact with a homeopath may be less likely to immunize their child. To evaluate the extent of this problem, Edzard Ernst and Katja Schmidt at Exeter University conducted a revealing survey among UK homeopaths. Having obtained e-mail addresses from online directories, they sent an e-mail to 168 homeopaths in which they effectively pretended to be a mother asking for advice about whether or not to vaccinate her one-year-old child against measles, mumps and rubella (MMR). This was in 2002 when the controversy over MMR was subsiding and the scientific evidence was clearly in favour of vaccination. Of the 77 respondents, only two advised the mother to immunize, so it is clear that the overwhelming majority of homeopaths will not encourage immunization.
Perhaps the greatest danger occurs when homeopathy replaces a conventional treatment. I first encountered this problem in 2006 when I tried to find out what homeopaths would offer to a young traveller seeking protection against malaria. Working with Alice Tuff and the charity Sense About Science, we developed a storyline in which Tuff would be making a ten week overland trip through West Africa, where there is a high prevalence of the most dangerous strain of malaria, which can result in death within three days. Tuff, a young graduate, would explain to homeopaths that she had previously suffered side-effects from conventional malaria tablets and wondered if there was a homeopathic alternative.
Before approaching homeopaths, however, Tuff visited a conventional travel clinic with exactly the same storyline, which resulted in a lengthy consultation. The health expert explained that side-effects were not unusual for malaria tablets, but that there was a range of options, so a different type of tablet might be advisable. At the same time, the health expert asked detailed questions about Tuff's medical history and offered extensive advice, such as how to prevent insect bites.
Next Tuff found a variety of homeopaths by searching on the internet, just as any young student might do. She then visited or phoned ten of them, mainly based in and around London. In each case, Tuff secretly recorded the conversations in order to document the consultation. The results were shocking. Seven out of the ten homeopaths failed to ask about the patient's medical background and also failed to offer any general advice about bite prevention. Worse still, ten out of ten homeopaths were willing to advise homeopathic protection against malaria instead of conventional treatment, which would have put our pretend traveller's life at risk.
The homeopaths offered anecdotes to show that homeopathy is effective. According to one practitioner, 'Once somebody told me she went to Africa to work and she said the people who took malaria tablets got malaria, although it was probably a different subversive type not the full blown, but the people who took homeopathics didn't. They didn't get ill at all.' She also advised that homeopathy could protect against yellow fever, dysentery and typhoid. Another homeopath tried to explain the mechanism behind the remedies: 'The remedies should lower your susceptibility; because what they do is they make it so your energy – your living energy – doesn't have a kind of malaria-shaped hole in it. The malarial mosquitoes won't come along and fill that in. The remedies sort it out.'
The investigation took place in the run-up to the summer holiday season, so this became part of a campaign to warn travellers against the very real dangers of relying on homeopathy to protect against tropical diseases. One case reported in the British Medical Journal described how a woman had relied on homeopathy during a trip to Togo in West Africa, which resulted in a serious bout of malaria. This meant she had to endure two months of intensive care for multiple organ system failure. In this case, the placebo effect offered no protection.
That's the harm.Simon Singh is a supporter of the 10:23 campaign. He is the author of books such as "Fermat's Last Theorem" and backs the campaign for libel reform (www.libelreform.org/sign).