Homeopathy is not a coherent system but a loose collection of ideas, each of which is scientifically unsupported. The most important are the following two:
The similia principle
Homeopaths sometimes call this the ‘Law of Similars’. The inventor of homeopathy, Samuel Hahnemann, may have believed that he’d discovered a natural law when he tested a widely-used malaria treatment — chinchona bark — on his own healthy person and decided that the symptoms he suffered as consequence were similar to those of malaria itself. But ideas of similarity are highly subjective and homeopaths sometimes disagree amongst themselves about which remedy is the true ‘similimum’ for the ailment in question. There is no scientific support for the notion that ‘like treats like’ as a general principle. Experiments conducted by Hahnemann for the purpose of establishing which substances produce which symptoms are scientifically worthless, not least because he used volunteers who knew what they were taking and what effects were anticipated and who also knew each other and could compare notes. Nor did Hahnemann use any kind of control group.
Less is more
The most controversial aspect of homeopathy is the idea that the smaller the dose, the more potent it becomes. It is sometimes called the ‘Law of Infinitesimals’ but this is mere invention — there is no such law. Homeopathic remedies are typically diluted beyond Avogadro’s number, which means they contain not a single molecule of the original ingredient. Hahnemann routinely recommended a dilution of 30c, which is 1 part ingredient to 1,000,000,000, 000,000,000,000,000,000,000, 000,000,000,000,000,000,000,000,000,000 parts dilutant. Homeopaths get round the problem of the disappearing ingredient by hypothesising that the memory of the original ingredient is somehow imprinted onto the water it is diluted in, through the process of ‘sucussion’. The question of how the dilutant remembers only the required ingredient and forgets everything else that has ever been in it has been addressed by the suggestion that using doubly-distilled and de-ionised water as the dilutant, eliminates the problem. As there is no scientific evidence to support the notion that water has the capacity to remember and selectively reproduce the effects of matter that it no longer contains, it follows that there is no evidence to support the notion that distilling and de-ionising the water will cleanse it of this memory.
Hundreds of clinical trials of homeopathy have been carried out in many different countries. Those that suggest a positive effect tend to be small and of poorer quality than those that don’t. The totality of evidence available demonstrates conclusively that homeopathy, as a treatment, works no better than placebo in placebo-responsive conditions. Homeopaths commonly claim that four out of five meta-analyses of homeopathy have been ‘positive'; the British Homeopathic Association made this claim in their submission to the House of Commons Science and Technology Committee inquiry. However, an examination of the papers in question reveals this claim to be mendacious.
1. Kleijnen et al, 1991, meta-analysis, 107 trials.
CONCLUSIONS: At the moment the evidence of clinical trials is positive but not sufficient to draw definitive conclusions because most trials are of low methodological quality and because of the unknown role of publication bias. This indicates that there is a legitimate case for further evaluation of homoeopathy, but only by means of well performed trials.
2. Boissel et al, 1996, critical literature review commissioned by the European Commission Homeopathic Medicine Research Group, 184 trials. Boissel controversially combined p-values of the highest quality trials to arrive at this conclusion:
From the available evidence it is likely that among the tested homoeopathic approaches some had an added effect over nothing or placebo….but the strength of this evidence is low because of the low methodological quality of the trials.
3. Cucherat et al 2000, used the same data as Boissel but with the addition of at least two more trials. Boissel was one of the four-strong research team and authored the report, which concluded:
There is some evidence that homeopathic treatments are more effective than placebo; however, the strength of this evidence is low because of the low methodological quality of the trials. Studies of high methodological quality were more likely to be negative than the lower quality studies. Further high quality studies are needed to confirm these results.
Early in 2010, science writer Martin Robbins wrote:
I spoke to Jean-Pierre Boissel, an author on two of the four papers cited (Boissel et al and Cucherat et al), who was surprised at the way his work had been interpreted.
“My review did not reach the conclusion ‘that homeopathy differs from placebo’,” he said, pointing out that what he and his colleagues actually found was evidence of considerable bias in results, with higher quality trials producing results less favourable to homeopathy.
Source: Guardian online
4. Linde 1997, meta-analysis, 89 trials.
The results of our meta-analysis are not compatible with the hypothesis that the clinical effects of homeopathy are completely due to placebo. However, we found insufficient evidence from these studies that homeopathy is clearly efficacious for any single clinical condition. Further research on homeopathy is warranted provided it is rigorous and systematic.
Linde produced a follow-up paper in 1999, which concluded:
The evidence of bias [in homeopathic trials] weakens the findings of our original meta-analysis. Since we completed our literature search in 1995, a considerable number of new homeopathy trials have been published. The fact that a number of the new high-quality trials… have negative results, and a recent update of our review for the most “original” subtype of homeopathy (classical or individualized homeopathy), seem to confirm the finding that more rigorous trials have less-promising results. It seems, therefore, likely that our meta-analysis at least overestimated the effects of homeopathic treatments.
Linde co-authored a brief article in the Lancet in December 2005. In it he wrote,
We agree (with Shang et al) that homoeopathy is highly implausible and that the evidence from placebo-controlled trials is not robust…Our 1997 meta-analysis has unfortunately been misused by homoeopaths as evidence that their therapy is proven.
Source: The Lancet
5. Shang et al, meta-analysis 2005, 8 homeopathy trials selected from 110 and 6 trials of conventional medicine selected from 110.
Biases are present in placebo-controlled trials of both homoeopathy and conventional medicine. When account was taken for these biases in the analysis, there was weak evidence for a specific effect of homoeopathic remedies, but strong evidence for specific effects of conventional interventions. This finding is compatible with the notion that the clinical effects of homoeopathy are placebo effects.
The Science and Technology Committee published its report in February 2010. It concluded that
To maintain patient trust, choice and safety, the Government should not endorse the use of placebo treatments, including homeopathy. Homeopathy should not be funded on the NHS and the MHRA should stop licensing homeopathic products.