In the 18th century, Samuel Hahnemann, the inventor of homeopathy, came up with the following ideas:

• The more dilute a homeopathic solution is, the more effective it is.
• Like 'cures' like.

Many homeopathic products are so dilute that the doses administered are highly unlikely to contain even a single molecule of the original substance from which they were made. Thus any benefit from these 'remedies' is due almost certainly to the placebo effect and this is backed up by the evidence.

To achieve such absurdly dilute solutions, homeopaths use a technique called serial dilution.

What on earth is serial dilution?

One drop of the original substance to be diluted is added to 99 drops of water (or ethanol) and the solution is shaken vigorously. Homeopaths believe this transfers the 'healing powers' of the original substance to the water. They call this 'succussion'. The resulting solution is called a 1C dilution. One drop of this solution contains, on average, 100 times fewer molecules of the substance than the original drop. Other dilutions (eg 1 drop to 9 drops of water to give a 1X dilution) are also used, but the procedure remains the same.

If one drop of this 1C dilution is added to another 99 drops of water, a 2C dilution is made. One drop of this 2C solution contains, on average, 10,000 times fewer molecules than the original drop. Many homeopathic products are diluted to 6C, 30C or even higher. To stand a good chance of swallowing just one molecule of the original substance one would need to drink about:

• 20 Olympic swimming pools of a 16C dilution
• 2,000,000,000 Olympic swimming pools of a 20C dilution.

For a 30C dilution, one would need to swallow a volume greater than all the water present in all the oceans of our entire planet in order to stand a good chance of swallowing just one molecule of the original substance! Even if the original substance was active, there is absolutely nothing left after all these dilutions.

A drop of the final dilution is usually then dropped on to small sucrose/lactose 'pills' or 'pillules', somehow passing on its 'healing powers' to the sugar.

Faced with these indisputable scientific facts and unable to accept the power of the placebo effect, homeopaths have suggested that water might have a memory and remember what had originally been dissolved in it. However, there are no plausible explanations why water should have a memory of any substance it has been in contact with, never mind just the one substance the homeopath wants it to remember for its 'healing' power.

Like cures like?

How like may cure like has not been explained. Some homeopaths say it works like a vaccine. However, this is not true since vaccines work by priming the immune system to recognise a particular disease with a safe version of the pathogen (an altered virus, for example). Homeopaths claim that only the symptoms of the disease and treatment need match, no matter what condition or pathogen lies behind them. This does not fit with how the body works and is problematic; eg a headache could be a symptom of stress or a brain tumour and the required medical treatments are very different.

The substances diluted by manufacturers of homeopathic products are very varied, including plant extracts and minerals, but some are made from man-made substances like prescription medicines and other man-made chemicals. Because of this and because of the extremely artificial diluting and succussion, homeopathic products are anything but natural!

The evidence

There is no credible evidence that homeopathic products work any better than, well, sugar pills. Over 150 clinical trials have failed to show that homeopathy works. Some small-scale studies have yielded positive results, but this is due to poor methodologies or random effects. When all the evidence from many trials is pooled together, homeopathy is no better than a placebo.

A recent Lancet paper compared 110 homeopathy trials with 110 conventional medicine trials. The authors found that the higher quality trials offered strong evidence that conventional medicines work and no evidence that homeopathic products work. In other words, the better the research, the less effective homeopathy appears. Over a dozen similar analyses have arrived at the same conclusion: that homeopathy does not perform anybetter than placebos.

All-in-all, there is no good reason why homeopathic products should be called medicines and no good reason why they should be sold in pharmacies alongside medicines that have had to pass stringent tests for efficacy.