Homeopathy: The Test - programme summary

Homeopathy was pioneered over 200 years ago. Practitioners and patients are convinced it has the power to heal. Today, some of the most famous and influential people in the world, including pop stars, politicians, footballers and even Prince Charles, all use homeopathic remedies. Yet according to traditional science, they are wasting their money.

"Unusual claims require unusually good proof"

The Challenge

Sceptic James Randi is so convinced that homeopathy will not work, that he has offered $1m to anyone who can provide convincing evidence of its effects. For the first time in the programme's history, Horizon conducts its own scientific experiment, to try and win his money. If they succeed, they will not only be $1m richer - they will also force scientists to rethink some of their fundamental beliefs.

Homeopathy and conventional science

The basic principle of homeopathy is that like cures like: that an ailment can be cured by small quantities of substances which produce the same symptoms. For example, it is believed that onions, which produce streaming, itchy eyes, can be used to relieve the symptoms of hay fever.

However, many of the ingredients of homeopathic cures are poisonous if taken in large enough quantities. So homeopaths dilute the substances they are using in water or alcohol. This is where scientists become sceptical - because homeopathic solutions are diluted so many times they are unlikely to contain any of the original ingredients at all.

Yet many of the people who take homeopathic medicines are convinced that they work. Has science missed something, or could there be a more conventional explanation?

The Placebo Effect

The placebo effect is a well-documented medical phenomenon. Often, a patient taking pills will feel better, regardless of what the pills contain, simply because they believe the pills will work. Doctors studying the placebo effect have noticed that large pills work better than small pills, and that coloured pills work better than white ones.

Could the beneficial effects of homeopathy be entirely due to the placebo effect? If so, then homeopathy ought not to work on babies or animals, who have no knowledge that they are taking a medicine. Yet many people are convinced that it does.

Can science prove that homeopathy works?

In 1988, Jacques Benveniste was studying how allergies affected the body. He focussed on a type of blood cell known as a basophil, which activates when it comes into contact with a substance you're allergic to.

As part of his research, Benveniste experimented with very dilute solutions. To his surprise, his research showed that even when the allergic substance was diluted down to homeopathic quantities, it could still trigger a reaction in the basophils. Was this the scientific proof that homeopathic medicines could have a measurable effect on the body?

The memory of water

In an attempt to explain his results, Benveniste suggested a startling new theory. He proposed that water had the power to 'remember' substances that had been dissolved in it. This startling new idea would force scientists to rethink many fundamental ideas about how liquids behave.

Unsurprisingly, the scientific community greeted this idea with scepticism. The then editor of Nature, Sir John Maddox, agreed to publish Benveniste's paper - but on one condition. Benveniste must open his laboratory to a team of independent referees, who would evaluate his techniques.

"Scientists are human beings. Like anyone else, they can fool themselves"

Enter James Randi

When Maddox named his team, he took everyone by surprise. Included on the team was a man who was not a professional scientist: magician and paranormal investigator James Randi.

Randi and the team watched Benveniste's team repeat the experiment. They went to extraordinary lengths to ensure that none of the scientists involved knew which samples were the homeopathic solutions, and which ones were the controls - even taping the sample codes to the ceiling for the duration of the experiment. This time, Benveniste's results were inconclusive, and the scientific community remained unconvinced by Benveniste's memory of water theory.

Homeopathy undergoes more tests

Since the Benveniste case, more scientists have claimed to see measurable effects of homeopathic medicines. In one of the most convincing tests to date, Dr. David Reilly conducted clinical trials on patients suffering from hay fever. Using hundreds of patients, Reilly was able to show a noticeable improvement in patients taking a homeopathic remedy over those in the control group. Tests on different allergies produced similar results. Yet the scientific community called these results into question because they could not explain how the homeopathic medicines could have worked.

Then Professor Madeleine Ennis attended a conference in which a French researcher claimed to be able to show that water had a memory. Ennis was unimpressed - so the researcher challenged her to try the experiment for herself. When she did so, she was astonished to find that her results agreed.

Horizon takes up the challenge

Although many researchers now offered proof that the effects of homeopathy can be measured, none have yet applied for James Randi's million dollar prize. For the first time in the programme's history, Horizon decided to conduct their own scientific experiment.

The programme gathered a team of scientists from among the most respected institutes in the country. The Vice-President of the Royal Society, Professor John Enderby oversaw the experiment, and James Randi flew in from the United States to watch.

As with Benveniste's original experiment, Randi insisted that strict precautions be taken to ensure that none of the experimenters knew whether they were dealing with homeopathic solutions, or with pure water Two independent scientists performed tests to see whether their samples produced a biological effect. Only when the experiment was over was it revealed which samples were real.

To Randi's relief, the experiment was a total failure. The scientists were no better at deciding which samples were homeopathic than pure chance would have been.

Read more questions and answers about homeopathy.