Scientists discover chemical link that may explain the 'placebo effect'

Scientists may have discovered a possible cause of the "placebo effect", where a sham medical treatment results in a genuine benefit to the patient. A study has found production of a chemical "messenger" in the brain appears to play a critical role.

Jon Stoessl, professor of neurology at the University of British Columbia in Vancouver, believes the placebo effect could be caused by the production of a chemical in the brain called dopamine, which is involved in triggering the expectation of pleasure and reward.

Professor Stoessl carried out a study on patients suffering from Parkinson's disease, which is known to result from a lowering of normal levels of dopamine.

Normally when Parkinson's patients are given a chemical precursor to dopamine they show an improvement in levels of dopamine produced naturally, which makes them feel better. But when Professor Stoessl injected six of his patients with a simple saline solution he found that they too showed an improvement in levels of dopamine - the average increase was more than double.

The patients given the saline solution were told they were to be given the actual treatment and as a result they were expecting to feel an improvement, Professor Stoessl said.

Details will be shown in Alternative Medicine: the evidence at 9pm on BBC2 tomorrow.