Scientists suggest rationale for the placebo effect

Scientists may have discovered a possible cause of the mysterious placebo effect whereby a sham medical treatment results in a genuine benefit to the patient.

A study has found that production of a chemical "messenger" in the brain appears to play a critical role in generating the placebo effect in patients given fake treatments.

The findings could help to explain the many cases of "cures" resulting from nothing more than a belief by patients that they have been given a treatment that will help them to recover.

Doctors have treated many conditions using the placebo effect, from ridding people of warts by painting them with brightly coloured but inert dye to carrying out sham operations that have fooled patients into believing that they have had real surgery.

Placebo - which means "I shall please" in Latin - has long been accepted as a genuine phenomenon in medicine but no-one has been able to explain it satisfactorily, other than by saying it demonstrates the power of the mind over the body.

Clinical trials involving potent new drugs have to take account of the placebo effect by monitoring a control group of patients given a dummy pill made of sugar or starch, even thought scientifically the placebo effect cannot be explained.

However, Jon Stoessl, professor of neurology at Canada's University of British Columbia in Vancouver, believes that the placebo effect could be caused by the production of a powerful chemical in the brain called dopamine which is involved, among other things, 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 in certain parts of the brain.

Normally, when Parkinson's patients are given a chemical precursor to dopamine they show an improvement in levels of dopamine produced naturally in the brain, which makes them feel better.

However, when Professor Stoessl injected six of his Parkinson's patients with a simple saline solution he found that they, too, showed an improvement in levels of dopamine: he measured the average increase to be more than double.

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

"We were of course lucky that we were looking at a disease where dopamine plays a critical role," Dr Stoessl said.

"We think that the expectation of benefit is critical to the placebo effect no matter what is wrong.

And then once the expectation is there the brain may activate other machinery that may be more specific to the particular disease," he said.

Details of the experiment will be shown on BBC2's "Alternative Medicine: the evidence" on Tuesday night presented by Professor Kathy Sykes of Bristol University.

"Dopamine could be central to the placebo effect in all cases because of its connection to expectation," Professor Sykes said.

"We all release dopamine when we expect something good, whether it's food, sex, a drink or maybe a medical treatment.

And that means that the placebo mechanism that seems to work in Parkinson's may trigger the placebo effect in all of us," she said.

The BBC television programme follows patients who have undergone sham operations on their knee only to find that their symptoms improve as if they have had genuine surgery.

"What I'm most concerned about is that the placebo effect is much more powerful than we give it credit for," Professor Sykes said.

"We don't train our medical students to understand that if they give their patients the expectation that a treatment will work, it will help them to recover," she said.

- INDEPENDENT