The belief that a medicine will work triggers the release of natural painkillers in the brain, scientists have discovered – helping to explain the so-called placebo effect.

According to research, when patients expect a treatment to be effective the part of the brain that is responsible for pain control is activated, causing the release of endorphins. The result is that the patients feel better, whether or not the treatment had any direct effect.

The finding helps to explain why some people claim to benefit from remedies that do not contain any active pain-relief ingredients. It also strengthens the argument that many established medical treatments derive part of their effectiveness from the placebo effect.

For instance, scientists have ascribed about 75 per cent of the benefit of antidepressants to the patients’ expectation that the drugs will make them better. Many GPs observe that patients appear to show improvements only days after being prescribed antidepressants, while the direct effects take longer to kick in.

In the study, reported at the International Symposium for Magnetic Resonance in Medicine in Berlin, the brains of 19 healthy volunteers were scanned using functional magnetic resonance imaging. During the scan, they received laser “pinpricks” to their hands. The volunteers were told that a pain-relief cream had been applied to one of their hands and a control cream to the other. But an identical control cream was administered to both hands. When people believed that they had received the active cream, they reported feeling less pain and showed less activity in brain areas associated with feeling pain.

The mechanism by which the placebo effect alleviated pain has remained unknown. The study suggests that a part of the brain associated with pain control, known as the rostral anterior cingulate cortex or rACC, is responsible.

“When participants thought they had been given effective pain relief, the rACC showed significantly more activity,” said Professor Christian Büchel, who led research at the University of Hamburg. “This region is known to be very rich in opiate receptors and signalling the release of opiates.”

The implication is that the placebo effect is grounded in physiology. “We’ve shown that the placebo effect works in a very similar way to opiate drugs such as morphine or codeine,” Professor Büchel said. The findings will reignite debate over the prescription of “sugar pill” cures. In a study in 2005, 48 per cent of Danish GPs admitted to having prescribed a placebo at least ten times in a year.

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