Physiologic Basis for Placebo Effect

A new study shows that the placebo effect is not all psychological. ScienceNow reports:

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New research indicates that when people expect a treatment to numb their hurt, their brains release endorphins, the body's own opioid painkillers. Experts say the findings are the first to nail down the molecular basis of the placebo effect.

Scientists have long suspected that placebos tap into opioid circuitry within the brain. Chemical blockades of these circuits abolish the placebo effect, and placebos increase blood flow to areas of the brain rich in opioid receptors. To obtain direct evidence that opioid receptors mediate the placebo response, neuroscientist Jon-Kar Zubieta of the University of Michigan in Ann Arbor and colleagues used a radioactive tracer molecule that sticks to vacant opioid receptors.

First, the team induced a painful, sustained ache in 14 men by injecting a salt solution into their jaw muscles. The researchers then scanned the subjects' brains using positron emission tomography, which locates the radioactive tracer. During one scan, the researchers offered no relief from the pain. During another, they told the subjects they were administering an experimental drug thought to ease pain, but instead gave only saline. When subjects got the placebo, they experienced a decreased sensitivity to pain, and their brain scans revealed occupied opiate receptors, an indication that opioids had bound to them. "This is not just a psychological phenomenon," says Zubieta, whose team reports its findings 24 August in the Journal of Neuroscience. "It is a real chemical mechanism."

This may not explain all placebo effects, but it is interesting.

The news article provides this link at the FDA for further reading.