Benedetti, 53, first became interested in placebos in the mid-'90s, while researching pain. He was surprised that some of the test subjects in his placebo groups seemed to suffer less than those on active drugs. But scientific interest in this phenomenon, and the money to research it, were hard to come by. "The placebo effect was considered little more than a nuisance," he recalls. "Drug companies, physicians, and clinicians were not interested in understanding its mechanisms. They were concerned only with figuring out whether their drugs worked better."

Part of the problem was that response to placebo was considered a psychological trait related to neurosis and gullibility rather than a physiological phenomenon that could be scrutinized in the lab and manipulated for therapeutic benefit. But then Benedetti came across a study, done years earlier, that suggested the placebo effect had a neurological foundation.

US scientists had found that a drug called naloxone blocks the pain-relieving power of placebo treatments. The brain produces its own analgesic compounds called opioids, released under conditions of stress, and naloxone blocks the action of these natural painkillers and their synthetic analogs. The study gave Benedetti the lead he needed to pursue his own research while running small clinical trials for drug companies.

Now, after 15 years of experimentation, he has succeeded in mapping many of the biochemical reactions responsible for the placebo effect, uncovering a broad repertoire of self-healing responses. Placebo-activated opioids, for example, not only relieve pain; they also modulate heart rate and respiration. The neurotransmitter dopamine, when released by placebo treatment, helps improve motor function in Parkinson's patients. Mechanisms like these can elevate mood, sharpen cognitive ability, alleviate digestive disorders, relieve insomnia, and limit the secretion of stress-related hormones like insulin and cortisol.

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