The Flip Side of Placebos: The Nocebo Effect

Studies find that the confounding beneficial effect of placebos has an equally mysterious flip side: the nocebo effect

Corbis

If any pill has been shown undeniably to work in clinical trials, it is the sugar pill, along with its close cousin, the sham treatment. The placebo, as such inert and cost-free remedies are known, can relieve depression as effectively as Prozac, ease discomfort as effectively as acupuncture, and reduce as much disability and back pain as a widely used vertebral surgery that costs up to $5,000.

That the effect of bogus treatments is real has long been known, but the mechanism behind them is still largely a scientific mystery. The standard explanation is that we are just...