But there's another side to the power of suggestion: Patients may develop symptoms and side effects purely because they've been told about them.

A new report analyzes the so-called "nocebo effect" and suggests that doctors learn how to better "exploit the power of words" for the benefit of patients. Patients themselves are crucial players, too, said study lead author Dr. Winfried Hauser, an associate professor of psychosomatic medicine at the Klinikum Saarbrucken in Germany.

"It is not only the power of the mostly unintentionally negative words of physicians and nurses, but also the power of negative expectations, negative experiences and fears of the patients," Hauser said.

The report, which recently appeared in the journal Deutsches Arzteblatt International, examines existing research about the nocebo effect and finds that scientists and doctors have spent very little time trying to understand it. About 2,200 studies have examined the placebo effect, but only a few dozen explored the nocebo effect.