Placebo and nocebo effects, medication bias, and hearsay

The placebo effect is well known to physicians and probably accounts for observed patient response to therapy more often than most of us are willing to admit. In randomized clinical trials, patients in the placebo group invariably improve more than individuals outside of the trial who are treated with standard therapies.1,2 The nocebo effect, less well known, consists of undesirable responses to therapy resulting from negative patient expectation. Thus, if a physician emphasizes possible adverse events when discussing an impending therapeutic intervention, it is more likely that the patient will experience them.