What is nocebo?

Nocebo, which means, “I will harm” in Latin, is a term that describes the negative reaction of a subject in a medical trial after being given an inert substance or placebo.  This is a reaction that is not generated as a result of the chemical of a drug but rather a reaction that is generated as a result of a subject’s belief and/or expectations that the medication will cause problems.

The term "placebo" comes from the Latin for "I will please." Its opposite is a nocebo, from the Latin for "I will harm." The nocebo effect is a side effect from an apparently inert substance or a sham treatment. Healthy individuals have adverse effects from a placebo about 25 percent of the time, and if patients are specifically asked about adverse effects, the proportion can rise to 70 percent. Nocebo response" usually describes an adverse reaction to a placebo, but the term could also be applied to an unusual or exaggerated adverse response to a medication. Does that mean that a nocebo effect is not real? Not at all; it is just as real as the real thing.