Nocebo effect

The nocebo effect is the phenomenon whereby a patient who believes that a treatment will cause harm actually experiences adverse effects. Nocebo translates from Latin as "I shall harm". More broadly, the effectiveness of, for instance, Voodoo curses on suggestible victims can be considered an example of the effect.

The nocebo effect is distinguished from older concepts such as sociogenic illness and psychosomatic illness, which are broader terms where a known or unknown cause with cultural or psychological factors is involved. Distinguishing between these effects can be a difficult problem for medical semiotics, or the study of how to interpret the patient's description of their ailments.

The nocebo effect is the reverse of the well-known placebo effect.