A nocebo is something that induces a feeling of ill-health for no very good medical reason, the opposite of a placebo. (The latter is the medical term for a medication or other treatment which is given to a patient for the psychological benefit it will bring rather than for any likely therapeutic effect. The word is also used to describe dummy drugs given to some patients in clinical trials, because medical researchers have to take into account the positive effect on patients of giving them a medication of any kind, even if it isn’t effective. In Latin placebo means literally “I shall be acceptable or pleasing”, from the verb placere, to please. It came into medical terminology from liturgical Latin near the end of the eighteenth century.) Nocebo, on the other hand, is a very modern word; it’s recorded only from the 1990s and until recently you wouldn’t have come across it outside specialist research publications. It’s obviously modelled on placebo, but it comes instead from nocere, to harm, and so has a literal meaning of “I shall cause harm or be harmful”. The word has come into being because researchers have become aware they also have to take into account factors that might have a negative effect on treatments. These aren’t usually medications but influences such as beliefs, attitudes and cultural factors.
Research has also shown that the nocebo effect can reverse the body’s response to true medical treatment from positive to negative.
Robert S and Michèle R Root-Bernstein, Honey,
Mud, Maggots and Other Medical Marvels (1997)
He stresses that while most everyone is familiar with the placebo effect, few are aware of the nocebo effect — the ability of negative beliefs and expectations to actually cause harm.
Skeptical Inquirer (Committee for the Scientific Investigation
of Claims of the Paranormal), Sept. 1997