Nocebo effect

The nocebo effect is the worsening of symptoms or emergence of adverse effects caused or amplified by negative expectations about a treatment or other exposure.

Expectancy effect: A change in experience or behavior caused partly by expectations about what will happen. Negative expectations are the defining psychological pathway through which nocebo effects arise.
Placebo effect: A beneficial change in symptoms or experience associated with treatment expectations and context rather than the treatment's specific active action. The placebo effect is the positive-expectation counterpart to nocebo effects.
Informed consent: A process ensuring that a person understands relevant information and voluntarily agrees to a medical intervention. Consent requires honest risk disclosure, which can be framed without unnecessarily amplifying fear.
War of the Ghosts experiment: A 1932 memory study by Frederic Bartlett showing how recall is reshaped by prior knowledge and cultural expectations. It illustrates how expectations can shape reports, a principle relevant to interpreting symptom experience.
Classical conditioning: A learning process in which a previously neutral cue comes to elicit a response after repeated pairing with another stimulus. Past experiences can make treatment cues trigger symptoms even without an active harmful ingredient.
Treatment expectancy: A person's belief about the likely effects of a treatment. Expectations about benefit or harm shape symptom experience and treatment response.
Risk communication: The exchange of information about hazards, their likelihood, and their consequences. Clear descriptions of probability and context can limit misleading impressions of treatment risk.
Chemotherapy anticipatory nausea: Nausea that occurs before chemotherapy, often after prior treatment experiences have conditioned the response. This clinical example demonstrates learned symptoms arising in anticipation of an adverse treatment.
Noxious stimulus: A stimulus capable of causing or signaling actual or potential tissue damage. The brain's pain systems can respond to anticipated threat as well as to noxious input.
Adverse event: An unfavorable medical occurrence during treatment, whether or not the treatment caused it. A reported side effect is not automatically caused by a nocebo process.

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