Nocebo

A nocebo effect is said to occur when a patient's expectations for a treatment cause the treatment to have a worse effect than it otherwise would have.^[1][2] For example, when a patient anticipates a side effect of a medication, they can experience that effect even if the "medication" is actually an inert substance.^[1] The complementary concept, the placebo effect, is said to occur when expectations improve an outcome.

More generally, the nocebo effect is falling ill simply by consciously or subconsciously anticipating a harmful event. This definition includes anticipated events other than medical treatment. It has been applied to Havana Syndrome, where purported victims were anticipating attacks by foreign adversaries.^[3][4][5] This definition also applies to cases of electromagnetic hypersensitivity.

Both placebo and nocebo effects are presumably psychogenic but can induce measurable changes in the body.^[1] One article that reviewed 31 studies on nocebo effects reported a wide range of symptoms that could manifest as nocebo effects, including nausea, stomach pains, itching, bloating, depression, sleep problems, loss of appetite, sexual dysfunction, and severe hypotension.^[1]