The Nocebo Effect
The Nocebo Effect is the inverse of the much more well known Placebo Effect. A nocebo is something that has no active ingredient but feels like it has a detrimental effect on someone. Derived from the Latin for "I shall harm" (Placebo means "I shall please") it was not coined until 1961 by Walter Kennedy, who stipulated that it should only refer to a strictly subject centered response, as seperate from genuine side-effects that may only manifest internally or as a result of behaviours arising from the psychological response. For example a patient may have an expectation an otherwise inert cream can cause itching, scratch the area affected and the resulting scratching can cause skin damage. The former is the nocebo response, the latter is not.
Both placebo and nocebo are similar in that they describe the human response to suggestion and expectation but also they are both a bucket we can put outliers or the noise we see in almost all clinical trials. In a trial of 50 people, a small number in the drug group may develop an unexpected, or even pre-suspected medical condition whilst on the trial but it does not always mean there is a causal link. It can be coincidence, poor controls, small samples or other common failures found in many trials.
But like placebo, human responses to stimuli are messy and inconsistent and often manifest in different ways. Conditions like Radio Frequency Hypersensitivity is often thought of as a nocebo response. Patients claim that they can somehow 'feel' radio waves, but when properly controlled and double-blind tested the condition goes away. Often people develop allergic reactions to things that they've read other people have and come to believe they are similarly affected. Usually self-diagnosed or by dodgy 'allergy clinics' who can, of course, provide you with the 'cure'. This is not to say anyone claiming to have an allergic reaction is somehow bogus or lying, many are very real and unless you're the individual's doctor then don't criticise. Often the patient's response is real to them even if it is psychological and that very fear and anxiety of expectation can cause an unwelcome physical manifestation.