When a doctor instructs a patient not to think of a monkey while taking a specific pill, we all know what would be on the patient’s mind when they pop that pill.
Similarly, when a doctor tells you that the side-effects of taking a particular pill are headache and nausea, it is likely that the patient suffers from headache and nausea even if the pill given were merely a placebo.
In an extreme case, when a 26-year-old man took 29 inert capsules believing them to be an antidepressant, he suffered from hypertension and needed to be rushed to a hospital. His symptoms only subsided after the true nature of the capsules were revealed to him.
The nocebo effect is one where we feel worse due to an intervention even if the intervention itself wasn’t administered. It is the opposite of the placebo effect, where we feel good as a result of a non-intervention. Both effects are also relevant outside of medical science – our expectations of any experience can actually influence its reality.
To a degree, we are rewarded with what we wish for. We are also cursed with whatever we fear.