Nocebo
（重定向自Nocebo Effect）
In medical and psychological research a nocebo is an inert substance or treatment that appears to cause an adverse effect on a patient or participant although it has no known biological effect. This adverse effect has been called a nocebo effect. The term derives from placebo, which is a a treatment used as a control condition, usually paired with one or more treatments that are being tested for their effects. Placebos sometimes induce a beneficial effect, such as a relief from pain, and such an effect is called a "placebo effect." One speaks of the nocebo effect if the control treatment induces an adverse effect (for example, the participant or patient feels ill). This nocebo effect is relatively uncommon and poorly understood.