The word placebo derives from the Latin word „placere“ and means “I shall please”. A placebo is a sham or simulated medical intervention. I can be a substance which simulates the original drug (“verum”), but does not contain its specific agent. The placebo is taken by persons, who assume that they have taken a “real” drug. The psychobiological changes, which can be observed in persons taking a placebo, are called the placebo effect. Inert tablets are often used as placebos. The patient is given an inert pill, told that it may improve his/her condition, but not told that it is in fact inert. Consequently the placebo has no direct influence on the biochemical processes of a disease. Nevertheless many of these patients experience an improvement of their symptoms. It is presumed that unspecific psychological factors like the patients expectation or conditioning cause this so called placebo effect. The negative effect of a sham or simulated medical intervention, which can generate or impair symptoms as well as prevent an improvement, is called the nocebo effect. A sham treatment, which has no positive effect on the patient’s condition accordingly called nocebo.