[Placebo: an unappreciated factor in medicine]

Placebo is a provoking factor in medicine that is discussed controversially and not fully understood so far. From the scientific point of view and according to evidence-based medicine a proved indication to prescribe a placebo does not exist. Therapy of pain may be an exclusion. In our daily work we consciously use the placebo-effect, but on the other hand we are committed to the placebo-phenomenon. This article gives an overview of various aspects of placebo. The currently supported theory about the placebo response, conditioning and expectancy, are discussed. Further, the side effects (nocebo-phenomenon) and the utility of placebo in randomised clinical trials is highlighted.