[Nocebo placebo, the hidden side of our treatments].

NOCEBO PLACEBO, THE HIDDEN SIDE OF OUR TREATMENTS. Our knowledge of the placebo effect and its opposite, the nocebo effect, has changed dramatically in the last 20 years. Any treatment activity induces this type of effect. The placebo groups in clinical studies have biases that profoundly alter their neutrality. The nocebo effect is omnipresent in daily practice, it contributes to induce many of the adverse drug effects. The use of «impure» placebos is also widespread in daily practice. The placebo effect has an objectivable and reproducible neurobiological substrate. Its therapeutic effects are well documented. Disorders, symptoms involving the central nervous system (CNS) respond more easily to placebo. These new data make it possible to improve clinical practices by developing the quality of relationships with patients and families as well as the methodology of clinical trials.