[Placebo, placebo effect and clinical trials].

Recent studies have begun to unveil some of the biochemical bases of the placebo effect. Thus, while placebo analgesia is related to the release of endogenous opioids, placebo-induced dopamine release leads to motor improvement in Parkinson's disease. A theory proposes that the placebo effect is mediated by the activation of the reward circuitry. These biochemical findings indicate that the placebo effect is real, and suggest that many ethical arguments and controversies regarding the use of placebos should perhaps be reconsidered. While it may be advisable to minimize the placebo effect in clinical trials in order to estimate the pure effect of the active treatment, acting in the patient's best interest may require maximizing the placebo effect in the usual clinical setting.