[Placebo effects and controlled clinical trials].

Placebo effects have been recognized for a long time, but the underlying mechanisms are unknown. The analgesic effect of placebo has been studied, and one hypothesis is that placebo-induced analgesia is mediated by endorphins. The opiate antagonist naloxone has been used in an attempt to prevent this analgesia. Partial antagonism has been shown, but the placebo still has a considerable analgesic effect. This means that release of endorphins cannot be the only explanation of the analgesia. Patients participating in clinical trials to compare an active drug with a placebo are informed that they may receive the latter. This information leads to a reduction of the effect of the active drug. Possibly the participating patients should not be given this information.