The necessity and the value of placebo.

The use of placebo in clinical trials has been repeatedly challenged as being unacceptable from an ethical point of view. The present paper responds to this criticism by taking up the issue in the light of the pertinent provisions of the Helsinki Declaration. Examples from different therapeutic areas are given that highlight the importance of placebo in situations in which its use is acceptable according to the Declaration. Particular emphasis is given to the question of active control trials, which, under conditions of low assay sensitivity, may become an ethically less acceptable approach than the use of a placebo control.