[Placebo and placebo effects (second part) : ethical aspects].

The use of placebo is controversial. It is generally accepted when no treatment exists for the disease under study but a polemic persists when a therapy is already regularly applied by medical practitioners. The paper cites and comments on the publications of national and international institutions (Belgian Medical Board, World Medical Association, Council for International Organizations of Medical Sciences) on this topic. The pros and cons about the use of placebo in clinical research are presented. Each protocol, with or without placebo has to abide by the general principles of medical ethics whose requirements may sometimes be contradictory. In these circumstances, the investigators must find a compromise acceptable morally and scientifically and submit it to ethics committees which have to decide about the validity of their arguments.