The achievement of optimal therapeutic results presupposes the use of appropriate treatment combined with maximal utilization of placebo effects. These aims may sometimes be difficult to satisfy in randomized clinical trials (RCTs). The question thus arises whether there is a conflict between the goals of therapy and those of experimental research; and if so, to what extent, and how is it handled in practice by clinicians and researchers. Various ethical problems have been discussed in several reports connected with RCTs. But we have found no discussion concerning the conflict between obtaining informed consent and promoting optimal placebo effects. Information about RCTs can be given in various ways. Sometimes appropriate information about RCTs to patients involves non-optimal utilization of placebo effects. This gives rise to ethical and methodological problems, which are discussed in this article.