Lessons from placebo effects in migraine treatment.

In medical research, the placebo effect is an important methodological tool. Placebo is given to participants in clinical trials, with the intention of mimicking an experimental intervention. The "nocebo" effect, on the other hand, is the phenomenon whereby a patient who believes that a treatment will cause harm actually does experience adverse effects. The placebo effect strongly influences the way the results of clinical trials are interpreted. Placebo responses vary with the choice of study design, the choice of primary outcome measure, the characteristics of the patients and the cultural setting in which the trial is conducted. In migraine trials, the placebo response is high, in terms of both efficacy and side effects. Although medical ethics committees are becoming increasingly resistant to the use of placebo in acute migraine trials, placebo nevertheless remains the pivotal comparator in trials of migraine medications.