Pharmacologie de l’âme ou le mystère du placebo

Abstract

The "placebo" concept started with Saint Jerome's mistranslation of the first word of the ninth line of Psalm 116: instead of "I will walk before the Lord", he wrote "I will please the Lord" (Placebo Domino instead of ambulabo coram Domino). The placebo story is filled with quiproquos, mistakes and abuses. After many avatars, the placebo notion became firmly linked to medicine, and especially pharmacology. Nowadays, all new treatments are required to have proved their efficacy in randomized, placebo-controlled, double-blind trials. After a plethora of hypotheses based on psychology, behavorism, ethology, anthropology and sociology, proposing mechanisms of action based on patients' suggestibility and expectations induced by doctors' enthusiasm and beliefs, the past two decades have seen several new findings focusing on pharmacobiological phenomena. Animal studies provide fascinating information on immunological mechanisms and cancer outcomes in conditions of stress and pain. Placebo and nocebo mechanisms are now explained in terms of pain, endorphins, cholecystokinin and dopamine system activation, and possibly inflammation control. PET scans have been used to investigate these effects in depression and Parkinson's disease. A role of genetic mechanisms is also emerging in the field of placebo neurobiology. In fact, the placebo effect might simply result from the medical art. Further studies are needed to maximize the placebo effect and to make it more consistent.