toxicologist: one who studies the nature and effects of poisons and their treatment
scientist: a person with advanced knowledge of one or more sciences
placebo effect: any effect that seems to be a consequence of administering a placebo; the change is usually beneficial and is assumed result from the person's faith in the treatment or preconceptions about what the experimental drug was supposed to do; pharmacologists were the first to talk about placebo effects but now the idea has been generalized to many situations having nothing to do with drugs