Understanding and harnessing placebo effects: clearing away the underbrush.

Despite strong growth in scientific investigation of the placebo effect, understanding of this phenomenon remains deeply confused. We investigate critically seven common conceptual distinctions that impede clear understanding of the placebo effect: (1) verum/placebo, (2) active/inactive, (3) signal/noise, (4) specific/nonspecific, (5) objective/subjective, (6) disease/illness, and (7) intervention/context. We argue that some of these should be eliminated entirely, whereas others must be used with caution to avoid bias. Clearing away the conceptual underbrush is needed to lay down a path to understanding and harnessing placebo effects in clinical medicine.