Placebo Effect

The placebo effect refers to the phenomenon by which an inert or inactive treatment (a placebo) nonetheless produces a beneficial effect for an individual by reducing or alleviating distress, usually due to psychological factors. This definition is problematic, however, as the use of inert or inactive to describe an intervention that produces an observable effect is a logical paradox. An alternative definition defines the placebo effect as a real effect (physiological or psychological, positive or negative) resulting from an intervention, but it cannot be attributed to any known element of that intervention. This definition avoids the “inert” paradox and broadens the scope to include negative consequences of receiving a placebo, such as a worsening of symptoms, sometimes called a “nocebo” effect. This entry focuses on ...