placebo /pləsē″bō/ [L, shall please] , an inactive substance, such as saline solution, distilled water, or sugar, or a less than effective dose of a harmless substance, such as a water-soluble vitamin, prescribed as if it were an effective dose of a needed medication. Placebos are used in experimental drug studies to compare the effects of the inactive substance with those of the experimental drug. They are also prescribed for patients who cannot be given the medication they request or who, in the judgment of the health care provider, do not need that medication.
