placebo

: a pill or substance that is given to a patient like a drug but that has no physical effect on the patient

◊ Patients who have been given a placebo that they think is a real drug may feel better because they believe that they are getting actual medicine. The improvement that they experience in their health is called the placebo effect. Placebos are also used in tests to compare the effect of a real drug with a substance that does not have any physical effect.