A placebo is defined as a harmless medicine given for the psychological benefit of the patient. The placebo effect is the phenomenon whereby a placebo — a fake treatment, an inactive substance like sugar pills, or a sham procedure — can sometimes improve a patient's condition simply because the patient believes that it will. The placebo effect has been well-documented in medical research. In one famous study, patients with angina were given either a placebo or a real drug. Both groups improved, but the group given the placebo improved more. The mechanisms underlying the placebo effect are not well understood. It is clear that the effect is at least partially due to the power of suggestion: if patients believe that a treatment will help them, it often does. The placebo effect may also be due to the body's own healing mechanisms. When patients receive a placebo, they may produce more endorphins, natural pain-killing chemicals, in response to the expectation of pain relief. The placebo effect is an important phenomenon with implications for both patients and doctors. Patients should be aware that the power of suggestion can be a powerful tool in the healing process. And doctors should be aware that the placebo effect is a real phenomenon that can influence the outcome of treatment.