Placebo effect: Also called the placebo response. A remarkable phenomenon in which a placebo a fake treatment, an inactive substance like sugar, distilled water, or saline solution — can sometimes improve a patient’s condition simply because the person has the expectation that it will be helpful. Expectation to plays a potent role in the placebo effect. The more a person believes they are going to benefit from a treatment, the more likely it is that they will experience a benefit.

Reference : Medical Author: William C. Shiel Jr., MD, FACP, FACR,  https://www.medicinenet.com/script/main/art.asp?articlekey=31481 ,  consulted on july 1st,2019