American Cancer Society

Even though they don’t act on the disease, placebos affect how some people feel. This happens in up to 1 of 3 people. A change in a person’s symptoms as a result of getting a placebo is called the placebo effect. Usually the term “placebo effect” speaks to the helpful effects a placebo has in relieving symptoms. This effect usually lasts only a short time. It’s thought to have something to do with the body’s natural chemical ability to briefly relieve pain and certain other symptoms.