It is an effect where you experience a positive or negative effects from an inactive "look-alike" substance or treatment. The inactive substance is called the placebo. The mind has a powerful influence on the body and expectations can trigger this effect. More the expectations more they can feel it. The effects are less prominent on people who don't believe that the medicine or treatment is going to help them. Placebo effect is extensively used in medical research. Test subjects are given either the actual medicine under trial or the placebo. This will help get a more accurate idea on the efficacy of the medicine. To take this one step further, these studies can be done in a double blind way. In a double blind study, neither the researchers nor the test subjects know what treatment they are getting. This helps reduce the bias in the study due to placebo effect.
