Measurable or perceived improvement in health which cannot be attributed to an actual medical treatment. Placebo is a Latin word meaning “I shall please”. A placebo is something that does not change anything chemically such as the commonly known sugar pills or saline solution.
Placebo research has shown that a significant amount of sicknesses can be cured purely by the person’s belief that they are receiving a clinical treatment. Some ailments that have been cured by placebos include: pain symptoms, depression, a few heart conditions, ulcers (gasteric variety) and other stomach issues. This improvment leads many people to believe that sickness is all in the head.
Example: Many researchers run double-blind studies with both a treatment group and a placebo (non-treatment) group, in order to eliminate the potential effect of positive thinking on the clinical trial.
If you would like to read more about placebo studies, history etc, here is an interesting website: http://www.skepdic.com/placebo.html