A placebo, as used in research, is an inactive substance or procedure used as a control in an experiment. The placebo effect is the measurable, observable, or felt improvement in health not attributable to an actual treatment.
When a treatment is based on a known inactive substance like a sugar pill, distilled water, or saline solution rather than having real medical value, a patient may still improve merely because their expectation to do so is so strong. To eliminate the effect of positive thinking on clinical trials, researchers often run double-blind, placebo-controlled studies.
In-Depth Explanation of the Placebo Effect:
Fast Facts About the Placebo Effect
The word placebo literally means "I will please" in Latin. The first known double-blind placebo-controlled trial was done in 1907. The FDA doesn't require that a drug study include a placebo control group, however, the placebo-controlled trial has long been the standard. The NIH is funding several studies related to the placebo effect.
Sources:
Placebo Effect, Robert Todd Carroll, The Skeptic's Dictionary, Skepdic.com
The Mysterious Placebo Effect, by Carol Hart, American Chemical Society
Modern Drug Discovery, July/August 1999
The Healing Power of Placebos, by Tamar Nordenberg, FDA Consumer magazine January-February 2000



