A placebo is a 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.
It is important to understand that not all placebo effects are good. Just as some patients improve with the power of positive thinking, some get worse and drop out of research studies because of the side effects caused by the placebo. In a recent, well-publicized and fascinating study of Parkinson disease, it was discovered that the patients who improved with placebo had changes in their brain that were identical to the changes caused by the actual medication. Levodopa causes an increase in brain dopamine, and the placebo should not. However, the patients who got better with placebo had a similar increase in dopamine, identical to what happened in those who were given the drug.
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