Stacey Carter, age 15, of Gadsden, Ala., for her question:

WHAT IS A PLACEBO?

A placebo in medicine is an inert substance, such as sugar, that is used in place of an active drug. Here's how you pronounce the word: plaa sea bow.

In testing new drugs, placebos are used to avoid bias. That is, in a blind test, patients do not know if they have been given the active drug or the placebo. In a double blind test, doctors observing the result also do not know.

Placebos may be administered to some patients who have incurable illnesses in order to induce the so called placebo effect: an improvement, at least temporarily, of the patient's condition.

In tests, it was found that up to 35 percent of the patients can improve by receiving placebos. Little is understood of how this effect works, but one theory is that the patient's faith in a cure may be related to the release of brain chemicals called endorphins, the body's natural opiates.

Sometimes the effect of placebos is negative, however, if hopes have been raised too high.