A placebo effect is an improvement in the symptoms of a disease or condition when a person is treated with a drug or other treatment that he or she expects to work, even though the treatment may not have been proved effective.

When a drug or treatment seems to work for some people but has not been scientifically proved to be any more effective than a "sugar pill" (placebo), it may be said to have a placebo effect. Active drugs and therapies can also have a placebo effect. It is sometimes hard to know if the reason a particular drug is working is because of its active ingredient or because of the placebo effect.

The placebo effect may be the result of the brain releasing "feel good" hormones such as endorphins in response to treatment. It may be part of the brain's attempt to heal the body. The placebo effect does not mean that a person's symptoms are imagined. But it does suggest that there is a strong connection between the mind and the body.