When scientists want to test the effectiveness of a new drug, they usually divide a large number of people into two groups. One group takes the medicine that is being tested. The other group takes an inactive substance, called a placebo（安慰劑）. Placebo pills are usually made of sugar.

None of the people know which pill they are taking -- the active one or the inactive one. In this kind of experiment, the medicine must perform better than the placebo to prove it is effective.

The word "placebo" is Latin. It means "I shall please." And, sometimes, it just might do that. Some people who take the placebo report improvements in their health. This is known as the "placebo effect" -- the effect of something that is not supposed to have any effect.

Some doctors have reported the use of the placebo effect in treatment. For example, a doctor tells a patient that a new drug will stop his or her pain. The pill is only sugar. The patient does not know that. The patients takes the pills and reports that the pain is gone.

An influential study appeared in nineteen-fifty-five. It said treatment with a placebo made patients feel better thirty-five percent of the time. In two-thousand-one, Danish researchers reported that they had examined more than one-hundred studies. They found little evidence of healing as a result of the use of placebos. Other scientists disputed those findings.

But some medical researchers do think it is wrong to use inactive substances when testing new drugs. They say it would be better to use existing drugs instead of placebos and see if the new drug is more effective.

Other researchers are looking at the placebo effect in connection with the use of real drugs for conditions like asthma and high blood pressure. They want to prove whether a drug works better if a doctor provides it cheerfully and tells the patient that it will help. They say a good relationship between a patient and a doctor may increase the effectiveness of the drugs that the doctor provides.

Doctors say investigating the placebo effect is important for the future of medicine. They say the knowledge gained may make it possible to reduce the number of drugs people need to take to improve their health.

This VOA Special English Health Report was written by Nancy Steinbach. This is Phoebe Zimmermann.