Placebo is something used in experiments to proove that a drug for example is effective. In these experiments several people are summoned, a group receives the drug in question and the other group the placebo that is a substance (or the inactive drug) with no positive or negative effect on health. The participants in the clinical trial don’t know if they receive the real thing or the placebo. Researchers can measure if the drug works by comparing how both groups react. In this way the effectiveness of the drug is tested in comparison with the placebo.
Sometimes a person can have a response to a placebo and so the placebo effect occurs. For instance the person may have what appears to be side effects from the treatment (positive effect). Your mind can be a powerful healing tool when given the chance, your brain can convince your body a fake treatment is the real thing. Some people can experiment a negative effect and symptoms may improve.