A placebo is a control substance (a dummy treatment) that can be given, if provided for in the protocol, to a group of patients participating in the study. It allows researchers to test for the ‘placebo effect’. This is a psychological response where people feel better even though the substance they are taking has no effect. By comparing people’s responses to the placebo and to the drug being tested, researchers can tell whether the drug is having any real benefit.
Source: EU Clinical Trials Register
