Illustrated Glossary of Organic Chemistry

Placebo: A substance without therapeutic benefit given instead of the drug being tested in a clinical trial. This is done to ensure that trial participants -- both the trial's subjects/patients and administrators -- are unaware of which subjects are receiving the drug being tested and which are not. Such knowledge might bias interpretation of the data produced by the clinical trial.

In a clinical trial of the anticancer drug paclitaxel, some patients will receive the therapeutically-active drug while other patients will receive a therapeutically-inactive placebo such as sucrose.