What is a placebo?

A placebo is a dummy treatment — for example, a tablet that looks identical to the real medicine but contains no active ingredient.

Researchers sometimes compare a new treatment against a placebo so they can be sure any benefit really comes from the treatment and isn't simply the result of taking part in a study.

If a trial uses a placebo, the team will explain this clearly before you decide whether to take part. In serious illness, the comparison is more often the current standard treatment rather than a placebo.