A placebo (/pləˈsiːboʊ/ plə-SEE-boh) can be roughly defined as a sham medical treatment. Common placebos include inert tablets (like sugar pills), inert injections (like saline), sham surgery, and other procedures.
Placebos are used in randomized clinical trials to test the efficacy of medical treatments. In a placebo-controlled trial, any change in the control group is known as the placebo response, and the difference between this and the result of no treatment is the placebo effect. Placebos in clinical trials should ideally be indistinguishable from so-called verum treatments under investigation, except for the latter's particular hypothesized medicinal effect. This is to shield test participants (with their consent) from knowing who is getting the placebo and who is getting the treatment under test, as patients' and clinicians' expectations of efficacy can influence results.
