Placebo

A placebo (/pləˈsiːboʊ/ plə-SEE-boh) can be roughly defined as a sham medical treatment.^[1] Common placebos include inert tablets (like sugar pills), inert injections (like saline), sham surgery,^[2] and other procedures.^[3]

Placebos are used in randomized clinical trials to test the efficacy of medical treatments, so they serve as epistemological tools to screen out the ‘noise’ of clinical research. Placebos in clinical trials should ideally be indistinguishable from so-called verum treatments under investigation, except for the latter’s particular hypothesized remedial factor(s).^[4] This is to prevent the recipient or others from knowing (with their consent) whether a treatment is active or inactive, as expectations about efficacy can influence results.^[5][6]

Placebos are also popular because they can sometimes produce relief through psychological mechanisms (a phenomenon known as the "placebo effect"). They can affect how patients perceive their condition and encourage the body's chemical processes for relieving pain^[7] and a few other symptoms,^[8] but have no impact on the disease itself.^[9][7]

Improvements that patients experience after being treated with a placebo can also be due to unrelated factors, such as regression to the mean (a statistical effect where an unusually high or low measurement is likely to be followed by a less extreme one).^[7] The use of placebos in clinical medicine raises ethical concerns, especially if they are disguised as an active treatment, as this introduces dishonesty into the doctor–patient relationship and bypasses informed consent.^[10]

In a placebo-controlled clinical 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.^[11] Some researchers now recommend comparing the experimental treatment with an existing treatment when possible, instead of a placebo.^[12]

The idea of a placebo effect was discussed in 18th century psychology,^[13] but became more prominent in the 20th century. Modern studies find that placebos can affect some outcomes such as pain and nausea, but otherwise do not generally have important clinical effects.^[9]