A placebo ( ) 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, 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). 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.
Placebos are also popular because they can sometimes produce relief through psychological mechanisms (phenomenon known as "placebo effect"). They can affect how patients perceive their condition and encourage the body's chemical processes for relieving pain and a few other symptoms, but have no impact on the disease itself.
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). 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. While it was once assumed that this deception was necessary for placebos to have any effect, there is some evidence that placebos may have subjective effects even when the patient is aware that the treatment is a placebo (known as "open-label" placebo).
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. Some researchers now recommend comparing the experimental treatment with an existing treatment when possible, instead of a placebo.
The idea of a placebo effect—a therapeutic outcome derived from an inert treatment—was discussed in 18th century psychology, but became more prominent in the 20th century. An influential 1955 study entitled The Powerful Placebo firmly established the idea that placebo effects were clinically important, and were a result of the brain's role in physical health. A 1997 reassessment found no evidence of any placebo effect in the source data, as the study had not accounted for regression to the mean.
Etymology
Placebo (pronounced /plaˈkebo/ or /plaˈt͡ʃebo) is Latin for [I] shall be pleasing. It was used as a name for the Vespers in the Office of the Dead, taken from its incipit, a quote from the Vulgate's Psalm 116:9, placēbō Dominō in regiōne vīvōrum, "[I] shall please the Lord in the land of the living." From that, a singer of placebo became associated with someone who falsely claimed a connection to the deceased to get a share of the funeral meal, and hence a flatterer, and so a deceptive act to please.
Definitions
The definition of "placebo" has been debated. One definition states that a treatment process t is a placebo when none of the characteristic treatment factors C are effective (remedial or harmful) in patient X for disease D.
In a clinical trial, a placebo response is the measured response of subjects to a placebo; the placebo effect is the difference between that response and no treatment. The placebo response may include improvements due to natural healing, declines due to natural disease progression, the tendency for people who were temporarily feeling either better or worse than usual to return to their average situations (regression toward the mean), and errors in the clinical trial records, which can make it appear that a change has happened when nothing has changed. It is also part of the recorded response to any active medical intervention.
Measurable placebo effects may be either objective (e.g. lowered blood pressure) or subjective (e.g. a lowered perception of pain).
Effects
Placebos can improve patient-reported outcomes such as pain and nausea but also objective outcomes such as motor functions and immune/endocrine parameters.