from Psychology, health and illness
Published online by Cambridge University Press: 18 December 2014
Overview
A placebo is a sham treatment that may be used clinically to placate a patient or experimentally to establish the efficacy of a drug or other medical procedure. The placebo effect is the effect produced by administering a placebo. In addition, active medications may produce placebo effects as well as drug effects and these may be additive. In this case, the placebo effect is that portion of the treatment effect that was produced psychologically, rather than through physical means.
Typically, placebos are physically inert substances which are identical in appearance to an active drug. Occasionally, active substances are used as placebos. Active placebos have side-effects that mimic those of the drug being investigated, but do not possess the physical properties hypothesized to produce the beneficial treatment effect. Active placebos are used to prevent patients from using the sensory cues provided by side effects to deduce the condition to which they have been randomized.
Placebo effects are not limited to drug treatments. Any medical procedure can have effects due to the physical properties of the treatment and effects due to its psychological properties. Just as the effects of the physical properties of a medication can be tested by comparing its effects to those of a sham medication, so too the physically produced effects of other medical procedures can be established by comparison with sham procedures (e.g. sham surgery).
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