Placebo

Placebo: a treatment without substantive content.

Placebo effect: temporary relief obtained with a placebo.

A placebo is any treatment that has no substantive content. In other words, it is a treatment, which can be a medication (e.g. a pill, fluid, powder, inhalant, injection, ointment, etc.), something administered with a machine (e.g. a sound, electric current, light, etc.), or anything else that, as far as the person administering the treatment knows, has no effect on the complaint that it is supposed to treat. Typical placebo may be flour, sugar, colored light, etc. The form of the placebo is chosen either for its dramatic appearance in order to assess the psychological factors involved in the response of a person believing that a palliative or a curative treatment is being given, or to resemble that of the factual treatment. The true response to a factual treatment is determined by subtracting the effect of the placebo. For instance, if 40 percent of patients receiving the placebo report feeling better (or sleeping better, or eating less, or having less pain, etc.), and the same is true of the putative factual treatment, then the conclusion would be that the treatment is no better than the placebo, i.e., that it has no demonstrable effect. However, if the factual treatment yielded an 80 percent improvement rate compared to 40 percent for placebo, then it would be concluded that the factual treatment was effective. Further, relief provided by placebo typically subsides within a few months or less. Relief provided by factual treatment may be expected to last longer or indefinitely. Therefore, a prolonged study may be more likely to identify factual treatment that is effective only in some people.

The "placebo effect" is the term used to describe both the effect of placebo used in a comparative trial of a factual treatment and in describing the apparent efficacy of anything used by a person in expectation of benefit or relief, including situations with no medicinal implications. For instance, switching to a different financial manager may be associated with a feeling of relief ahead of any factual demonstration of improved performance. However, its most common usage applies in relation to people with chronic complaints who purchase successive "tonics", each of which seems to benefit them for a short while, then appears to become ineffective and has to be replaced with something new. The placebo effect in the first few weeks of treatment often affects 20 to 40 percent of those treated.