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Placebo effect

The placebo effect is the phenomenon that a patient's symptoms can be
alleviated by a sham treatment, apparently because the individual expects or
believes that it will work. Some people consider this to be a remarkable
aspect of human physiology; others consider it to be an illusion arising
from the way medical experiments are conducted.

If patients complaining of back pain are administered only a placebo, for
example, typically about a quarter of them will report a relief or
diminution of the pain. Remarkably, not only do patients report improvement,
the improvements often are objectively measurable, and the same improvements
typically are not observed in patients who did not receive the placebo.

Because of this effect, government regulatory agencies approve new drugs
only after tests establish not only that patients respond to them, but also
that their effect is greater than that of a placebo (by way of affecting
more patients, by affecting responders more strongly or both). Such a test
or clinical trial is called a placebo-controlled study. Because a doctor's
belief in the value of a treatment can affect what his or her patient
believes, such trials are usually conducted in "double-blind" fashion: that
is, not only are the patients made unaware when they are receiving a
placebo, the doctors are made unaware too. Recently, it has even been shown
that "mock" surgery can have similar effects, and so some surgical
techniques must be studied with placebo controls (rarely double blind, for
obvious reasons).

The size of the placebo effect is controversial. A part of the controversy
may be due to the fact that patients who have been given a drug (or a
placebo for that matter) will oftentimes report improvement earlier and more
eagerly in order to please and thank the care giver. These patients may even
do this when there is no real physical improvement attained. Hence, the
uncertainty over the real size of the placebo effect. An often quoted number
is that about one third of patients improve on a placebo, but a recent study
has called that number into question, claiming that the effect is much
smaller, if it exists at all.

It has been argued that the placebo effect may be simply an experimental
artefact that arises because the patients in any study are selected to show
a particular characteristic (symptom of illness). Since the sample is thus
initially skewed away from the mean, it is likely that during the course of
the study there will be a natural tendency for the sample to revert towards
the mean - i.e. show better than average levels of recovery.

The reverse effect, sometimes called the Nocebo Effect, is the result of
negative expectations by the patient. Some patients who believe that they
should be ill can exhibit genuine symptoms.

The Nocebo Effect may or may not be distinguished from older concepts such
sociogenic illness or psychosomatic illness. In any case, distinguishing
between these effects can be a difficult problem for medical semiotics, or
the study of how to interpret the patient's description of their ailments.

The strictest definition would be the negative effect produced by an
expectation that a medicine or treatment does not work in general or for the
patient in particular. Sociogenic illness and psychosomatic illness might
therefore be broader terms where a known or unknown cause with cultural or
psychological factors is involved.

Example: I believe that cough medicine does not work. I suffer, therefore,
from the Nocebo effect--the medicine is less effective for me than for a
patient who believes the medicine actually prevents coughs.

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