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Background
The
origin of the word placebo is from the Latin verb "placere" which means
"to please". A placebo can be defined as an inert or inactive substance
(pill etc.) or procedure that has no known therapeutic effect. The
"placebo effect" is the improvement in the condition of a sick person that
occurs in response to treatment but cannot be considered due to the specific
treatment used (Websters).
The term placebo has been used
in connection with medicine for many years as is evident from this excerpt from
Hooper's Medical Dictionary (1811) that states a placebo is "an epithet
given to any medicine adapted more to please than benefit the patient".
The use of placebos as a control in clinical trials began in 1907 with a
un-blinded trial designed by W.H.R. Rivers to study the effects of alcohol and
other drugs on fatigue. The more widespread practice of double-blinded
placebo controlled trials as the gold standard for clinical trials began in the
1940's and 50's primarily through the work of the pharmacologist Harry Gold.
The FDA began recommending the use of double-blinded placebo controlled trials
"whenever ethical and feasible" in the 1970's.
The placebo effect was first
identified by Henry Beecher in the 1950's in a paper titled "The Powerful
Placebo" in which he examined 26 studies and found that an average of 35% of people responded
to placebo. Other studies have calculated the placebo effect to be much
higher, around 50-60%, and that the magnitude of the effect is dependent on the
ailment being treated. There is also a group of scientists and clinicians
that argue against the existence of a placebo effect. They propose that
the observations of Beecher and others are a result of poor methodological
thinking, inaccurate statistical interpretation of data or the combination of
multiple naturally occurring processes that may be confused with a "placebo
effect".
There are three major mechanisms have been proposed to explain the placebo
effect:
1.
The Opioid Model- the release of endorphins in response to the placebo stimulus.
Several studies have shown that patients reporting pain relief from a placebo
treatment report the return of pain following the administration of naloxone (an
opioid antagonist) (Fields). Proponents of this model suggest that the
administration of a placebo treatment leads to the release of endogenous
endorphins which lead to pain relief.
2.
The Conditioning Model- a learned response to medical intervention. This
model suggests that many people have experienced relief after taking a
medication. Therefore, the patient is conditioned to respond positively to any
medication administered to them, even if that medication is a placebo.
Animal studies have shown that a response similar to the placebo effect can be
elicited through conditioning.
3.
The Meaning or Expectancy Model- a consciously mediated response. This
model suggests that it is the meaning attached to a treatment or interaction
with a patient that is the driving force behind the placebo effect.
Proponents of this model suggest that the patients positive expectation of cure
and the interaction with the physician are extremely important in the patients
response to any treatment, placebo or not. Studies have shown decreased
pain and increased subjective rates of improvement in patients given positive
prognosis by a physician and treated with placebo when compared to patients who
received a negative prognosis and the same placebo treatment. |
