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Medically reviewed by L. Anderson, PharmD
Drugs.com
A placebo (or dummy pill) is an inert (inactive)
substance, typically a tablet, capsule or other dose form that does not contain
an active drug ingredient.
For example, placebo pills or liquids may contain
starch, sugar, or saline. Physical placebos, or “sham” treatments have also
been used, such as inactive acupuncture devices.
Placebos are often used in clinical trials as an
inactive control so that researchers can better evaluate the true overall
effect of the experimental
drug treatment under study.
In these clinical trials, one subset of patients
would receive the placebo and one group would receive the experimental drug,
but neither group is aware of which treatment they have received.
In addition, researchers in the study would not know
which patients have received active or placebo treatments.
These studies are called “double-blind” and
“placebo-controlled” and are considered the gold standard for experimental drug
research.
However, unexpected high placebo rates in clinical trials
can be detrimental, undermining the true effect of an active treatment.
Why are placebos used in drug
studies?
Conducting a double-blind, placebo-controlled
clinical trial helps to eliminate any bias that might occur due to knowledge of
who receives which treatments.
A patient or researcher would expect those who
receive the active drug to have a better outcome than those who did not, and
this knowledge can introduce bias into the study.
Typically, an experimental drug treatment needs to be
statistically more effective than the placebo to be considered as a valid drug
treatment.
Including a placebo group in a study is also
beneficial in evaluating treatment side effects.
However, many clinical trials, such as those in
cancer research, do not include placebo groups because it would not be
unethical to leave the patient’s cancer untreated.
In these trials, the experimental drug may be
compared to a treatment that is already FDA-approved instead of a placebo.
For example, in a 2018 study in The Lancet,
researchers looked at 21 antidepressants used for the acute treatment of adults
with major depressive disorder.
The antidepressants were either studied against
placebo or in head-to-head trials against each other.
Data were included from 522 trials with 116,477
participants in a systematic review and meta-analysis.
The researchers found that all antidepressants were
more effective than placebo in terms of effectiveness.
They also ranked different antidepressants based on
effectiveness and safety.
This data can inform clinicians who treat patients
with antidepressants that in fact they are more useful than using a placebo,
and in this case, helps to rank the active drugs based on effectiveness and
safety.
What is a placebo effect?
Research has shown that a placebo treatment can have
a positive therapeutic effect in a patient, even though the pill or treatment
is not active. This is known as the “placebo effect” or “placebo response”.
Placebo effects have been reported to occur in 21% to
40% of patients depending upon the study type.
For example, in pain studies utilizing brain imaging,
it has been shown that administration of a placebo to patients who believed
they were receiving an analgesic medication led to activation of the endogenous
opioid system in the brain.
Endogenous opioids, such as endorphins and
enkephalins, are natural pain-relieving chemicals produced in the body.
Analgesia due to the placebo effect is dependent upon
the activation of theses endogenous opioids in the brain.
It has also been shown that the placebo response in
patients with post-operative pain could be blocked by the opiate
antagonist naloxone,
further lending support to the placebo effect.
Dopamine, another central nervous system neurotransmitter,
has also been shown to be activated in the brain after placebo administration
to patients with Parkinson’s disease.
However, even when patients know they are receiving a
placebo, there may be beneficial effects.
A 2018 study in Scientific Review found
that an open-label placebo (OLP) may reduce fatigue in cancer survivors.
They compared OLP to treatment as usual (TAU) for
cancer survivors with fatigue in a 21-day randomized controlled trial.
The researchers found that participants in the placebo
group reported a 29% improvement in fatigue severity and a 39% improvement in
fatigue-disrupted quality of life compared to those randomized to TAU.
Similar reductions in fatigue and boosts in quality
of life were found when the TAU group was switched to the OLP for 21 days at
the end of the study.
Other studies have found differing results. A
Cochrane Review of 202 trials comparing placebo treatment with no treatment
reported that placebos produced no major health benefits, but did have a modest
effect on patient-reported outcomes, such as in pain and nausea, although
results were variable.
The authors explained that the observed variations in
the placebo effect could be explained by trial design differences and how
patients were informed of their treatments.
What is a nocebo effect?
A nocebo effect is the opposite of the placebo effect
-- a negative psychological effect of a treatment with no pharmacologic
activity.
This can occur when the placebo is administered and
accompanied by the suggestion that the patients ailment will get worse.
High nocebo effects can also interfere with
interpretation of clinical trial results.
Negative effects of drugs may be due to psychological
nocebo effects and not necessarily due to the drug itself.
It is ethical to use a placebo?
In clinical practice, physicians may prescribe
placebo treatments with or without the patients knowledge that they are
receiving an inactive therapy.
Psychologically, the patient may be encouraged that
they are receiving a treatment for their ailment that they believe will have
beneficial effect, and in turn the placebo may actually provide some relief.
However, the effect would not be due to a
pharmacological action attributed to the chemical composition of the medicine.
Placebos have been used in treatment of sleep,
anxiety, gastrointestinal disorders, chronic pain and
other disorders. The therapeutic use of placebo or sham treatments in medicine
is very controversial.
In one survey, only 3% of U.S. physicians reported using
actual sugar pills as placebos, but 41% said they had used over-the-counter
painkillers and 38 percent said they had used vitamins as placebos for their
patients.
Sixty-eight percent of physicians described the
placebo to their patients as a potentially beneficial medicine, and roughly
two-thirds of the doctors felt the practice was ethical.
In another study,
physicians used reduced doses of anti-inflammatory medications mixed in
combination with a placebo to successfully treat psoriasis patients.
Combining active drug with placebo may be effective
in diseases that involve the mental state and immune system, including:
· asthma
· multiple
sclerosis
· chronic pain.
Reducing doses of active drugs and combining with
placebo treatment could also reduce side effects, addiction potential and cost.
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