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What is a placebo effect?
A placebo (pluh-see-bow) is a substance or other kind of
treatment that looks just like a regular treatment or medicine, but it
is not. It is actually an inactive "look-alike" treatment or substance.
This means that it is not a medicine. The person who is getting a
placebo does not know he or she is getting one. Sometimes the placebo
is in the form of a "sugar pill," but a placebo can also be an
injection, a liquid, a procedure, or any other type of therapy that
doesn't directly affect the illness being treated.
Even though placebos do not act on the disease, they seem to
have an effect in about 1 out of 3 patients. A change in a person's
symptoms as a result of getting a placebo is called a placebo effect.
Usually the term placebo effect speaks to the helpful effects of a
placebo in relieving symptoms. This effect usually lasts only a short
time, and is thought have something to do with the body's own chemical
ability to briefly relieve pain or certain other symptoms.
But sometimes the effect goes the other way, and causes
unpleasant or worse symptoms. These may include headaches, nervousness,
nausea, or constipation, to name a few. The unpleasant effects that
happen after getting a placebo or an inactive treatment are sometimes
called the nocebo effect.
Together, these 2 types of outcomes are sometimes called expectation effects.
This means that the person taking the placebo may experience something
along the lines of what he or she expects to happen. If a person
expects to feel better, that may happen. If the person believes that he
or she is getting a strong medicine, the placebo may be thought to
cause the side effects. The placebo does not cause any of these effects
directly. Instead, the person's belief in or experience of the placebo
helps cause the change in symptoms.
Along with the placebo or nocebo effect, incidental events
(unrelated effects that may have happened without the placebo) may also
be linked to the placebo because of their timing. For example, a
headache or rash that happens soon after taking a placebo may be caused
by something else entirely, but the person may think the placebo caused
it. The same can be said for good outcomes: if a person happened to
start feeling better after taking a placebo, that improvement may be
thought to be caused by the placebo.
Some patients can have a placebo effect without getting a
pill, shot, or procedure. Some may just feel better from visiting the
doctor or doing something else they believe in. That type of placebo
effect seems most related to the degree of confidence and faith the
patient has in the doctor or activity.
How are placebos used?
Placebos are often used in clinical trials to test new drugs
or treatments. Clinical trials are research studies testing new drugs
or other treatments in people. Before a new treatment is used on
people, it is studied in the lab. If lab studies suggest the treatment
will work, the next step is to test it on animals. If that also gives
promising results, it may then be tested in clinical trials to see if
it has value for patients. The main questions the researchers want to
answer are:
- Does this treatment work?
- Does it work better than what we're now using?
- What side effects does it cause?
- Do the benefits outweigh the risks?
- Which patients are most likely to find this treatment
helpful?
If standard treatments for the disease are already available,
the new treatment is usually compared to one of these treatments. This
tells researchers if the new treatment is as good as or better than the
one that is currently available. If you would like to know more about
clinical trials, see our document Clinical Trials: What You Need
to Know.
If there is no approved treatment for an illness or condition,
some people in the study may be given a placebo, while others get the
new treatment being tested. The main reason to have a placebo group is
to be sure that any effects that happen are actually caused by the
treatment and not some other factor. The placebo looks, tastes, or
feels just like the actual treatment, so that the patient's
expectations alone are not responsible for the outcome. In a
"double-blind controlled study," neither the people taking part in the
study nor their doctors know who is getting which treatment. This study
design helps avoid biases in measuring outcomes that can be caused by
the researchers' expectations about the treatment.
People in a study that involves a placebo should always know
that there is a chance they could be getting a placebo. It is not OK to
give someone a treatment in a clinical trial and not mention that it
could be a placebo. Our document Informed Consent
gives you more information on this topic.
Those who get placebos in medical studies serve an important
role. Their responses help provide a good way to measure the effect of
the treatment being tested. The placebo group provides an important
baseline to compare the treatment group against. It helps researchers
see what would have happened without the treatment, though the placebo
group may still have some short-term effects based on what the patient
expects. For instance, illnesses that sometimes go away on their own
might be thought to get better because of the medicine, unless there is
a placebo group and those people also get better. On the other side,
bad effects that were going to happen anyway, or that occur from some
unrelated cause, may be blamed on the treatment unless they also happen
to people in the placebo group.
How does the placebo effect work?
In the past, some researchers have questioned whether there is
convincing proof that the placebo effect is a real effect. But there
are studies showing that the placebo effect is real. For example,
scientists have recorded brain activity in response to placebo.
Many think the placebo effect occurs because the patient
believes in the substance, the treatment, or the doctor. The patient's
mind somehow causes other physical changes in the body over the short
term. The patient expects to feel better, and so he or she does feel
better. But even if a person feels better after taking a placebo, it
doesn't mean the person's illness or symptoms were not real.
Since many scientific tests have shown the placebo effect, it
is one way we know for sure that the mind and body are connected. Some
scientific evidence suggests that the placebo effect may be partly due
to the release of endorphins in the brain. Endorphins are the body's
natural pain killers. But there is probably more to it than this.
What is commonly called the placebo effect even plays a role
in mainstream medicine. Many people feel better after they get medical
treatments that they expect to work. But the opposite can also happen,
and this seems to support the idea of the expectation effect even more.
For example, in one study, people with Alzheimer's disease were less
affected by pain medicines, and required higher doses--possibly because
they had forgotten they were getting the drugs, or that the pain
medicines had worked for them before.
This suggests that past experiences also play into the placebo
effect. In one study that looked at the placebo effect in pain relief,
one group got a real pain medicine and the other did not. In the
following days, both groups were given a placebo that looked like the
real pain medicine. Those who had gotten the real pain medicine were
able to tolerate more pain than those who had not gotten pain medicines
before. In the same study, people who were given a drug that raised a
certain hormone level beforehand actually had a similar (but smaller)
hormone response when they were given a placebo later. Those who had
not gotten the real drug beforehand had no change in their hormone
levels when they got the placebo, even though they were told that they
would. This helped to separate out the power of the researcher telling
them they would have an effect from the learned experience of having
the effect in the past. This type of learned response after personal
experience is called the conditioning
effect. It seems to be part of what we call the placebo
effect.
The nocebo effect, in which a person has more symptoms or side
effects after a placebo, is still being studied as well. Researchers
believe it may be partly explained by a substance in the body that
sends messages through the nerves. When a person is anxious, the
substance is activated, and the person feels more pain than a person
who isn't anxious. It also affects the brain: brain-imaging studies
have shown that pain is more intense when a person expects more pain
than when there is a neutral expectation. This is linked to changes in
certain brain regions on the imaging studies.
Although we may not know exactly how it works, the idea that
the mind can affect the body has been around for years and is
well-proven in certain situations. Many ancient cultures depended on
mind-body connections to treat illness. Shamans or medicine men would
not have viewed their efforts as placebos. But their healing powers may
have worked in the same way, partly through the patient's strong belief
that the shaman's treatments would restore health. Or it could be that
the sick person was going to get better anyway, but the recovery was
thought to be because of the treatment--which may have really done
nothing for the illness.
Because placebos often have an effect, even if it does not
last long, some people think that the placebo produced a "cure." But
placebos do not cure. And in studies where doctors are looking at
whether a tumor shrinks, placebos would be expected to have very
little, if any, effect on cancer growth.
Still, placebos clearly can help relieve certain symptoms such
as pain, anxiety, and trouble sleeping in some people. In earlier
times, placebos were sometimes given by doctors out of frustration or
desperation, because nothing else was available or seemed to work.
Sometimes if the placebo looks more "real," the person may
think it is an active medicine or treatment and believe in its power
even more. For example, a larger pill may look more powerful than a
small pill. In some people, an injection may have a stronger placebo
effect than a pill.
Some believe that placebos seem to work because many illnesses
improve over time even without treatment. People may also take better
care of themselves by exercising, eating healthier, or resting if they
are taking a placebo. Just as natural endorphins may relieve pain once
they are released, some research shows the brain may respond to an
imagined scene much as it would to something it actually sees. A
placebo may help the brain remember a time before the symptoms and
bring about a chemical change. This is a theory called remembered wellness.
Some scientists believe that the effects of many alternative
therapies may simply be a placebo effect. If the patient believes in
the treatment and wants it to work, it can seem to do so, at least for
a while. If this effect worked on an illness that usually would not get
better on its own, and it lasted, it would be considered a real cure,
not a placebo.
There is still much to find out about the placebo effect and
all the ways it may work. Researchers continue to study it in order to
learn more about it, and whether it may be used to help people feel
better.
Additional resources
More information from your American Cancer
Society
The following related information may also be helpful to you.
These materials may be viewed on our Web site or ordered from our
toll-free number, 1-800-227-2345.
Along with the above, information on many different types of
complementary and alternative treatments are available at no cost to
you from the American Cancer Society. You can find them on our Web site
or request from our toll-free number as noted above.
Other organizations and Web sites*
Today there is a great deal of interest in complementary and
alternative therapies. Mass communication, especially the Internet,
makes it possible for people to share ideas and information very
quickly. But too often information on the Internet is written by
promoters of useless treatments. Along with the American Cancer
Society, the following is a partial list of Web sites and phone numbers
of reputable groups that provide information on complementary and
alternative therapies:
National Cancer
Institute
Web site: www.cancer.gov
Toll-free number: 1-800-422-6237 (1-800-4-CANCER)
TTY: 1-800-332-8615
National Center
for Complementary and Alternative Medicine (NCCAM)
Web site: http://nccam.nih.gov
Toll-free number: 1-888-644-6226
TTY: 1-866-464-3615
Memorial Sloan
Kettering Cancer Center
About Herbs and Botanicals
Web site: www.mskcc.org/mskcc/html/11570.cfm
The University
of Texas MD Anderson Center
Complementary/Integrative Medicine Therapies
Web site: www.mdanderson.org/cimer
United States
Department of Agriculture, Food and Nutrition Information Center
Web site: http://fnic.nal.usda.gov
Choose "Dietary Supplements" from the left menu bar
United States
Food and Drug Administration
Web site: http://vm.cfsan.fda.gov/%7Edms/supplmnt.html
Toll-free number: 1-888-INFO-FDA (1-888-463-6332)
To report side effects or other adverse events from a dietary
supplement, call Medwatch at 1-800-FDA-1088
National Council
Against Health Fraud
Web Site: www.ncahf.org
Quackwatch
Web Site: www.quackwatch.org
*Inclusion on
this list does not imply endorsement by the American Cancer Society
No matter who you are, we can help. Contact us anytime, day or
night, for information and support. Call us at 1-800-227-2345 or visit www.cancer.org.
References
Benedetti F, Arduino C, Costa S, et al. Loss of
expectation-related mechanisms in Alzheimer's disease makes analgesic
therapies less effective. Pain.
2006;121:133-144.
Benedetti F, Pollo A, Lopiano L, et al. Conscious expectation
and unconscious conditioning in analgesic, motor, and hormonal
placebo/nocebo responses.
J Neurosci. 2003 May 15;23(10):4315-23.
Beyerstein BL. Distinguishing science from pseudoscience.
1995. Victoria, B.C.: The Centre for Curriculum and Professional
Development. Accessed at:
www.sfu.ca/~beyerste/research/articles/02SciencevsPseudoscience.pdf
onNovember 8, 2007.
Colloca L, Benedetti F. Nocebo hyperalgesia: how anxiety is
turned into pain. Curr
Opin Anaesthesiol. 2007 Oct;20(5):435-9.
Colloca L, Benedetti F. Placebo analgesia induced by social
observational learning. Pain.
2009 Mar 9.
Haour, F. Mechanisms of the placebo effect and of
conditioning. Neuroimmunomodulation.
2005;12:195-200.
Hrobjartsson A, Gotzsche PC. Is the placebo powerless?
Systematic review with 52 new randomized trials comparing placebo with
no treatment. Journal
of Internal Medicine. 2005;257:394-396.
Kaptchuk TJ. The placebo effect in alternative medicine: Can
the performance of a healing ritual have clinical significance? Ann Intern Med.
2002;136:817-825.
Kaptchuk TJ, Kelley JM, Conboy LA, et al. Components of
placebo effect: randomised controlled trial in patients with irritable
bowel syndrome. BMJ.
2008 May 3;336(7651):999-1003.
Link J, Haggard R, Kelly K, Forrer D. Placebo/nocebo symptom
reporting in a sham herbal supplement trial. Eval Health Prof.
2006;29:394-406.
Pollo A, Amanzio M, Arslanian A, et al. Response expectancies
in placebo analgesia and their clinical relevance. Pain. 2001
Jul;93(1):77-84.
Wampold, BE, Minami T, Tierney SC , Baskin TW, Bhati, KS. The
placebo is powerful: Estimating placebo effects in medicine and
psychotherapy from randomized clinical trials. Journal of Clinical Psychology.
2005;61:835-854.
The Australian Psychological Society. Placebo effect. Last
updated March 2006. Accessed at:
www.betterhealth.vic.gov.au/bhcv2/bhcarticles.nsf/pages/Placebo_effect?OpenDocument
on December 13, 2007.
Scott DJ, Stohler CS, Egnatuk CM, et al. Individual
differences in reward responding explain placebo-induced expectations
and effects. Neuron.
2007;55:325-336.
Wager TD, Rilling JK, Smith EE, et al. Placebo-induced changes
in fMRI in the anticipation and experience of pain. Science.
2004;303:1162-1167.
Last Medical Review: 06/11/2009
Last Revised: 06/11/2009
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