In 25% of all cases where people go to see their
doctors because of pain, that pain is chronic, which goes to show just how prevalent
chronic pain is. Back pain is the leading type of chronic pain, followed by headaches,
pain in the joints, and then a wide range of various types of chronic pain in
the abdomen, the chest, and other parts of the body.
on chronic pain are staggering. The International Association for the
Study of Pain reports that about 20% of the world’s population —one
out of every five people—suffers from chronic pain.
the most conservative estimates, in the United States alone, about 50 million
people experience chronic pain, and the resulting costs of treatment and lost
productivity run to about $125 billion each year.
Chronic pain affects
the same proportion of the population in Canada and Europe as well, and its prevalence
increases with age. According to one pan-Canadian study, in Quebec, the prevalence
of chronic pain among men and women over age 65 is nearly 40%.
75 million people have been living with pain for more than seven years, and one-fifth
of them for over 20 years without having managed to find the relief they need.
As a result, 21% of these people living with chronic pain have also been diagnosed
In 2004, a survey by the American Chronic Pain Association
showed that more than half of all people with chronic pain regarded their ability
to work as compromised. The Chronic Pain Association of Canada reports that people
who have chronic pain miss an average of 16 days of work per year.
45% of all people with chronic pain experience a deterioration in their personal
relationships as a result. Hence it is no surprise that, according to a study
published in January 2006, nearly 14% of all Quebeckers who have chronic pain
make a suicide
attempt. In this case, the problem is not so much a lack of effective treatments
as a lack of resources to provide them and of adequate access to them. For example,
statistics published in 2005 indicate that at that time, at least 4 500 Quebeckers
with chronic pain were waiting for their initial assessment in a specialized pain
clinic, and two-thirds of them had been waiting for more than nine months.
The pain associated with cancer
can be either acute or chronic. Acute pain can result from cancer treatments (surgery,
chemotherapy, radiation therapy), while chronic pain can occur, for example, when
the tumour presses on a nerve, or releases certain
chemicals, or interferes with the flow of blood or the functioning of internal
Various data seem to indicate that the pain caused by cancer has
a negative effect on the immune system, which could indirectly encourage the growth
of the tumour. That is one reason why it is so important for both the acute pain
and the chronic pain associated with cancer to be treated immediately.
As the terms “acute
pain” and “chronic pain” suggest, the main criterion for making
this distinction is the duration of the pain. Acute pain may last anywhere from
a few seconds to several months, but eventually it disappears once the healing
process is completed. In contrast, pain is regarded as chronic if it persists
beyond the normal healing time and continues for more than three to six months
(though it may change in some ways over this time). Chronic pain can result from
an injury that does not heal properly, or from a host of other causes, such as
cancer, nerve damage, or arthritis.
Detail of Andromache Mourning Hector,
by Jacques-Louis David, 1783, oil on canvas, Musée du Louvre, Paris
But before venturing into the complexities
of chronic pain, let’s discuss acute pain in more detail.
Acute pain consists of sharp, immediate sensations of pain in response to a specific
tissue injury. Acute pain is highly localized and is accompanied by autonomic
reactions (such as sweating and increased heart and respiration rates) and motor
reactions (such as the withdrawal
Acute pain can range from
the simple pain of an insect bite, to post-surgical pain, to pain from an infection,
burn or fracture, which may last for several months. But in all cases, acute pain
is a symptom that gradually fades away as the illness is cured or the wound heals.
But sometimes pain
becomes chronic. In such cases, pain no longer seems to have any connection
with its primary function of protecting the body, and there is no longer any clear
relationship between the nature of the physical injury and the intensity of the
pain. Chronic pain inevitably degrades people’s quality of life and can
even alter their personalities, interfere with their work, and affect their personal
Living for more than six
months, or sometimes even several years, with a chronic backache (see box below)
or recurrent migraines
can be extremely disabling. In the worst cases, people can no longer perform routine
tasks, because it is so hard for them to concentrate on anything besides their
pain. Chronic pain can lead to insomnia,
anger, distress, and even depression.
When people are in chronic pain, depression
can amplify it, thus depressing their mood even further. Everything possible should
be done to prevent this vicious cycle through appropriate treatment—people
who suffer from depression in conjunction with chronic pain generally respond
fairly well to antidepressants—but such treatment is not always provided,
because of the misconception that anyone who is in constant pain must necessarily
Even worse, there was a
time, unfortunately not so long ago, when many people who complained of chronic
pain (see sidebar) were regarded as hypochondriacs or attention-seekers. Now we
know that these views were wrong, and that chronic pain is a genuine disease,
a distinct disorder of the nervous system, produced and maintained by a variety
of abnormal cellular processes.
pain comes in many different forms. It can recur intermittently, as in the case
of migraines, or it can be constant while varying in intensity, as in the case
of backache (see box below). But chronic pain caused by degenerative diseases
such as rheumatoid arthritis and cancer can not only be constant but also grow
continuously more intense as the disease progresses (see sidebar).
pain can also set in when an accident, an infection, or a surgical operation damages
a nerve so that it keeps sending out pain signals even though the the original
injury has otherwise healed completely. This type of pain that originates basically
in the nerve cells themselves is known as neuropathic
Back pain is certainly one of
the most common kinds of pain. In fact, it is the top reason that people visit
specialized pain clinics. The statistics on back pain are telling. About 80% of
all adults will experience back pain at some time in their lives. Back pain is
the leading cause of disability in adults under 45 years of age and the leading
cause of work absences lasting less than 15 days. Back injuries account for 25%
of all disability benefits paid out by insurance companies. Indeed, back pain
seems to be one of the most common ailments of our age.
Back pain can be
highly disabling, limiting people’s activities of daily life and generating
which is itself an aggravating factor in back pain. Given that each of us needs
to bend our back some 1 500 to 2 000 times per day, the importance of breaking
this vicious cycle as quickly as possible becomes readily apparent.
why are our backs so vulnerable in the first place? The first thing to remember
is that they are complex assemblies of bones, nerves, muscles, tendons, and ligaments,
all of which can produce pain. Second, from childhood on, all of us subject our
backs to various kinds of abuse—carrying too many books to school in our
backpacks, not getting enough exercise, enduring too much stress, performing exhausting,
repetitive physical work, and so on.
More specifically, the back is a framework
of bones—the spinal column—that surrounds and protects the spinal
cord. The spinal column consists of 24 vertebrae (7 cervical, 12 dorsal, and
5 lumbar) separated from each other by intervertebral disks that serve both as
joints and as damping cushions. This complex mechanism is our inheritance from
of the four-legged vertebrates who preceded us, yet we demand that it
do the hard work of maintaining our upright posture as bipeds.
some pieces of this puzzle can sometimes shift slightly out of place, thereby
causing back pain. Back pain can occur in each of the three major anatomical areas
into which the back is divided. Thus we speak of cervicalgia (pain in the neck
and upper back), dorsalgia (pain in the mid-back), and lumbalgia (pain in the
lower back, which is the commonest of the three).
can arise, for example, when you remain too long in an abnormal position, such
as leaning forward or sitting or lying down in a poor posture. This places an
overload on your ligaments, muscles, and disks. Another common source of back
pain is when you wrench your back or “throw it out of place” by making
an awkward movement, often one that involves twisting the torso.
not talking here about major displacements of the spinal column, such as can occur
in highway accidents and cause significant damage to the spinal cord. Instead
we are talking about cases where the shift in the position of the vertebrae is
very small but nevertheless reduces their mobility. Quite often, this lack of
mobility causes contraction
of the muscles nearby, thus further increasing the pain.
can also be damaged if you make repeated
movements in an awkward way, or carry loads that are too heavy
for you. Too much pressure on the spinal column can force part of a disk out beyond
its normal boundary, resulting in what is called a herniated disk. The herniated
disk may then in turn compress a nerve
root and produce referred pain in an arm or leg (see sidebar). Leg pain
caused by a pinched nerve root in the lumbar spine is known as sciatica. The vast
majority of herniated disks occur in the lower back, and they account for about
2% of all cases of back pain.
Some of the pathologies that cause back pain,
such as herniated disks and osteoarthritis, can be readily identified with x-rays.
But in the vast majority of cases, doctors cannot find any signs of what is causing
the back pain, even with x-rays and other diagnostic scans. What is more, in 90%
of all patients, these pain symptoms fade away on their own in less than a month
That said, if your back ever really starts to bother you, you are
best advised to go see a doctor, before the pain becomes chronic. Your doctor
can give you some simple rules to follow to prevent back pain: exercise regularly
to maintain good muscle tone in your back; when lifting anything heavy, bend at
the knees instead of with your back; avoid carrying anything too heavy; and avoid
any activities, such as jogging, that generate repeated jolts to the spinal column—instead,
engage in exercises such as swimming, which stretches your back muscles and tones
them at the same time.
You should also avoid sitting for too long at one
time. A review of 25 studies has shown that working at a computer does not cause
lower-back pain, if you sit in the proper position. But the frequency of lower-back
pain does seem to increase if you sit for a long time in a bad position or while
being subjected to vibrations. The risks of back pain are thus 5 times higher
among truck drivers and 9 times higher among helicopter pilots than among the
Pain is sometimes felt at a different place on
the body from the one where there is actually a problem. This phenomenon is referred
to as projected or referred pain.
One common example is when you bump your elbow, then feel a pins-and-needles
sensation in your ring finger and your pinky. The explanation is that you have
compressed the ulnar nerve, which passes through your elbow. This compression
generates a series of nerve impulses that go back up the the spinal cord and make
you feel as if the pain is in those fingers. The same phenomenon is at work when
irritation of the sciatic nerve at the level of the lumbar vertebrae makes you
feel pain in your legs. Likewise, an irritated or spasmed
muscle in your neck can give you a headache.
Another classic example
of referred pain is the pain that people feel in their left arm or shoulder when
they are having an attack of angina. In this case, the actual problem is in the
heart, which is not receiving enough blood, but the pain is experienced in another
part of the body, in addition to often being experienced directly on the left
side of the chest.
Other diseases of the internal organs can cause the
same kind of confusion. A pain in the bile duct, for example can be projected
into the back. Or a pain that originates in the kidneys, digestive tract, or vertebrae
can be projected to the testicles.
In many cases where the viscera (internal
organs) are the source of the referred pain, the explanation lies in what is known
as viscero-somatic convergence. The internal organs have very few dedicated pathways
for carrying pain signals up the spinal cord to the brain. Most of the nociceptive
pathways from the viscera converge
on the same medullar dorsal horn neurons that receive the nociceptive pathways
from the skin. The hidden cost of the body’s saving resources in this way
seems to be the confusion that can result as to the actual location of the pain.
Science is far from having solved all the mysteries
of the placebo effect. The mystery of “open placebos” is a good example:
researchers openly tell patients that they are being given a sugar pill three
times per day. Thus they are well aware that they are not taking any active medication,
yet they nevertheless report that their condition has improved!
phenomenon was observed back in the 1970s among heroin addicts, who had discovered
that when they couldn’t get any heroin,
they could ease their withdrawal
symptoms at least somewhat simply by injecting themselves with water. Researchers
observed that these individuals also displayed physiological signs, such as contracted
that were similar to their responses to opiates, thus showing that conditioned
responses are involved in the placebo effect.
Just as patients’ positive expectations
can improve their health (the placebo effect), their fears regarding a treatment
can make their health worse, even if the treatment actually involves no active
ingredient! This opposite side of the coin from the placebo effect is known as
the nocebo effect (from the Latin for “I will harm”).
Just like the placebo effect, the nocebo effect is not attributable to
any mental disorder, but simply to an aspect of the functioning of the normal
human brain. In a study conducted at the University of Turin in Italy in 2007,
two groups of men were taking a prostate medication. One group were told that
the medication’s possible side effects included erectile dysfunction and
loss of libido, while the other group were not. The number of men who then reported
experiencing these side effects was three times higher in the first group than
in the second.
Many other studies have confirmed that patients who have
been informed of the possible undesirable side effects of their treatment are
more likely to experience them than patients who have not been so informed. Put
another way, reading the description of possible side effects on a bottle of medicine
can make you sick. And just as the placebo effect is regarded as enhancing the
impact of a medication, the nocebo effect is regarded as potentially accounting
for a portion of the negative side effects of any active medication.
a study in the 1960s, when ethical constraints on scientific experiments were
less elaborate than they are today, subjects were given sugar water and told that
it would make them vomit. The result: 80% of the subjects did in fact vomit. In
another typical example of the nocebo effect, someone takes a medication knowing
that its side effects can include abdominal pains, and then begins to experience
such pains within the next few minutes, before his or her system has even had
time to absorb the active molecule in the medication!
Here is another well
known manifestation of the nocebo effect: anticipating pain increases its magnitude.
Experiments have shown that such apprehension caused an increase in brain levels
of cholecystokinin, a neuropeptide
that is known to facilitate the transmission of painful sensations. Furthermore,
when the subjects were injected with a cholecystokinin blocker, the painful nocebo
In another possible instance of the nocebo effect,
about one-quarter of patients who receive placebos in clinical trials complain
of side effects such as headaches or sleepiness. One possible explanation is that
these people simply become hypervigilant about minor discomforts that any healthy
person experiences occasionally.
Symptoms such as accelerated heart rate,
dry mouth, nausea, and diarrhea might also be explained by anxiety and apprehension
about the possible side effects of a treatment. These symptoms are classic
bodily responses to stress, and are studied as part of the broad research
field known as psychoneuro-immunology (see box to the right).
example of how people’s mental processes can influence their perceptions
and their physiology is the way that their expectations regarding medical treatments
can influence the outcome of those treatments. This is the famous “placebo
effect”, which can
provide people with relief even if they have not absorbed any pharmacologically
active ingredient. Simply believing that a medication or other treatment is
going to help can can produce very real organic changes that result in relief.
But the reverse is also true: in some cases, worrying about the possible effects
of a treatment can cause equally real negative symptoms. This is known as the
“nocebo effect” (see sidebar).
neuroscientists are beginning to identify the mechanisms
underlying the placebo effect, it varies greatly with the situation and the
individual concerned and hence depends on many factors that are not yet well understood.
These factors can, however, be classified into four main groups: the placebo
object itself, the doctor providing the treatment, the
patient, and the disease.
now know that the physical and chemical characteristics of the object
used as a placebo can greatly influence the size of
the placebo effect.
First, the mere name
given to the placebo object can influence its effectiveness. A placebo
presented to the patient as morphine will relieve pain more effectively than one
presented as aspirin.
Next, the physical
form of the placebo object has a major influence. One study has shown
that placebo capsules are more effective than placebo tablets, and other studies
have shown that placebo injections are more effective than placebo pills. The
size of the placebo effect thus seems to increase as the therapeutic intervention
becomes more invasive.
The effects of
a placebo can also be influenced by its price. Telling patients
that a placebo is a very expensive medication reinforces their belief in its potency
and increases its effectiveness.
dosage of a placebo and the number of times it must be
taken can also influence the placebo effect. For example, some authors
have found that when the dosage of a placebo was increased, the frequency of undesirable
side-effects (such as upset stomach, sleepiness, and dizziness) also increased,
if the placebo was administered for several days.
placebo effect can also interact synergistically with an actual
active medication. For example, in one study, one group of subjects was given
information that encouraged them to believe in the analgesic power of a placebo,
while another group was given information that encouraged them not to believe
in it. After both groups of subjects had taken the placebo, analgesia was observed
in the group that “believed” in the placebo, but none was observed
in the group that did not believe. When both groups were then given aspirin, greater
analgesia was observed in the group of “believers”. The practical
implication of this kind of synergy is that the placebo effect can allow the dosage
of actual analgesics to be reduced.
also generally take less time to begin having an effect than
active ingredients do. This is true in treating pain, but even more so in treating
depression, where placebos can begin to have an effect after one or two days,
whereas, in principle, antidepressants
can take two to three weeks before doing so.
amount of time required to reach peak activity level is about
the same for placebos as for real medications, and sometimes even shorter.
time that an analgesic placebo remains effective can be as much
as two weeks, after which the effect diminishes gradually. However, several cases
have been reported in which placebos remained effective for more than a year,
notably in the treatment of panic
doctor also plays a prominent role in the placebo effect. Some
authors believe that the
origins of the placebo effect lie in the asymmetry of the doctor/patient relationship.
The medical ritual, the protocols that it involves, the doctor’s
qualifications, and the length of the waiting list can all create a favourable
impression on patients and make them believe
that they will get better—the belief that is the basis for the placebo effect.
The amount of conviction
with which the doctor presents the medication to the patient, emphasizing, for
example, its power as a treatment, is an especially influential factor in the
The amount of warmth
that doctors show their patients is another very important factor for maximizing
the placebo effect. As is often stated quite rightly, medicine is not only a science,
but also the art of treating other human beings. In this regard, it is obviously
desirable for doctors to foster the non-specific
benefits of the placebo effect when seeing their patients.
example, in one study of patients who were given placebo acupuncture treatments
for irritable-bowel syndrome, the researchers compared the analgesic effectiveness
of “warm” acupuncture sessions, in which the therapist greeted the
patients warmly, listened to them attentively, and provided lots of explanations,
and “cold” acupuncture sessions, in which there were no verbal exchanges
between the therapist and the patients. In both cases, the needles were inserted
superficially and away from the meridians recognized by professional acupuncturists.
Compared with a control group that had received no treatment at all, the group
that received the “cold” placebo showed significant improvement, but
the group that received the “warm” placebo showed even more.
famous experiment was conducted by Dr. K.B. Thomas, a family physician in England.
Dr. Thomas selected 200 of his patients who were complaining of various pains
that he was actually unable to diagnose accurately. He gave half of these patients
a reassuring diagnosis and told them that they would get better very quickly.
With the other half, he remained vague, and suggested that they come back if their
pain persisted. Two weeks later, 64% of the patients in the first group had gotten
better, while only 39% of those in the second group had done so.
authors even go so far as to conclude that the mere fact of being in a therapeutic
relationship provides a placebo effect to varying degrees. This would be an example
of what some have called the
Hawthorne effect, in which subjects’ simply knowing that they are being
studied or listened to causes favourable changes in them. In the Hawthorne study,
the changes involved increased productivity among assembly-line workers, but they
can also involve improved health, as in the placebo effect.
third main set of factors on which the placebo effect depends involve the patient.
It is hard to identify any personality traits that would define a type of patient
who always responds to placebos. This probably indicates that an individual’s
response to placebos depends on many factors besides a simple personal predisposition.
That said, patients’ expectations
with regard to a given treatment have a great influence on the occurrence
of a placebo effect. These expectations are so important that if, for example,
a patient questions the effectiveness of a proposed operation that might alleviate
his or her chronic back pain, some doctors will try to avoid this surgery.
patient’s beliefs can also influence the effectiveness
of a particular placebo. In one study, for example, a group of subjects who believed
in supernatural beings responded better to the placebo effect of floral essences
if these essences were presented as being somehow associated with such beings
than if they were presented simply as medications produced by the pharmaceutical
industry. And the reverse was found to hold true for subjects who were more rationalist
Lastly, as regards the
fourth set of factors, the nature and intensity of the disease can
influence the placebo effect. Diseases that have a large psychosomatic
component have a greater chance of responding to the placebo effect,
as do diseases that cause intense suffering along with a great
desire to see it disappear. The placebo effect
is also more pronounced with disorders that have a large subjective
component, such as depression,
Researchers have two
main strategies that they can use to assess the effectiveness of a medication.
The first is to eliminate its specific effect by administering a tablet that is
presented as the medication but does not contain its active ingredient (in other
words, to administer a placebo). The second strategy is to eliminate its non-specific
effect, by hiding the administration of the active ingredient from the patients.
clinical trials, in which the placebo effect creates observable improvements
in patients who have unknowingly received a placebo, this second approach, the
hidden administration of the active ingredient,
works in roughly the opposite way. For example, if patients are already receiving
an intravenous drip, they can easily be given an antipain medication without their
knowing, and then asked to complete a questionnaire evaluating their subjective
perception of their pain level. Next, they can be given exactly the same dose
of the same medication openly (meaning that the doctor uses a syringe to inject
the medication and explains its nature and expected effects to them), and then
asked to complete the questionnaire again. If they report less pain this time,
this indicates a non-specific component that is probably attributable to the placebo
Such studies show that analgesic effects are far smaller with hidden
administration, both of active medications and of placebos. For example, if a
patient is told that he is going to be given an intravenous injection of a powerful
analgesic that will ease his pain, and then a tourniquet is applied to his arm
and he is injected with normal saline solution instead, he will experience pain
relief. But that will not happen if he is already hooked up to an intravenous
drip and is injected with the same dose of normal saline solution without being
aware of it.
Another experiment has shown that
the dose of analgesic needed to reduce pain by half was far higher with hidden
administration, and that this held true for all four analgesics that were tested.
The same trend was observed in the time lag before the analgesic effect set in:
it took longer with hidden administration.
Experiments with open and hidden
cessation of treatment with morphine
confirmed these results: the pain returned more quickly and was more intense when
the patients were told that their treatment was going to be halted than when it
was halted without their knowing. This phenomenon can also come into play in the
nocebo effect (see sidebar): in this case, the fear of the pain’s returning
can aggravate the pain.
Exactly the same results were obtained in comparing open and hidden
administration of the anxiolytic
diazepam to patients who were experiencing major anxiety
following an operation, as well as in comparing the open and hidden withdrawal
of this treatment.
There are thus ways to study the placebo effect without
even having to administer a placebo pill. A corollary is that a placebo pill delivered
in such a way that the patient does not know about it will never have any effect
on that patient. This is entirely understandable, because without a prior explanation
of the treatment, the patient is in no position to build up any expectations about
it. This is another reminder of the importance of the doctor-patient relationship
among all the factors that contribute to the placebo effect.
The placebo effect is a special case of the brain’s
more general ability to exert a profound influence on the functioning of the body.
The discipline that examines this influence is called psychoneuro-immunology
and developed out of research done by U.S. psychologist Robert Ader starting in
Ader fed laboratory rats a combination of sweetened water
and an immunosuppressive drug and successfully conditioned them to associate the
drug’s effects with the sweetened water, so that subsequently, just feeding
them the sweetened water alone sufficed to lower their immune defences. This was
the first scientific evidence that the nervous system can influence the immune
Since then, numerous experiments have confirmed that the two major
adaptive systems of the human body—the brain and the immune system—are
in constant communication with each other. They communicate through two main neural
pathways: the hypothalamic-pituitary-adrenal
axis and the sympathetic
nervous system, as had previously been surmised by forerunners of psychoneuroimmunology
such as Hans Selye and Henri
It is interesting to consider the scientific view of the placebo
effect in light of the evolution of this discipline. Before the 1970s, the potentially
harmful effects of stress on health were still regarded as a fairly esoteric topic.
Nowadays, psychoneuroimmunology is a very active research field, and no one in
the scientific community any longer questions these interactions between mind
and body. As a result, many researchers believe, the placebo effect is now
reaching just about the same level of general acceptance.
Studies on the
placebo effect are now providing increasing evidence that it involves cascades
of biochemical reactions including, for example, the secretion
of endorphins that can alleviate pain. Other forms of healing associated with
the placebo effect might be due to a more general positive impact of expectations
that help the immune system to function more effectively. Conversely, it has also
been frequently confirmed that severe chronic stress can weaken the body’s
immune functions and make it more vulnerable to a variety of pathologies, including
cardiovascular disease and depression.
Thus, a healthy immune system routinely eliminates the precancerous cells and
viruses that are always present in the human body, while a depressed immune system
allows them to proliferate.
This does not mean that, to oversimplify grossly,
you can cure a cancer with a smile. But perhaps you can prevent some cancers by
avoiding weakening your immune system. And as we now know, the thoughts and expectations
generated by our brains can affect the neurochemistry of the complex mechanisms
that keep us healthy.