About 60% of all Americans
have tried illegal drugs. Even when you exclude marijuana,
the figure is still close to 30%. And if you include alcohol,
a substance that is legal but that can create a dependency,
the figure rises to 90%. Very few of these people are actually
going to develop a dependency.
Even with a drug such as cocaine,
which is highly conducive to dependencies, only 15 to 16%
of the people who try it become dependent on it within the
10 years following the first time they take it.
It is interesting to compare
the general attitude of one teenager who has low self-esteem
and a fear of facing up to problems with another teen who is
more confident and feels that he or she can cope with problems
as they arise. These two teens will react very differently
to the problems of everyday life. The psychologically healthy
teen will try to take action to deal with them, while the teen
whose behaviour is more inhibited will instead try to escape,
often by using psychotropic drugs. Taking these drugs will
temporarily suppress this teen’s sense of anguish, but
increase his or her sense of failure at being unable to solve
The origins and causes of the various
forms of drug addiction are still being debated within the scientific
community. In some individuals, such as alcoholics, genetic predispositions
may come into play.
But the consensus is that for most people, abusing psychoactive
substances is a learned behaviour designed to cope with some form
of distress. Some people use drugs to suppress disagreeable experiences
(for example, drowning their sorrows in alcohol after a quarrel
with a spouse). Others use drugs to enhance agreeable sensations
(such as the feeling of disinhibition that drinking alcohol can
Hence, it is the meanings that individuals ascribe to their behaviours
that may pose a problem.It is the difference between the experience
that an adult might have while sharing a joint in the evening with
some friends, and the experience that a teenager might have while
smoking the same amount of pot in secret to forget his or her problems.
Escalating consumption of a street drug or a medication is therefore
the result of a process and attitudes that depend on factors in
the particular individual’s personality, motivations, and
life experience, as well as in his or her family setting and social
environment. (To learn more about each set of factors, place your
cursor over each part of the diagram below.)
The presence of a relatively
large number of these contributing factors should set off an
alarm about that individual’s risk of dependency on
The term ‘’sensitization’’ refers
to an increase in the effect of a drug when it is used repeatedly.
Sensitization is thus the opposite of tolerance. Sensitization
may also occur because the underlying biological systems
adapt in different ways to repeated exposure to a drug. The
two kinds of drug effects that are generally subject to sensitization
are psychomotor effects and reward effects. Since both types
of effects involve the reward circuit, it is thought to be
this neural system that undergoes the changes involved in
Someone may use several substances regularly (for instance,
tobacco, alcohol and anxiolytics several times per week) or
several substances all at once (for instance cannabis, alcohol,
and tobacco all in the same evening).
Both types of behaviour are called “polyconsumption”.
The effects of drugs can be amplified in such cases, leading
to more serious health risks. Polyconsumption can also lead
to polyaddiction, meaning dependency on several drugs.
Over the years, various
theories have been offered as to how the changes in brain
and behaviour associated with drug-taking can lead to dependency.
For proponents of this theory, dependency develops through positive
reinforcement: people take drugs to try to repeat a pleasant
experience. This theory was formulated in the mid-1980s on
the basis of self-stimulation experiments conducted in the
1950s. But this view of drug addiction as a form of self-medication,
in which individuals choose a given substance according to
their particular needs and the particular effect they are
seeking, has shown its limitations in other experiments over
For other theorists, the main cause of drug addiction is
the desire to alleviate the suffering that addicts experience
when their drug is withdrawn. This theory of negative
reinforcement was proposed as early as 1948. But it too
fails to explain certain phenomena adequately, in particular
the fact that drug addiction practically never develops when
opiates are prescribed for somatic pain, if the prescription
is written properly.
Solomon and Corbit’s opponent process theory (Solomon
and Corbit 1973, Solomon 1977) offers an elegant explanation
of drug addiction, combining the search for euphoria with
the avoidance of withdrawal pain. Other authors have viewed
drug dependency mainly as a learning aberration–specifically,
the development of very strong habits of stimulus-response.
This theory is based on the discovery that the reward
circuit appears to be involved in learning, and particularly
in recording memories of the environmental markers associated
with rewards. This explanation is helpful for understanding
of the environment on dependencies, but also has its
limitations, with regard to both explicit and implicit
approach begins with the observation that the mere presence
of a reward, even one that is inaccessible, can cause the
dopaminergic neurons in an animal’s brain to start
secreting more dopamine. Simultaneously, the animal displays
approach behaviour toward the reward in question. Some
researchers believe these observations indicate that drug-seeking
behaviour should be disassociated from the satisfaction
that drugs provide. In this view, drug addicts have an
exacerbated desire for their drug of choice, and the pleasure
that it provides them becomes secondary. This theory even
proposes that dopamine
drives only the drug-seeking activity, while the experience
of pleasure is triggered by other neural pathways.
In 1993, Robinson and Berridge suggested that a state of
hyperexcitability (sensitization) of the mesolimbic dopaminergic
system might be the source of the cravings that drug addicts
experience. According to this theory, the dopaminergic system
attributes a value, or “salience”, to stimuli
associated with its activation, thus making them attractive
or desirable “incentives”.
Still another theory holds that drug-dependent people suffer
from a dysfunction of the systems of the frontal cortex that
normally regulate decision-making and impose inhibitory controls
on behaviour. This dysfunction would result in altered judgment
One last hypothesis focuses on the idea that individuals’
attitudes toward drugs depend fundamentally on whether
the baseline activity of the dopaminergic neurons in
their brains is above or below a certain level. If it
is above this level, the individual experiences satisfaction.
If it is below, the individual experiences a craving.
There is an interesting analogy here with theories that
individuals perceive and assess the intensity of pain
by comparing it with subtler but related sensations experienced
drug-addiction-research institutes, such as the National Institute
on Drug Abuse (NIDA) in the United States, regard drug addiction
as a disease of the brain that may eventually be treated by
various pharmacological methods. This approach is certainly
more progressive than those that treat addicts as delinquents
who must be punished.
But the phenomenon of drug addiction is far broader than its
neurobiological corollaries alone. Even just to define it, its
psychological and social dimensions must also be considered.
For example, the problem with methadone treatments for heroin
addicts lies not so much in the pharmacology of methadone as
in the fact that patients perceive the system that provides these
treatments as rigid, controlling, and oppressive. Drug addicts’ social
isolation also makes it hard to reach them, earn their trust,
and ultimately, offer them pharmacotherapy.