The potential toxicity of psychoactive substances, like that of any medication, depends on the amount consumed. This toxicity of course varies from one drug to another, but as a general rule, the higher the dosage you consume, the more the substance will have toxic effects on your organism.
An estimated 1.5 million Canadians now smoke marijuana occasionally, for pleasure. This recreational use does not cause any escalation in the great majority of cases.
DRUG CONSUMPTION
The human brain contains circuits that provide us with pleasure to
reinforce behaviours that are helpful to our survival. The brain
thus naturally favours those behaviours that lead us to seek euphoria. One
direct way of achieving euphoria is to take psychoactive substances.
The risks associated with consuming a drug of course vary with
such factors as the nature of the drug, the vulnerability of
the person consuming it, and the amount consumed. But the main
determinant of a drug’s long-term impact
on the brain is whether it is taken for a short time or a long
time. There are three categories of drug use: recreational
use, abuse, and dependency. (Roll your cursor over the three
traffic lights to read descriptions of each category).
But
vulnerability to dependencies is not limited to psychoactive
substances. People can also become dependent on compulsive behaviours,
such as compulsive gambling or bulimia, which can also lead to
an irresistible need to continually repeat the behaviour in question.
The nicotine
in tobacco is a very good example of a substance
that causes physical dependency. According to surveys,
about half of all smokers would like to quit. About
25% give it a serious try every year. But in the end,
only one out of 2 (12% of all smokers) actually manage
to do it. In other words, not many, which clearly proves
that this is not just a question of will power. While
it is true that the nicotine in cigarettes can aid
in concentration, act as a tranquilizer, and regulate
appetite by binding to sites in many different parts
of the brain, it also binds to sites in the reward
circuits of the limbic system and thus creates a dependency.
Nervousness and irritability are two sensations commonly
experienced when the smoker’s brain no longer receives
its accustomed dose of nicotine. For over 30 years, the tobacco
companies have vehemently denied any dependency associated
with their product. Even today, they use all kinds of deceptions
to lure younger people into the vicious circle of dependency.
Children must be warned about the risks of tobacco between
the ages of eight and ten. By age 12, it is already too late.
The famous methadone programs for
heroin addicts let them reduce the suffering of heroin
withdrawal, one of the most painful kinds there is. Methadone
is a molecule that resembles heroin and
binds to the same receptors. But it does not produce the
rush of pleasure that heroin does. Similarly, the physical
symptoms associated with methadone withdrawal are less
severe than those associated with heroin withdrawal. This
is why heroin addicts prefer to withdraw from methadone.
Denial and rationalization are
two psychological defence mechanisms commonly used by people
with drug dependencies.
DRUG DEPENDENCY
The
behavioural changes that accompany the compulsive consumption
of a drug can be better understood if we distinguish between
physical and psychological dependency.
Physical
dependency is the organism’s physiological
reaction to the absence of the drug. It is a state of deprivation
that is accompanied by uncomfortable physical symptoms known
as withdrawal (see box below).
Physical dependency occurs when the body is deprived of drugs
such as opiates (opium
derivatives), tobacco, alcohol,
and certain psychoactive
medications. This deprivation leads to physical symptoms
that vary with the drug: pain, in the case of opiates; severe
tremors, in the case of alcohol; and convulsions, in the case
of barbiturates and benzodiazepines.
In fact, most symptoms of withdrawal from a drug are the opposite
of those observed when a person is intoxicated with that same
drug. The reason is that the brain has developed compensatory
pathways, and when the drug is taken away, they are suddenly
overcompensating. These symptoms can also be accompanied by
behavioural problems, such as anxiety,
anguish, irritability, and agitation.
In the case of certain psychotropics, it can be very dangerous,
or even fatal, for someone to suddenly stop taking them if
he or she has been consuming them regularly. Thus, people withdrawing
from anxiety or sleep medications should do so under the supervision
of a qualified person.
Psychological
dependency can last far longer than physical dependency:
years, or even a lifetime. It is based more on the individual’s
traits (habits, affective states, lifestyle) than on the
substance itself. It is the memory of the pleasure associated
with the object of the dependency that the individual thinks
about often and longingly.
Sometimes, the re-emergence of a problem that the person
was trying to suppress by taking the drug can cause them
to recidivate (start taking it again). People may also
remain dependent out of fear of the painful withdrawal
that awaits them if they stop taking the drug.
Psychological dependency is often described by the word " craving ",
which clearly conveys the intense desire to take the drug
and feel its effects. Craving is similar to the physiological
sensations of hunger and thirst.
Another psychological factor
encouraging drug dependency is the conditioned
learning that occurs unconsciously
when someone is taking a drug. In this
process, both endogenous and environmental
stimuli become associated with the desired
substance and acquire the power to activate
the craving all on their own. For people
addicted to injectable drugs, the whole
environment surrounding “shooting
up” (syringes, “shooting
galleries”, etc.) therefore becomes
tremendously important.
Simply coming into contact with this environment can cause
them to start taking the drug regularly again.
So can taking just a small amount of the drug, or being
under stress, or even experiencing subjective emotions
formerly associated with taking the drug.
Cocaine and amphetamines are
good examples of substances that do not
cause any physical dependency, but do
cause very intense psychological dependency.
Neurobiochemical studies have shown the reward
circuit to be an important substrate of psychological
dependency. That said, many
theoretical attempts to explain the mechanisms of dependency
are still being debated today.
Successfully bringing a drug-dependent
person through withdrawal is no easy thing. The reason is
that repeated consumption of a drug short-circuits
normal neurotransmission in the reward circuit.
The brains of drug-dependent people adapt to the regular
introduction of psychoactive substances from external sources
by modifying their production of certain neurotransmitters.
The withdrawal syndrome occurs when this external input suddenly
ceases. The organism, which has deactivated certain of its
metabolic pathways, will then take a certain amount of time
before it re-establishes the equilibrium of its neurotransmitters.
There are then two solutions for eliminating the discomfort
of withdrawal: take the drug again and allow the dependency
to become even more firmly established, or give the organism
the time it needs (from a few days to a few weeks) to re-establish
the equilibrium of the neurotransmitters in its brain and thus
the chance to escape from the vicious circle of dependency.
To continue getting the same sensation
of giddiness and euphoria, drug-dependant people often have
to keep increasing their dosage. In other words, they need
more and more of the drug to get the same effect. This well
known phenomenon is known as drug tolerance,
or habituation.
Tolerance represents an adaptation at the cellular level. The
brain’s neurons will, for example, modify the number
or sensitivity of their receptors to adapt to the increased
dosage. To experience a pleasurable sensation, the drug-dependent
person will therefore have to go beyond this new threshold.
This means increasing the dose a bit more, and so on. Tolerance
can also be induced elsewhere in the organism. For example,
when people drink, their livers activate enzymes that convert
alcohol into less harmful substances. This is why they develop
a tolerance that forces them to drink considerable amounts
of alcohol just to get a little bit drunk.
Though tolerance is regarded as one of the characteristics
of drug addiction, it is neither a necessary nor a sufficient
condition to trigger a dependency. Some non-psychoactive substances,
such as certain hypertension medications, can also induce tolerance.
Conversely, there are certain psychoactive drugs, such as amphetamines,
for which no tolerance effects are observed.
