OUR POSITION FOR A CANADIAN PUBLIC POLICY
REPORT OF THE SENATE SPECIAL COMMITTEE ON ILLEGAL DRUGS
VOLUME I : PARTS I and II
Effects and Consequences
as we saw in Chapter 5, acts on the central and peripheral nervous systems in
various ways. While research has established a fairly clear role for some of
the components of cannabis, D9THC
in particular, the main active component, we are less sure of the role of
other chemicals. Similarly research, which is often conducted on laboratory
animals or in an even more specialized manner on molecules extracted for
experimental purposes, does not reflect the conditions under which the average
user uses marijuana. We have seen that, in some cases, dosages used for
experimental purposes on laboratory animals, in particular to determine the
chronic effects of regular use, are dosages that are unimaginable for humans,
the equivalent of 570 marijuana cigarettes a day. Since THC content varies
greatly with the cannabis available on the market, since users make different
use of the drug depending on the place and circumstance, and since individual
characteristics interact with the actual effects of cannabis, knowledge of the
effects is necessarily influenced.
From an even more
technical standpoint, we should point out that a statistical association –
that is, the fact that two facts are concomitant – in no way indicates
causality. To infer causality, a certain number of methodological
prerequisites must be satisfied. In addition to the statistical association,
we must be able to dismiss chance and alternative hypotheses, and show that
the causative factor does precede the inferred consequence. According to the
inferences can be drawn from research findings by judging the extent to which
the evidence meets widely accepted criteria. These include: strength of
association, consistency of association, specificity, dose-response,
biological plausibility, and coherence with other knowledge. These criteria
are not sufficient to show that an association is causal but the more are met,
the more likely it is that the association is
Moreover, a strong
tradition in the philosophy of science holds that you can never prove a
hypothesis. The most you can do is falsify – that is, dismiss –
To try to
meet the requirements of causality, researchers have developed sophisticated
research methods, providing in particular for the random selection of subjects
for a study, the random assignment to experimental conditions and
non‑experimental conditions (control group), the use of double blind and
placebo techniques, the careful control of intervening variables that could
represent as many alternative hypotheses as researchers are trying to
eliminate. This is how, for example, they usually try to test medications that
are put on the market.
For most questions
involving human behaviour, a fortiori
in society, it is difficult and rarely possible to establish such a causality
relationship for the simple reason that each of these methodological
requirements can rarely be met. In our case, the effects of cannabis use, the
methodological constraints are particularly obvious. We cannot gather a random
sample of cannabis users since we don’t know the population. Therefore we
must rely on alternative methods for selecting subjects (volunteers, for
example). It is difficult to have people smoke cannabis who would otherwise
never use it38
without running the risk of contravening certain rules of ethics, or even
legal provisions. And if we resort to people who have already smoked it, there
is necessarily contamination of the control group. The cannabis that is used
in the lab may be completely different from that of users who buy it off the
street. And controlled laboratory conditions definitely do not reproduce the
methods of cannabis use, which we know are usually a form of social ritual. As
for studies–and they are numerous–conducted on animals (monkeys, mice,
rats…), they may be interesting, but the possibility of transposing their
results onto humans is limited. Lastly, we note that, as most cannabis smokers
also smoke tobacco and drink alcohol, it is difficult to separate the effects
of one from the effects of the others.
Obviously that does
not prevent researchers from conducting studies, and these studies are also
necessary. However, it does require researchers to be as prudent as possible
when interpreting their results, in particular with respect to the ability to
generalize about all marijuana users and to draw causal inferences. This is a
caution that we do not always find, far from it, as this chapter will
Lastly, we should
note the distinction between effects and consequences. Smoking cannabis has
immediate effects, some physiological and some psychosocial, that we must
describe. But smoking cannabis, especially repeatedly, can also have
consequences, some immediate – for example, the ability to perform certain
tasks or the ability to drive a vehicle – and others more distant – for
example if smoking cannabis results in a greater risk of lung cancer and if it
has a lasting effect on memory.
We are aware of
just how arbitrary these distinctions can be insofar as a human being is a
whole, an organism integrated into his emotional and social environment and
into his ecosystem. The physiological, psychological and social effects
interact with one another, infiltrate one another, influence one another and
act together rather than separately. In some ways, these distinctions remain
the reflection of our incompetence, or at least of our inability, to think
about the various systems of a human being as a whole, from every angle. This
same incompetence can, also in part, explain the difficulty we have in
creating a drug policy. It is to be hoped that those who come after us will be
able to develop an integrated, holistic approach. For now, we are forced to
use the means at our disposal, our fragmented understanding.
preliminary note. We were constantly guided by the need to be rigorous. Be
that as it may, our resources did not enable us to be completely thorough and
to examine the studies one by one for all these questions. In total, we know
that approximately ten thousand studies have been published on cannabis over
the last forty years! However, as Nelson points out, “Although the total volume of this literature is somewhat daunting at
first glance, a sampling of the material soon reveals that much is repetitive
and a relatively small number of papers are continually referred to by most
Despite this repetition, we could not go without examining a certain number of
these studies. That is why we commissioned the preparation of a summary report
and also examined the summaries of scientific literature that were prepared in
chapter is divided into five sections. The first is a collection of statements
on the presumed effects of marijuana that the Committee heard or that it was
made aware of through its research. The following three sections examine the
acute effects of cannabis, followed in turn by the physiological and
neurological consequences, the psychological consequences and the social
consequences. Then, because of its significance and the central place it holds
in social and political concerns, we turn our attention specifically to the
question of dependence possibly arising from prolonged use of cannabis.
hearings, many witnesses told us what they knew about the effects of cannabis.
Some of this knowledge came from their own research work. Other knowledge came
from their professional experiences. And lastly, other knowledge was either
their interpretation of scientific literature or anecdotes. In this section,
we will not make distinctions between the testimony and we will not evaluate
its validity. We only want to highlight the richness, as well as the
complexity, of what we were told.
number one is that drugs, including cannabis, are harmful. (…) There is
considerable misinformation about the physiological consequences of cannabis
use. There is no doubt that heavy use has negative health consequences. The
most important are in the following areas: respiratory damage, physical
coordination, pregnancy and postnatal development, memory and cognition, and
psychiatric effects. (...) 
marijuana (cannabis) and its derivative products are described in this context
to distance the drug from the recognized harm associated with other illegal
drugs. This has been a successful yet dangerous approach and contributes to
the misinformation, misunderstanding and increasing tolerance associated with
marijuana use. Marijuana is a powerful drug with a variety of effects.
Marijuana users are subject to a variety of adverse health consequences that
include respiratory damage, impaired physical coordination, problem pregnancy
and postnatal deficits, impaired memory and cognition, and psychiatric
effects. Marijuana use is associated with poor work and school performance and
learning problems for younger users. Marijuana is internationally recognized
as a gateway drug for other drug use. Risk factors for marijuana dependence
are similar to those of other forms of drug abuse. (…) It was the consensus
of the international community to put marijuana and other substances under
international control. That decision was based on evidence of its harmfulness
to human health and its dependence potential. 
I wish to
briefly review two of what I believe are fairly well-established, harmful
effects of marijuana, and a number of other areas where there is considerable
contention. (…) By far the most consistent and clear-cut effect of marijuana
is disruption of short-term memory. Short-term memory is usually described as
"working" memory. It refers to the system in the brain that is
responsible for short-term maintenance of information needed for the
performance of complex tasks that demand planning, comprehension and
reasoning. The relatively severe impairment of working memory may help to
explain why, during the marijuana high, subjects have difficulty maintaining a
coherent train of thought or conversation. (…) Obviously this is relevant if
you are going to school stoned. (…) It is becoming increasingly clear that
cannabis is a drug on which regular users become dependent, and that this
adversely affects large numbers of people. 
has been shown to be associated with reckless drivers and motor vehicle
accidents. Evidence suggests that marijuana may contribute to an appreciable
number of traffic deaths and injuries in Canada. It has been shown to
negatively affect the academic and social development of some adolescents.
Marijuana can cause emotional and medical problems. Chronic use may be
associated with lung diseases such as bronchitis, emphysema and cancer. A
psychosis may develop in some individuals while other psychiatric symptoms
such as anxiety, low mood, depression and panic do occur. Marijuana is known
to be addictive. Although the rate of addiction varies, it is between 5 per
cent and 10 per cent. I should like to stress that addiction is a disease and
marijuana has the potential to be addictive to a genetically predisposed group
of individuals. 
evidence was that 95 per cent of the marijuana users in Canada are low,
occasional, moderate users. Their consumption of marijuana does not impact on
their health as long as they are healthy adults. The other 5 per cent are
chronic users, people who smoke one or more marijuana cigarettes per day. If
they continue to do that, they will ultimately get chronic bronchitis from the
smoking process. The same would be true if they were to roll up the grass off
their lawns and smoke that. They would inhale heated material over their large
airways and cause damage to them. There were three primary vulnerable groups:
pregnant women, which we submit is something between the woman and her doctor;
the mentally ill, particularly paranoid schizophrenics (…) then, most
importantly, immature youth. Young people who become involved with marijuana -
particularly on a regular basis - seem to suffer from a disruption of their
studies and the maturation process. As is the case with most intoxicants, it
is recommended that they not become involved with them until they have
I have one
resource from the Center for Substance Abuse Prevention in the U.S., where
recent marijuana research and a number of studies indicate some of the risks.
We already know and accept that cannabis has negative effects on many systems
- respiratory, motor skills, memory and immune - and that it creates drug
dependency and tension. In addition, we now know from numerous research
studies that there is a definite and acute withdrawal syndrome associated with
chronic cannabis use. (…) There is research that suggests there are effects
on the developing fetus. (…) I will speak to visual scanning, specifically,
attention dysfunction in the form of impaired visual scanning and related
functioning. Visual scanning develops particularly in early adolescence, so
earlier onset is associated with some concerns there. 
a number of negative health effects that have been created in the lab or have
been observed with long-term users (…). There are, of course, health risks
and negative health consequences with using the substance, but the majority of
those risks only occur under specific circumstances. The majority of the risks
are associated with long-term persistent and frequent use, and therefore must
be understood as such. There is at this point agreement that the so-called
dependence or withdrawal symptom may arise with heavy chronic users, but it is
very much limited to that small population. (…) a seminal report by Hall and
colleagues from Australia (…) concluded that the major risks of cannabis use
can be significantly reduced by avoiding driving under the influence, by
avoiding chronic and daily use, and by avoiding deep inhalation. These were
the key factors that allowed us to avoid many of the major harms and risks
associated with it. 
event, we are talking about plant derivatives that contain a number of
psychoactive alkaloids. The psychoactive effects are predominantly of mild
euphoria and time distortion, though disorientation and panic attacks may
occur. The appreciation of music, art and food are said to be enhanced, as is
appetite, and this later function seems important for one of the claimed
medical benefits in offsetting the effects of the chronic wasting syndrome in
AIDS and the prolonged nausea that accompanies chemotherapy. (…) Because the
drug is usually smoked, it has acute and chronic effects that are shared with
tobacco. These include airway irritation, cough, and probably with chronic
use, bronchitis, chronic obstructive pulmonary disease, and lung and
pharyngeal cancers. Its impact on the immune system is generally to impair the
function of the immune system, but the impact on human health of this
impairment is probably minor. (…) The effects of cannabis consumption on
reproductive health are negative in animal studies. (…) This obviously has
some relevance to human health. However, human studies have yet to show any
measurable adverse impact beyond some evidence of adverse behavioural and
developmental impacts on the children of mothers who smoked cannabis heavily
during pregnancy. (…) The impact of cannabis on cognition is well
documented. Short-term memory is adversely affected and chronic use may lead
to chronic measurable defects in cognitive functioning. However, this may be
more the result of persistent chronic intoxication than impairment in the
substance and the working of the brain. Psychomotor skills are adversely
affected by cannabis use. Driving or operating heavy machinery when
intoxicated is contraindicated. Again, in contradistinction to alcohol,
cannabis intoxication tends to slow drivers down rather than increase their
speeds. Similarly, cannabis smokers tend not to be involved in acts of
physical violence and aggression, and violence and aggression when intoxicated
is reportedly very rare. Cannabis use may provoke schizophrenic symptoms in
those with active schizophrenia or schizophrenic tendencies. Panic attacks and
dysphoria are also mentioned in the literature. There is an amotivational
syndrome described in the literature and cannabis is said to induce it, but
most researchers have discredited that over the last decade. (…) Concerns
have legitimately been raised about the effects of cannabis consumption on
adolescent development. As use tends to peak in late adolescence, this is an
important consideration. The adverse effects that have been noted include an
association with risk of discontinuation of high school, job instability and
progression to the use of harder drugs. The degree to which these associations
are causal is very controversial. Alternative hypotheses are that cannabis
use, like adolescent alcohol use, early onset of sexual activity, and tobacco
smoking, are in fact markers for other risks of adverse social conditions
(…) All researchers agree, however, that intoxication interferes with
academic prowess. Recent studies seem to demonstrate measurable though
reversible drops in IQ associated with heavy, persistent cannabis use and that
engagement in illicit activities carries substantial risks, especially perhaps
for youth whose connections to the school community are tenuous at best. 
like to first focus on the acute effects and then on the chronic effects.
"Acute effects" are those effects that you experience during the
course of action of a single dose. In the nervous system that includes a
period of several hours in which (…) you become "chemically
stupid." Side effects include decreased arousal and drowsiness, which
acts together with the drowsiness produced by alcohol and other central
nervous system depressants. Other side effects are impaired short-term memory,
slowed reactions, less accuracy in test performance and less selectivity of
attention. (…) Low doses generally produce the effects that cause people to
like smoking pot. They include mild euphoria, relaxation, increased
sociability and a non-specific decrease in anxiety. However, high doses
produce a bad mood, anxiety and depression. There can be increased anxiety to
the point of panic or even an acute toxic psychosis which, fortunately, is of
very short duration and goes away when the drug effect wears off. High doses
cause impaired motor coordination, unsteadiness of control and decreased
muscle tone, which is therapeutically useful. (…) With low doses, perception
is enhanced. That is part of the pleasure. In high doses, the same action
produces sensory distortion, hallucinations and the acute toxic psychosis to
which I have already referred. (…) It does not seriously affect the
cardiovascular system. (…) As to chronic effects, in the central nervous
system there is impaired memory, vagueness of thought, decreased verbal
fluency, and learning deficits in chronic, heavy users. I emphasize
"heavy" because the social user does not, by and large, show any
significant health effects. Neither does the social user of alcohol. (…)
These effects on cognitive functions fortunately tend to go away if the heavy
user stops, for whatever reason. As long as use continues, there is a chronic
intoxication, apathy, confusion, muddled thinking, depression, and sometimes
paranoia. (…) Cannabis dependence, as defined in the conventional diagnostic
criteria for dependence as set out in the latest edition of the American
Psychiatric Association, or the equivalent publication of the World Health
Organization, has been well documented in regular, heavy users. Numerous
studies now show that a significant percentage of regular users are dependent.
In some studies in Australia of long-term heavy users, mainly daily users for
periods of 15, 17, 20 years, 60 per cent or more of them met the diagnostic
criteria (…). Tolerance has been shown. By and large, it is not a terribly
serious effect, and the physical withdrawal syndrome is not severe.
Nevertheless, it is there, which indicates that physical dependence, in
addition to psychological dependence, occurs as well. 
long-term chronic effects of cannabis essentially cause the following
symptoms: memory loss, faulty attention and concentration, a slow-motivation
syndrome of passivity and low initiative, increased risk of respiratory
disease, more specifically asthma, bronchitis and emphysema and a higher risk
of cancer. (…) There may be hormone problems causing low fertility in men
and women. In men, this can cause the development of breasts which is very
unesthetic (…). Finally, in the long-term, it can also cause lower
resistance to infectious disease. 
we can see, opinions sometimes agree and often differ. They agree at least on
the nature of the consequences that may be of concern. One by one, we have
seen effects that were physiological (risks of cancer, effects on reproduction
and the immune system, deterioration of brain cells), effects that were
psychological (amotivational syndrome, risks of psychosis, impaired cognitive
function and memory in particular), and effects that were social (affecting
the family and work, as well as the ability to drive vehicles and operate
machinery). Opinions differ primarily on the scope of the conclusions that can
be drawn from this knowledge. To what extent, in fact, can we generalize about
the effects we observe in often small and rarely random samples of subjects?
Also, to what extent can we generalize about the data on chronic users who
represent – as we saw in the previous chapter – only a small percentage of
cannabis users? And especially, to what extent does this data allow us to
establish causal relationships?
The Committee also
finds that most witnesses stressed the negative aspects and rarely the
positive. However, if people use drugs in general, and cannabis in particular,
surely it isn’t just to destroy themselves or because these drugs have only
negative effects. Given the limitations of making any comparison between
substances, we can still draw a parallel with alcohol: most of us know the
pleasure of sharing a glass of wine with friends over a good meal, just as we
also know the dangers of alcohol abuse and alcoholism. The Committee also
notes that it is difficult, even for the most experienced researchers, to sift
through the knowledge without assigning it a valence relative to the direction
public policy should take. The same knowledge may be interpreted negatively
here and more moderately there, based on the interpreter’s preconceptions of
the “best” choice for public policy. We are not immune to this bias.
Moreover, we do not deny that we had preconceptions, derived from our personal
histories, our reading, and the hearings we held in 1996 to review Canada’s
drug legislation. Among these preconceptions, which oriented our reading of
the testimony, at least at first, we note:
The conviction that the
current system does not achieve its objectives, if only because of the
increase in cannabis use, by young people in particular;
A preference for an
approach that is more consensual and more in keeping with Canadian attitudes;
A preference for a
harm-reduction approach as indicated by the wording of our first mandate;
A tendency to distinguish
between soft drugs – including cannabis – and hard drugs (heroin,
A certain lack of
knowledge about the specific effects of cannabis, from the standpoint of the
toxicological and pharmacological studies conducted in recent years.
This being said, we
did not work in isolation. Not only were we accompanied by our research team
– sociologists, lawyers, criminologists – throughout our work, not only
were we also under the close surveillance of the witnesses in a way and of the
public in a larger sense, but primarily, other committees, in other countries,
have conducted similar reviews in recent years. Their work was a source of
inspiration and knowledge and as well a benchmark against which to compare our
acute effects are those that are produced immediately after use and while the
psychoactive effects are being experienced. These effects also correspond to
what has been called cannabis intoxication ever since Moreau de Tours in 1845.
The “real” effects – on biological systems – and the effects
experienced by users can vary based on a set of factors, such as the user’s
experience with cannabis and other drugs (including tobacco), the user’s
expectations and the context of use. In fact, [translation] “the
psychoactive effects of cannabis, more than any other substance, vary from one
subject to another and, for the same subject, from one experience to
Additionally, with no reliable method to measure THC content in plasma, it is
difficult to link the duration and strength of effects to the various cannabis
preparations, in particular because of variations in the composition of the
substance and in the bioavailability of THC. It is even more difficult to
attribute relatively rare effects (for example, the appearance of psychotic
symptoms) insofar as it is hard to decide if the co-occurrence is
coincidental, if these effects stem from other substances often associated
with cannabis use or from very high doses of cannabis, or from interactions
between these various factors.
The acute effects
of cannabis are relatively well documented. Research sometimes distinguishes
between central and peripheral effects,
sometimes between somatic effects and psychological or psychomotor effects,
and sometimes is simply content to list the effects of one type or another.
intoxication is generally considered to consist of two main phases:
The first phase, the
“high”, includes the following effects:
A change in general mood,
accompanied by gaiety or even hilarity, talkativeness, and a carefree feeling
A change in physical
experience, including a feeling of well-being and satisfaction, a feeling of
calm and relaxation, sociability
Alteration of intellectual
functions, including increased self-confidence, magical thinking (feeling of
being able to perform tasks more easily), distorted perception of time, space
Sensory changes, marked by
increased sensory perceptions (colours, sounds sometimes seem more intense),
stronger tactile impressions.
The second phase,
“coming down”, is characterized by a feeling of sluggishness or drowsiness
that appears gradually a little while after use.
depending on their type of action, a distinction is made between truly somatic
effects and more psychological ones.
approximately 10 minutes after use, heart rate, cardiac output and cerebral
blood flow increase. Tachycardia (accelerated heart rate) can achieve
increases of 20% to 50% compared to normal rhythm and could help trigger
anxiety and panic attacks in some subjects. It can be responsible for
palpitations, reduced exercise tolerance in subjects with heart conditions,
and can even facilitate the development of heart problems in subjects who are
at risk or are predisposed. A recent study suggests that the risk of
myocardial infarction increases by 4.8 times in the first hour after using
marijuana and is 1.7 times higher in the second hour, thus suggesting that
cannabis may represent a risk in the 60 minutes following its use.
Hypotension while the subject is lying down is also mentioned.
These effects vary based on the dose and concentration of THC.
the effects are similar to those of tobacco. Bronchodilator activity in the 60
minutes following use is mentioned. However this does not prevent the
inflammatory consequences of smoking cannabis nor the secondary bronchial
hyperreactivity that is translated in particular by a cough that results from
the action of the THC and the irritating potential of the products of
Ocular effects: redness of
the eyes due to vasodilation and conjunctival irritation is mentioned;
Other somatic effects:
dry mouth due to decreased saliva secretion, increased appetite due to
hypoglycemia (drop in blood sugar level), and more rarely nausea and vomiting,
diarrhea and urine retention.
Diminished short term
memory (so-called “working” memory): remembering words, pictures, stories
psychomotor performance, including diminished ability to pay attention and
concentrate, diminished reflexes, slowed reaction time, problems with
coordination of movements, and impaired and diminished ability to perform
complex tasks. Thus, a study by Fant et al. describes diminished visual
tracking in the central and peripheral fields of vision after 15 minutes,
capable of lasting for more than 5 hours.
Moreover, we note that according to professor Roques, studies on the effects
of cannabis on learning abilities, in particular short term memory and working
memory, are open to criticism from the standpoint of methodology and their
contradictory results, “the heaviest users were the least affected”.
and psychomotor effects are related to the amount of cannabis inhaled and
the concentration of THC. Thus, according to INSERM:
that corresponds to 25 puffs impairs psychomotor skills and cognitive
performance, and more markedly than consumption of 10 puffs or 4 puffs.
Maximum plasma levels then rise from 57 ng/ml (for 4 puffs from a cigarette
containing 1.75% D9THC)
to 268 ng/ml (for 25 puffs from a cigarette containing 3.55% D9THC).
Heishman et al. (1997)
established an approximate equivalence between 16 puffs at 3.55 % D9THC
and approximately 70g of alcohol. At these levels, memory, cognitive and
psychomotor performance and mood are impaired.
The cognitive and
psychomotor effects may continue for more than five hours, and some cognitive
impairment may extend for 24 hours.
doses, or with inexperienced users, cannabis may cause a certain number of
negative reactions that can even include a genuine paranoid, hallucinatory,
manic or hypomanic psychotic experience. However these experiences are brief.
Some disorders documented with high doses include:
Anxiety, even panic
Vertigo, nausea or
· Acute psychosis
These phenomena are
relatively rare (less than 1 in a thousand psychiatric admissions). Primarily,
it is difficult to establish that cannabis was the cause. In fact, in most
cases, the most likely hypothesis is that these subjects were already
predisposed, or had even already had psychotic or schizophrenic experiences.
Use of other substances, alcohol, other illicit drugs, or medications, could
also play an important role.
between cannabis use and psychosis is a very controversial issue. At the
moment, we lack a corpus of comparable, methodologically sound studies
repeatedly yielding similar conclusions. The results of existing studies are
often complex or ambiguous and the personal opinions of the researchers often
interfere with the interpretations. Further deepening our scientific knowledge
is still necessary. However, there is extensive, albeit incomplete, consensus
on the ability of heavy cannabis consumption or intoxication to induce an
acute transitory psychotic state in healthy subjects. The frequency of this
condition is unknown and the mechanisms are hypothetical. 
In accordance with
the collective expertise of INSERM, we can establish the following:
psychotic disorders caused by cannabis use are brief psychotic episodes that
last less than two months, even four months[sic], sometimes a week. The
premorbid personality does not present a pathological aspect. Regular users
are at greater risk than occasional users. Onset is abrupt, in two or three
days, with or without a recent increase in the use of toxic agents, sometimes
with a psychological or somatic precipitating factor. Some symptoms appear
more specific: behavioural problems, aggression, visual hallucinations,
polymorphic nature of the delirium along various themes, psychomotor
disinhibition. (…) Compared to a schizophrenic disorder, subjects are
younger, 20 to 30 years of age rather than 25 to 30, with a greater proportion
of poorly socialized males. 
However, here too,
the data are relatively contradictory and, according to professor Roques,
there is support for the belief that usage is more widespread among people
with previous mental disorders.
Most of the works
consulted in pharmacology, toxicology and psychiatry speak of chronic effects.
For our part, we prefer to speak of consequences
resulting from chronic use. There are two reasons for this. First of all,
because these consequences result not so much from the substance itself as
from the way it is used. Therefore we are not dealing with the effects of the
substance, but rather with the consequences that may arise from repeated, or
even heavy, use. The second reason is that, as we saw in Chapter 6,
chronic cannabis users account for a small fraction (often less than 10%) of
lifetime users of cannabis. As a result, the consequences in question in this
section concern this small portion of the population of users and not the
We feel this
distinction is fundamental because it is common, at all levels of public
discussion – whether involving politicians, the public at large, or experts
– to blame the substance – here cannabis, there alcohol or medications,
even other illicit drugs–when in fact we must learn
to distinguish between patterns and methods of use. By that we mean
at-risk behaviour, which varies with the substance of course, and which does
not depend solely on the intrinsic properties of the substance, but stems, in
an overall approach, from the relationship between the substance and its place
in society (integrated or not) from the individual’s characteristics, and
from the society in which the substance is used.
Of course by that it should be clear that we
consider as separate, for cannabis as for alcohol, use, at-risk use and heavy
use (or abuse),
and that we reject the equivalency often made between use and abuse where any
form of use is perceived as abuse. At the same time, we are aware of the
vagueness that continues to surround these various types of behaviour – or
practices – and that there is no clearly defined boundary, even less a
universal boundary, between use, harmful use and dependence. For the purposes
of this chapter, the consequences in question in the following three sections
refer, without being more specific, to chronic use (which then includes
at-risk and heavy use).
physiological consequences of the chronic use of cannabis dealt with in
scientific literature concern the respiratory system and the carcinogenicity
of cannabis, the immune system, the endocrine system and reproductive
functions and, to a lesser degree, the cardiovascular system.
Consequences for the respiratory
Except for the
nicotine in tobacco and the cannabinoids in cannabis, the smoke of these two
products shares common irritating, even carcinogenic, properties. Although not
recent, a comparative analysis of these products has shown that the
concentration of certain strongly carcinogenic ingredients such as benzopyrene
and benzanthracene is higher in cannabis smoke than tobacco smoke.
A more recent study cited by INSERM confirms this higher concentration of
benzopyrene: 2.9 micrograms/100 joints compared to 1.7 for 100
Of course, it will be argued that tobacco users generally smoke many more
cigarettes a day than even chronic users of marijuana, that it is the total
volume of toxic substances inhaled over time that counts, and that it can be
difficult to distinguish the effects of cannabis from those of tobacco since
joints often contain both products and users of cannabis are also often
However we note
other worrisome characteristics with respect to the potential effects on the
respiratory tract of smoking cannabis. First of all, the concentration of
benzopyrene in marijuana tar is 70% higher than that in the same weight of
tobacco tar. Furthermore, an equal product weight of cannabis provides up to 4
times more tar than a strong tobacco. According to a study cited by INSERM,
tar from a joint varies between 40 and 56 mg/cigarette whereas the allowable
dose for a European tobacco cigarette is 12 mg.
In addition, a marijuana cigarette is generally smoked much more completely
than a tobacco cigarette, inhalation – an important part of the ritual –
is deeper and the smoke is held in the lungs longer and the combustion
temperature of cannabis is higher than that of tobacco. Consequently, the
percentage of tar deposited in the lungs is higher after smoking cannabis (> 80%) than after inhaling tobacco (64%) and the deposits are even greater
for cannabis with a lower concentration of THC, probably because smokers draw
on the joint more.
INSERM’s report, chronic use of cannabis “results
in unquestionable bronchial disorders (…) chronic bronchitis with a chronic
cough, expectorations and a sibilant rale”
[translation], a conclusion shared by the Institute of Medicine in the United
States in its recent report on marijuana
as well as by the WHO.
Moreover, macrophages (cells that attack foreign bodies) in the pulmonary
alveoli seem to lose their ability to neutralize bacteria when exposed to
cannabis smoke, hence the greater susceptibility of the bronchi and lungs to
bacterial infections. According to some authors, in theory, a cannabis
cigarette could cause as much damage as 4 to 10 tobacco cigarettes.
This data on the reduced ability of alveolar macrophages to destroy bacteria
also suggests that cannabis could have an immunosuppressive action that
decreases the ability of the organism, here the lungs, to fight carcinogenic
The work of Tashkin
in particular, but also of other researchers, is not as confirmatory on the
effects of cannabis on the respiratory tract. Thus a recent study by Tashkin
on heavy cannabis smokers showed that there was no decrease in the forced
expiratory volume in one second to vital capacity ratio, even for those who
smoked 3 joints a day, compared to tobacco smokers who registered a
Tashkin’s team also questioned the development of emphysema in cannabis
users and bronchiole obstruction.
Similarly, a study by the Kaiser Permanent Medical Care Program revealed that daily cannabis
users who did not use tobacco were hardly more likely than non-smokers (36%
vs. 33%) to consult for colds, the flu and bronchitis.
We also note that to date, studies are contradictory about the additivity of
the effects of tobacco and cannabis.
respect to the carcinogenic potential of cannabis, there is a distinction
between the carcinogenic effects of cannabis smoke – a potential source of
lung cancer in particular – and the mutagenic effects of THC on cells.
According to the majority of authors, THC itself does not seem to be
However, cannabis smoke, like tobacco smoke, does seem to be able to
increase the incidence of cancerous tumors.
work of Fliegel
indicates that the histological changes that are considered the precursors of
carcinomata are present in chronic smokers of cannabis. This data is also
supported by clinical cases of cancers of the upper aerodigestive tract in
young adult cannabis smokers. These cancers are types rarely observed in young
Thirteen cases of brain
and neck cancer in young adults under the age of forty, eleven of whom were
daily cannabis smokers;
Ten cases of cancers of
the upper respiratory tract in young adults under the age of forty, seven of
whom were probable regular users of cannabis;
Two cases of carcinoma of
the tongue in men between 37 and 52 years of age for whom the only common risk
factor was the regular and daily use of cannabis.
We note first of
all the small number of cases, especially when compared to the large number of
cannabis users. These clinical cases also present a certain number of
important limitations: none compares the prevalence of cancer with a control
group or evaluates the use of cannabis in a standardized way. Interpretation
is also limited by the fact that the patients also smoked tobacco and drank
The data available
seems to indicate that the consequences of chronic and intense cannabis use
(several joints per day for several years) are similar to those of cigarettes
in terms of carcinogenic risks for the respiratory tract as well as the mouth,
the tongue and the esophagus.
THC is generally considered to alter the functions of certain cells, namely
lymphocytes, macrophages and polymorphonuclear cells, especially in in
vitro models. However conducting controlled studies is largely recognized
as a research priority in this field.
Consequences for the immune system
Apart from the
possible consequences for the respiratory tract defense system essentially
caused by smoke, there is no conclusive data regarding the effects of cannabis
on the immune system. Some studies on rodents show that high levels of
cannabinoids, including THC, alter cellular immunity. In some cases, the
experimental activity of cannabinoids is immunosuppressive and in others it is
stimulating. These variations depend on experimental factors such as the
concentration of the substance, the time and duration of administration, and
the type of cell function studied. Very little work has been done on humans.
According to the WHO report, if it is clear that cannabinoids have
immunomodulating effects, it is also clear that the immune system is resistant
to this substance. Several of the effects are relatively minimal and
completely reversible, and are only experienced at higher doses than those
required for the drug’s psychoactive effect in humans. Lastly, still
according to the WHO report, even with respect to the immunomodulating effects
of cannabis smoke, the studies are not conclusive and it is hard to compare
the doses used in experiments with animals to the doses used by humans. The
report concludes that rigorous studies on this question are necessary.
Consequences for the endocrine
system and reproduction
abnormalities are well documented in animals. In the male rat, decreased
testosterone secretion with testicular atrophy, impaired production, mobility
and viability of sperm, and changes in sexual behaviour have been noted with
high doses. The ovulatory cycle of the female is altered. In humans, the
results are contradictory, in particular because findings are not constant
from one study to another, but also because similar changes occur following
the absorption of prescription drugs. Furthermore, the changes observed are
often borderline normal and their clinical consequences remain controversial.
With respect to
reproduction, the fact that the active ingredients in cannabis cross the
placental barrier is well established. Nevertheless, the question of the
potential effects of cannabis on the feotus is far from resolved, especially
since the studies are methodologically poor. Thus, when studying pregnant
women who are cannabis users, the women often come from low socio-economic
backgrounds – and we know that socio-economic level is a determining factor
in the size and weight of babies – and it is difficult to isolate the effect
of other factors, including the use of tobacco and alcohol – which we know
are risk factors for premature birth, lower weight and smaller size. In fact,
studies on occasional cannabis smokers do not show any significant difference
with respect to non-smokers. All in all, most studies did not observe any
Nevertheless, reports from the WHO and the collective expertise of INSERM
conclude that, despite methodological difficulties, there is reasonable
evidence that cannabis use during pregnancy harms fetal development, in
particular restricted growth and behavioural abnormalities, but that these
abnormalities are rather minor.
As for the neonatal
consequences of cannabis use by mothers during pregnancy, longitudinal studies
on cohorts of children conducted in Ottawa since 1978 by psychologist Peter
are not conclusive. All the measurements taken reveal more similarities than
differences between the children of smokers and non-smokers. And when
differences are observed, they are minor and it is impossible to dissociate
the effects of the various substances, tobacco and alcohol in particular.
Lastly, these studies involve a small sample of children and generalizations
cannot be drawn from them. Another longitudinal study, reported by INSERM,
involving 636 subjects, concluded [translation] “there
is a significant relationship between behavioural problems at age 10 and
prenatal exposure to cannabis.” However the report from INSERM also
notes that [translation] “if the results from these two studies seem to converge well (…) we
must remember nevertheless that the postnatal environment can play an
important role in the continuation of behavioural abnormalities.”
Consequences for the cardiovascular
Chronic use of
cannabis may lead to cardiovascular complications for predisposed individuals.
In fact, the use of significant quantities can slow the heart rate. Also,
cannabis can have similar effects to those of tobacco on heart function by
increasing the muscle workload. Furthermore, some studies point out the role
that the carbon monoxide found in cannabis smoke plays in the risk of
The main cognitive
and psychological consequences of chronic cannabis use concern brain functions
involved in memory and verbal and math skills; motivation; and psychiatric
We have seen that
cannabis has acute effects on short-term memory, attention and concentration.
Does chronic use eventually result in effects on cognitive function that may
be irreversible? These questions first raise the question of the neurotoxicity
of cannabis, defined as “a reversible
or irreversible impairment of the structure and/or functions of the central
(and/or peripheral) nervous
system by physical, chemical or biological agents”
to professor Roques:
dependence does not result in neurotoxicity (…). Thus old results suggesting
anatomical changes in the brain of chronic cannabis users, as measured by
tomography, have not been confirmed by precise modern techniques of
neuro-imaging. Similarly, morphological changes in the hippocampus of the rat
following administration of very high doses of THC (Landfield et al., 1988)
have not been repeated (Slikker et al., 1992). (…) Several studies have been
devoted to the effects of cannabis on evoked responses and on
electroencephalograms of humans. Intermittent use produces reversible changes
wave patterns in the frontal cortex, probably with respect to the state
of drowsiness induced by THC. In the very long term (more than fifteen years)
and with heavy daily use, d hyperfrontality and an increase in q
frontal activity have been observed (Struve et al., 1990, 1994). The possible
connection with behavioural changes and changes in neuropsychological tests is
not in question, nor moreover is that which is possible with the
anticonvulsive effects of THC. 
The results of
studies reported by the collective expertise of INSERM are contradictory as
some observe changes while others do not. Even when changes are observed, they
are often of minor amplitude and are reversible after a period of abstinence.
The INSERM report observes that studies using neuro-imaging techniques have
not confirmed the neurotoxicity of cannabis in either man or baboon.
Therefore it is through observing functioning and behaviour that we are still
best able to examine the question of the neurological effects of cannabis.
studies are just as contradictory here and the results are inconclusive.
Studies performed in the 1970s in countries where cannabis use is traditional
(Jamaica, Costa Rica, India) did not point out any significant differences in
cognitive functions of users and non-users, whereas more recent studies, in
particular in Costa Rica in the 1980s, did show differences: [translation] “In particular, long-term users recalled fewer words on a list they
had been shown earlier and response time was longer.”
In the United States, studies conducted in the 1970s found contradictory
results for memory functions, whereas more recent studies reported subtle
deficits in cognitive functions of heavy users after a brief period of
abstinence. Some studies also showed continued memory impairment in
adolescents after six weeks of abstinence.
studies tend to show that overall, ex-users recover all cognitive functions,
but depending on the length of use, subtle impairments can persist, in
particular with regard to the ability to process complex information.
Still according to
the collective expertise of INSERM, the age when use begins can be a
determining factor. Thus, a recent study shows the persistence of some visual
scanning impairments (related to attention) in young people who began to use
cannabis before age 16, whereas those who began use after age 16 show no
difference from non-users.
In all, we cannot
really establish that cannabis use has negative consequences for brain
functions, even in chronic users, unless use begins before age 16.
suggest the presence of an amotivational syndrome in chronic cannabis users, a
syndrome that could affect the performance of young people at school and
employees in a professional environment in particular. In its 1997 report, the
WHO pointed out that our knowledge has not advanced since its previous report
in 1981: the amotivational syndrome has still not been clearly defined, its
effects have still not been clearly distinguished from the effects of
intoxication itself, and the data available comes from clinical case reports
with no control group.
In order to evaluate
the impact of cannabis on motivation, Canadian researchers developed a study
where subjects received cannabis in exchange for work performed. Even though
it is not recent, the study is no less interesting. They observed that
subjects worked less efficiently immediately after using cannabis. However,
their level of productivity then increased rapidly and exceeded levels
achieved during periods of abstinence. Although working fewer hours, the
subjects using cannabis were not less productive because they worked harder.
Furthermore, over the course of the period of heaviest use, the subjects
organized a strike and successfully negotiated a “salary” increase, after
which they worked even harder.
Studies do not
enable us to establish if motivational problems, when observed, preceded or
followed cannabis use, or if other emotional or psychosocial factors played a
greater role, or were even determining factors in the chronic use or abuse of
cannabis in young people in particular. These conclusions are shared by the
collective expertise of INSERM and by the authors of the report submitted to
the International Scientific Conference on Cannabis in March 2002.
disorders have been associated with chronic cannabis use: mood disorders and
depressive episodes, anxiety disorders, personality disorders, as well as more
severe conditions, such as psychoses and schizophrenia. For each of these
situations, the conclusion drawn by the authors of the report on mental health
and cannabis prepared for the International Scientific Conference on Cannabis
three possible ways to account for the relationship between cannabis and mood
disorders. First, both may share common risk factors, so that their
relationship is not causal. Second, mood disorders may predispose people to
use cannabis. Third, cannabis use may trigger or increase depressive symptoms.
As yet, there is no clear answer to this question of “which comes first”. 
with regard to mood disorders, depressive states and anxiety disorders, it
seems probable that they precede chronic use. However, study results are
extremely disparate: for mood disorders in so-called dependent people, the
prevalence varies (depending on study methods), from 10% to almost 50%; with
respect to major depressive episodes in clinical populations, studies report
percentages varying from 4% to almost 20%. INSERM’s report presents a review
that we feel is much more enlightening with regard to the situation for
[Translation] Acquiring new
knowledge has allowed for a better assessment of the burden of “early onset
depression” in terms of individual suffering and public health. Its
prevalence, around 5% in adolescence, makes it one of the most common
pathologies for this period. The risk of suicide is high, and the functional
deficits inherent in depressive syndromes are a source of school and family
problems, and cause withdrawal from peers, for which the psychosocial
consequences can be severe, especially if the disorder is prolonged.
Additionally, depression is rarely an isolated disorder in a young subject:
anxiety or behavioural disorders often precede or accompany depressive
episodes and can survive them; moreover, the existence of a depressive
disorder is a risk factor for addiction (alcohol or any other psychoactive
substance) and eating disorders. 
respect to psychotic disorders and schizophrenia, the two subjects are
controversial, the methodologies weak, the data contradictory and the
interpretations are often based on simplistic models of causality. If, in
certain circumstances, cannabis can trigger psychotic episodes, they are most
often short and resolve rapidly. As for schizophrenia, if it is true that
cannabis use is more prevalent in these subjects than in the general
population, some feel that it is self-medicating behaviour while others feel
that the chronic use of cannabis is a trigger for the schizophrenic process.
We feel that the conclusion of professor Roques’ report agrees best with
[Translation] No mental
pathology directly related to the overuse of cannabis has been reported, which
distinguishes this substance from psychostimulants such as MDNA, cocaine or
alcohol, heavy and repeated use of which can give rise to characteristic
psychotic syndromes. Similarly, cannabis does not seem to precipitate the
onset of pre-existing mental dysfunctions (schizophrenia, bipolar depression,
As it is, most
scientific reports come to the same conclusion: more research is needed, with
more rigorous protocols, allowing in particular for comparison with other
populations and other substances.
behavioural and social consequences examined in scientific literature deal
with social and family adjustment, aggression, and the ability to perform
Social and family adjustment
According to some
studies, chronic cannabis use could have consequences for social and family
adjustment. Thus chronic users would have more difficulty keeping a job, would
be unemployed more often and would have more interpersonal adjustment
However, most of
these studies suffer from methodological problems and interpretation
difficulties. Most studies involve samples of people who, by and large, come
from underprivileged socio-economic backgrounds. Above all, beyond the
statistical association, it is difficult to determine to what extent other
factors play a preponderant role, of which cannabis is itself a symptom and
not a cause.
psychoactive substances, alcohol and cocaine in particular, cannabis does not
lead to aggression. When examining withdrawal symptoms once dependence is
established, some authors note greater irritability; but this is even less
significant proportionally than that caused by tobacco.
Performing complex tasks
No study on chronic
cannabis use has been able to establish that cannabis causes long-term effects
on the ability to perform complex tasks. This data is in keeping with
cannabis’ lack of neurotoxicity.
Tolerance and dependence
When we think drugs
we think drug addiction since, as F. Caballero states, a drug is [translation]
“any substance likely to lead to
In France and Europe, monitoring groups created in recent years are called
monitoring centres for drugs and drug addiction. In Quebec, the advisory body
created by the government is called the “Comité
permanent de lutte à la toxicomanie” [standing committee on the fight
against drug addiction]. The expression “drug addiction” is found
everywhere: in legislation, in information documents, and in everyday
language. However, since 1963, the WHO has recommended that we abandon this
expression because it is imprecise and refer instead to states of physical and
psychic dependence, defined as follows:
dependence is a “condition in which a drug produces a feeling of
satisfaction and a psychic drive that requires periodic or continuous
administration of the drug to produce pleasure or to avoid discomfort.
Physical dependence is an “adaptive state that manifests itself by intense
physical disturbance when the administration of the drug is suspended or its
action is opposed by a specific antagonist. These disturbances, that is the
abstinence or withdrawal symptoms, consist of physical and psychic symptoms
and signs that are characteristic for each drug. [translation]
the extension of the notion of drugs to other substances (pharmaceutical
products, tobacco, alcohol), and with the extension of international control
of substances to psychotropic drugs, in 1969 the WHO created a new definition
for the term drug dependence that, though its application was initially
limited to medication only, has come to be more widely accepted over time:
dependence. A state, psychic and sometimes also physical, resulting from the
interaction between a living organism and a drug, characterized by behavioural
and other responses that always include a compulsion to take the drug on a
continuous or periodic basis in order to experience its psychic effects, and
sometimes to avoid the discomfort of its absence. Tolerance may or may not be
present. A person may be dependent on more than one drug. 
But it is even more
interesting for our purposes to quote even older definitions from the WHO
dealing with habituation and addiction:
habituation (habit) is a condition resulting from the repeated
consumption of a drug. Its characteristics include:
A desire (but not a compulsion) to continue taking the drug for the
sense of improved well-being which it engenders;
Little or no tendency to increase the dose;
Some degree of psychic dependence on the effect of the drug, but
absence of physical dependence and hence of an abstinence syndrome;
Detrimental effects, if any, primarily on the individual.
addiction is a state of periodic or chronic intoxication produced by the
repeated consumption of a drug (natural or synthetic). Its characteristics
An overpowering desire or need (compulsion) to continue taking the drug
and to obtain it by any means;
A tendency to increase the dose;
A psychic (psychological) and generally a physical dependence on the
effects of the drug;
Detrimental effect on the individual and on society. 
This definition is
important because, more than the previous two, it allows us to better
distinguish between drugs that create primarily a habit and those that create
an addiction, that is, the overwhelming need to use them. Now, as we will see
in this chapter, cannabis corresponds much more to the criteria of a substance
likely to create some degree of habituation and not an addiction.
In addition to drug
addiction, thinking about drugs means also thinking about illicit substances.
Now, as a wide range of works and an increasing number of practices have
established, for practical purposes, the actual distinction is made on the
combined levels of the substance’s toxicity (its dangers) and the uses (use,
abuse, heavy use) that characterize it, not on the level of its legal and
Let us first
establish that animal studies on dependence and withdrawal are not very
pertinent since most of them use doses that have nothing in common with the
doses used by humans, even chronic users. Moreover, we note that studies on naïve
animals (no experience with other drugs) have not been able to establish
self‑administering behaviour and that is the only technique that allows
for the direct assessment of the reinforcing properties of a molecule. One of
the probable explanations stems from the long plasma half-life of D9THC,
which we know is eliminated slowly by an organism (up to 25 days as we saw in
the Chapter 5).
We also note that even after administration of very high doses of D9THC,
somatic signs of spontaneous withdrawal were not observed in rodents, pigeons,
dogs or monkeys.
Lastly, we note that all in all, we know little about the biophysiological and
psychological mechanisms of dependence.
The idea of cannabis
dependence has been the subject of criticism due to its overly medical aspect
(having little regard for the differences in social context of the ways and
situations in which it is used) and circular reasoning (for example, the fact
that drugs are illegal means that their use is necessarily illegal, yet this
is one of the criteria for dependence).
Nevertheless, when measured in accordance with the criteria of the DSM, a
cannabis dependence syndrome presents no differences from an alcohol or heroin
dependence syndrome. Furthermore, establishing the relative dangers of
cannabis is not contrary to the objectives of public health.
criteria of the DSM-IV (Diagnostic and
Statistical Manual of Mental Disorders) of the American
Psychiatric Association undoubtedly remain the most widely used in studies
on dependence, especially since the majority of drug research is conducted in
the United States and Commonwealth countries (England, Australia, Canada…)
that use this instrument.
distinguishes between criteria for substance abuse and criteria for
dependence. We have reprinted them here in accordance with the INSERM report.
Criteria for Substance Abuse according to the DSM-IV
maladaptive pattern of substance use leading to clinically significant
impairment or distress, as manifested by one (or more) of the
following, occurring within a 12-month period:
substance use resulting in a failure to fulfill major role obligations
at work, school, or home;
substance use in situations in which it is physically hazardous;
substance-related legal problems;
substance use despite having persistent or recurrent social or
interpersonal problems caused or exacerbated by the effects of the
symptoms have never met the criteria for Substance Dependence for this
class of substance.
Criteria for Substance Dependence according to the DSM-IV
A maladaptive pattern of substance use, leading to clinically
significant impairment or distress, as manifested by three (or more) of
the following, occurring at any time in the same 12-month period:
as defined by either of the following:
need for markedly increased amounts of the substance to achieve
intoxication or desired effect;
diminished effect with continued use of the same amount of the
as manifested by either of the following:
characteristic withdrawal syndrome for the substance;
same (or a closely related) substance is taken to relieve or avoid
substance is often taken in larger amounts or over a longer period than
is a persistent desire or unsuccessful efforts to cut down or control substance
great deal of time is spent in activities necessary to obtain the
substance, use the substance, or recover from its effects;
social, occupational, or recreational activities are given up or reduced
because of substance use;
substance use is continued despite knowledge of having a persistent or
recurrent physical or psychological problem that is likely to have been
caused or exacerbated by the substance.
The existence of a
cannabis dependence syndrome in humans can be inferred using various methods:
epidemiological investigations and clinical studies (which usually use DSM
criteria), and requests for treatment.
studies show that cannabis use can lead to psychological dependence. In some
cases, they estimate that half of chronic users would develop this kind of
People who use cannabis on a daily basis for several months would be at
greater risk of becoming dependent.
Interpretation and intercomparison of the various studies is difficult because
the denominator is not always common, or even specified (in some cases, it is
the general population while in others it is cannabis users and in the latter
case, there is not always a distinction among life-long, recent and regular
users). The authors also do not always specify if the dependence is recent or
In the United States,
several investigations were conducted into the frequency of use of various
psychoactive substances and dependence. Through the Epidemiological
Catchment Area study, close to 20 000 people were interviewed in five
years during the 1980s. The prevalence (in the general population) of cannabis
dependence was 4.4%.
The National Comorbidity Survey, an
investigation to estimate the comorbidity between substance abuse and other
mental disorders, undertaken between 1990 and 1992 and involving more than
8,000 subjects from the general population between the ages of 15 and 55,
also estimated the prevalence of dependence. For the purposes of the
investigation, DSM criteria were used and dependence was observed when
respondents presented at least three of the nine criteria. According to this
study, 4.2% of the 15‑54 year olds presented cannabis dependence
(14% were dependent on alcohol and 24% on tobacco). Of those who had used
cannabis at least once during their life (46%), 9% were considered dependent,
compared to 32% for tobacco and 15% for alcohol. Cannabis dependence was more
common in men than women (12% versus 5.5% of users), and in those 15-24 than
in the others (15% versus 8%). Combining the results of
three large investigations into the use of psychoactive substances conducted
on households (nearly 88,000 respondents aged 12 and up) Kandel et al. observed that 8% of those
who had used cannabis in the previous year (0.7% of the sample) were
In New Zealand, a
longitudinal study involving a cohort of 1,265 children born in 1977 in an
urban setting and followed since birth revealed that at age 21, not less than
70% had used cannabis. Of those, 13% had had a problem with dependence
measured in accordance with the DSM-IV during their lifetime.
Another New Zealand study involving a cohort of 1,000 people found similar
results: at age 21, 62% had used cannabis and at age 26, 70% had. The
prevalence of dependence using DSM III-R criteria went from 3.6% at age 18 to
9.6% at age 21 (or nearly 15% of users).
In Australia, an
investigation involving more than 10,000 people from the general population
who were over 18 years of age showed that approximately 1.5% of users during
the previous year and 20% of current users showed signs of dependence based on
In the Netherlands, a
study involving a sample of the national population aged 18 to 65 (7,000
subjects) showed that 10% of users had had signs of dependence during their
It is difficult to
generalize based on the results of clinical studies, but it is interesting to
see to what extent their results are similar to those of epidemiologic
studies. Kosten examined the validity of DSM-III R criteria to identify
syndromes of dependence on various psychoactive substances including cannabis.
He observed that the criteria for syndromes of alcohol, cocaine and opioid
dependence were strongly consistent. The results were more ambiguous for
cannabis. A criterion-referenced analysis revealed that there were three
dimensions to the cannabis dependence syndrome: (1) compulsion – indicated
by a change in social activities attributable to the drug; (2) difficulty
stopping – revealed by the inability to reduce use, a return to previous
levels after stopping temporarily and a degree of tolerance of the effects;
and (3) withdrawal signs – revealed by their disappearance with re-use and
continuing use despite recognized difficulties.
Studies on long-term
Canada, Hathaway conducted a study between October 2000 and April 2001 to
identify problem use and dependence in long-term users based on the DSM-IV
The sample was made of 104 individuals (64 men and 40 women) aged 18 to 55
(mean age 34). 80% had used cannabis on a weekly basis, 51% on a daily basis
during the preceding 12 months, and close to half (49%) had used one ounce (28 grams)
or more per month. Reasons to use included: to relax (89%), to feel good
(81%), to enjoy music or films (72%), because they are bored (64%) or as a
source of inspiration (60%).
were asked if they had ever engaged in deviant activity related to cannabis
use. The most frequent answer was to have been in an uncomfortable situation
in order to get cannabis. Other activities included borrowing money, selling
cannabis to support their own drug use, and taking on extra work to buy
cannabis. Only 6% ever had recurring legal problems due to their use of
cannabis. With respect to dependence, 30% reported a lifetime prevalence of
three or more of the criteria, 15% during the 12 months prior to the
light of this finding, the most frequently encountered problems with cannabis
have more to do with self‑perceptions of excessive use levels than with
the drug’s perceived impact on health, social obligations and relationships,
or other activities. Lending support to the highly subjective nature of his
evaluative process, no significant correlations were found between amounts nor
frequency of use and the number of reported DSM-IC items. For those whom
cannabis dependency problems progress to the point of seeking out or
considering formal help, however, the substantive significance of perceived
excessive use levels cannot be overlooked. 
comparative study by Cohen and Kaal presented in the previous chapter also
included data on dependency symptoms. Between 21% and 24% of the subjects
presented 3 or more DSM-IV criteria in their lifetime as the following table
Number of positive DSM IV
Amsterdam, San Francisco,
Number of criteria
Average incl. 0
Average excl. 0
authors observe a significant correlation between amount of cannabis use (in
grams) during top period of use and the number of DSM-IV items ever
experienced. However, no correlation was found between the amount of cannabis
use during top period of use and number of criteria experiences in the last
Requests for treatment
Lastly, we can
examine dependence indirectly through requests for treatment. Obviously, this
is a very indirect and definitely very imperfect means for several reasons.
The very great majority of cannabis users use it irregularly and stop when
they reach their twenties. Of those who continue and become regular users, we
have just seen that between 10% and 20% will present the criteria for
dependence. Most users do not think they need help, which their ability to
stop without outside assistance would confirm. Lastly, those who ask for help
could be influenced simultaneously by the availability of services as well as
the interaction of other problem substances, alcohol, medication or other
drugs, or other mental disorders. In fact, it seems that in a significant
proportion of cases, requests for treatment related to cannabis come from
people with multiple disorders.
Nevertheless, we have
heard testimony to the effect that requests for treatment for problems with
cannabis dependence are on the rise and that this increase could be related to
the THC content.
In Europe, requests
for treatment where the main problem is cannabis-related vary widely from
country to country, ranging from 6% in Spain (one of the countries where use
is most widespread and most tolerated) to 25% in Belgium. Sweden, which
however has a relatively low rate of use, is at 14%, comparable to France
(16%) which, however, has a much higher rate of use. In the United States,
demand is just as variable depending on the state, from 5% to 30%.
dependence has been evaluated in different ways. In the United States, a study
examined approximately 1,100 subjects who had used cannabis more than six
times and evaluated the severity of their dependence based on DSM-IV criteria.
The level of dependence (low, intermediate or high) corresponded to the number
of criteria met. The following results
Severity of cannabis dependence
based on use
of subjects based on type of use
(number of criteria)
T = tobacco; A = alcohol; C = cannabis
We see a consistent
situation in which the link between heavy use and dependence is lower for
cannabis than for tobacco and alcohol, and in which, over all, dependence on
cannabis is the lowest of the three substances.
For his part,
professor Roques proposes three classes of products based on their dangers.
The first includes heroin, cocaine and alcohol; the second psychostimulants,
hallucinogens, tobacco and benzodiazepines; and cannabis is set apart in a
separate class. He classifies the dangerousness of drugs using a diverse set
of criteria. We have reprinted his table of the dangerousness of drugs on the
Danger Factors of “drugs”
(reprinted from Roques, B. (1999), page: 296
Hypersensi-tivity to Dopamine
Activation of Opioid System
Danger to Society
high ( ?)
In closing, we note that there is no known physical dependence on
cannabis, even though in the most severe cases, withdrawal is sometimes
accompanied by physical signs such as trembling, insomnia, irritability, etc.
a technical standpoint, tolerance is defined as follows:
property of the human organism to endure the administration of usually effective
doses of a given substance without displaying a reaction. With respect to drugs,
this tolerance can lead to increased doses in order to achieve the desired
of tolerance is associated with pharmacodynamic changes. In some animal studies,
chronic administration of THC reduced the density of receptors in some regions
of the brain
and increased it in others; these effects were reversible.
man as in animals, studies have observed the phenomenon of cannabis tolerance.
However, the data must be interpreted with care insofar as some studies and
clinical cases have also found that regular users needed less cannabis to
achieve the desired effect.
Nevertheless, a study by Wiesbeck et al. involving 5,611 subjects reported that
16% of frequent cannabis users had a history of a withdrawal syndrome.
is tolerance of a substance that leads to withdrawal symptoms. In recent years,
clinical data has been accumulated on withdrawal symptoms in heavy cannabis
users (several doses per day in an ongoing manner for several years). The
symptoms observed include agitation, loss of appetite, nausea, disturbed sleep,
irritability or hyperactivity and an increased body temperature.
These symptoms appeared after 24 hours of abstinence, peaked after two to four
days and diminished within seven days. The symptoms were markedly less severe
and of shorter duration than with other psychoactive substances. Furthermore,
clinical studies showed that most subjects continued to perform their daily
activities in a normal fashion.
Chapter 6, we have seen that use does not follow a single pattern, even less so
a pattern inevitably leading to increased use. Even in chronic users, the use of
cannabis is sometimes irregular and involves periods of abstinence and of more
intensive use. We have also seen that current epidemiological studies are not
sensitive enough to the complex interactions between the multiple factors that
influence patterns of use. These various difficulties make it more difficult to
estimate the number of problem users, even more so the number of persons who may
our view, it is clear that the term addiction, severely criticized for its
medical and moral overtones, is inadequate to properly describe the different
forms of at-risk and problem uses. It is even less useful when it comes to
cannabis, whose addictive potential is low. It is therefore of limited use to
inform public policies aiming to prevent at-risk and problem use and to assist
excessive users. Further, we are of the view that dependency is but one of the
many consequences of excessive use of cannabis and that this possibility must
not be overestimated.
these reasons, we propose to distinguish between different uses on the basis of
four criteria: context, quantity, frequency, and duration and intensity.
Proposed Criteria for Differentiating Use Types
Period of use and intensity
Experimental / Occasional
few times over lifetime
in a group
than one gram per month
few times per month
over several years but rarely intensive
and occupational (to go to school, to go to work, for sport…)
Alone, in the morning
16 years of age
0.1 and 1 gram per day
few times per week, evenings, especially weekends
over several years with high intensity periods
and personal problems
self regulation of use
one gram per day
than once per day
over several years with several months at a time of high intensity use
the poor knowledge base on use patterns in Canada, we have no choice but to
speculate on the number of persons falling in each of these types of uses. We
propose the following broad parameters:
In adults: we
have estimated that approximately 100,000 persons over 18 would use cannabis
If 30% to 40%
use between 0.1 to 1 gram per day, this means that 30,000 to 40,000 may be
If 5% to 10%
use more than 1 gram per day, this means that 5,000 to 10,000 adults have
excessive use patterns.
In youth 12 to
17, we have estimated that as many as 225,000 use cannabis daily.
If it is agreed
that any use below the age of 16 is excessive use, and that youths 12-15 who use
cannabis may represent approximately 25% of this group, then about 50,000 may
remaining 175,000, if 30% to 40% use 0,1 to 1 gram per day, approximately 50,000
to 70,000 would be at-risk;
If 5% to 10% of
the remaining 175,000 use more than 1 gram per day, then approximately 8,000 to
17,000 use excessively.
are aware that these estimates do not account other variables, such as context
and duration of use. We can only hope that future epidemiological studies, which
must be undertaken regularly, will help further explain the complexity and
variability of these uses.
In total, based on
all the data from the research and the testimony heard regarding the effects and
consequences of cannabis use, the
Committee concludes that the state of knowledge supports the belief that, for
the vast majority of recreational users, cannabis use presents no harmful
consequences for physical, psychological or social well-being in either the
short or the long term.
this conclusion is based on the following conclusions.
Conclusions of Chapter 7
effects of cannabis
use and heavy use in adults
use in those under age 16 is high-risk use
of heavy use
Ø The immediate effects of cannabis are characterized by feelings of euphoria, relaxation and sociability; they are accompanied by impairment of short-term memory, concentration and some psychomotor skills.
Ø For purposes of public policy, the Committee does not feel that the traditional distinctions between acute and chronic effects are useful.
Ø Similarly, the Committee does not feel the dichotomy of use and dependence is useful.
Ø The research data does not allow for a clear distinction between use, at-risk use and heavy use.
Ø The amount consumed is an indicator, but other factors, psychosocial factors and factors relating to the context of use and the quality of the substance, are equally determining in the passage from use to at-risk use and heavy use.
Ø Nevertheless, the Committee feels that for people over the age of 16, at-risk use lies within the range of 0.1 to 1 gram per day; anything more than that is heavy use, which can have negative consequences on the physical, psychological and social well-being of the user.
Ø According to this distinction, and in accordance with the epidemiological data available, there is reason to believe that approximately 100,000 Canadians could be at-risk users and approximately 80,000 could be heavy users.
Ø The Committee feels that, because of its potential effects on the endogenous cannabinoid system and cognitive and psychosocial functions, any use in those under age 16 is at-risk use;
Ø Our estimation would suggest that approximately 50,000 youths fall in this category.
Ø For those between the ages of 16 and 18, heavy use is not necessarily daily use but use in the morning, alone or during school activities;
Ø Heavy use of smoked cannabis can have certain negative consequences for physical health, in particular for the respiratory system (chronic bronchitis, cancer of the upper respiratory tract).
Ø Heavy use of cannabis can result in negative psychological consequences for users, in particular impaired concentration and learning and, in rare cases and with people already predisposed, psychotic and schizophrenic episodes.
Ø Heavy use of cannabis can result in consequences for a user’s social well-being, in particular their occupational and social situation and their ability to perform tasks.
Ø Heavy use of cannabis can result in dependence requiring treatment; however, dependence caused by cannabis is less severe and less frequent that dependence on other psychotropic substances, including alcohol and tobacco.
World Health Organization (1997), op. cit., page: 3; on this question also
see: Hall, W. (1987) “A simplified logic of causal inference” Australian
and New Zealand Journal of Psychiatry, 21: 507-513.
On this subject, see the works of Karl Popper in particular (1978 for
the French edition) The Logic of
Scientific Discovery Paris: Payot, and (1985) La
connaissance objective. Bruxelles: Complexe.
It is even a little ironic that the National Institute on Drug Abuse
(NIDA) in the US finances studies that have people smoke when the Institute
believes that cannabis is a gateway drug: for example, see the study by
Haney, M. et al. (1999) “Abstinence symptoms following smoked marijuana in
humans” Psychopharmacology, 141;
Nelson, P.L. (1993) “A critical review of the research literature
concerning some biological and psychological effects of cannabis” in
Advisory Committee on Illicit Drugs (eds.) Cannabis
and the law in Queensland: A discussion paper. Brisbane: Criminal
Justice Commission of Queensland.
Wheelock, B. (2002) op. cit.
In particular the previously mentioned INSERM report (2001), op. cit. and the report from the International Scientific Conference
on Cannabis (2002); as well as the report from the National Institute of
Medicine in the US and the book edited by Professor Kalant, one of our
Testimony of Michael J. Boyd, Chair of the Drug
Abuse Committee and Deputy Chief of the Toronto Police Service, for
the Canadian Association of Chiefs of Police, Special Senate Committee on
Illicit Drugs, First Session of the Thirty-Seventh Parliament, Issue No. 14,
Testimony of Dale Orban, Detective Sergeant, Regina Police Service, for the
Canadian Police Association, Special Senate Committee on Illicit Drugs,
First Session of the Thirty-Seventh Parliament, Monday, May 28, 2001, Issue
3, page: 47. It should be immediately noted that the last statement is
completely false as we will see in Chapters 19 and 12 on international
agreements and Canadian legislation that have placed cannabis on the list of
controlled drugs since 1924, with no knowledge of its physical or
psychological effects at that time, and for completely different reasons,
when there were any.
Dr. Mark Zoccolillo, Professor of Psychiatry and Assistant Professor
of Pediatrics, McGill University and the Montreal Children's Hospital,
Special Senate Committee on Illicit Drugs, Second Session of the
Thirty-Sixth Parliament, October 16, 2000, Issue No. 1, page 77.
Dr. Bill Campbell, President, Canadian Society of Addiction Medicine,
Special Senate Committee on Illicit Drugs, First Session, Thirty-Seventh
Parliament, March 11, 2002, Issue No. 14, page: 56.
Mr. John Conroy, Barrister, Special Senate Committee on Illicit
Drugs, First Session of the Thirty-Seventh Parliament, March 11, 2002, Issue
No. 14, page 11.
Dr Colin Mangham, Director, Prevention Source BC., Special Senate
Committee on Illicit Drugs, First Session of the Thirty-Seventh Parliament,
September 17, 2001, Issue No. 6, page: 71.
Dr. Benedikt Fischer, Professor, Department
Sciences, University of Toronto, Special
Senate Committee on Illicit Drugs, First Session of the Thirty-Seventh
Parliament, September 7, 2001, Issue No. 6, page 9.
Dr. Perry Kendall, Health Officer for the Province of British
Columbia, Special Senate Committee on Illicit Drugs, First Session of the
Thirty-Seventh Parliament, September 17, 2001, Issue No. 6, pages 33-33.
Dr. Harold Kalant, Professor Emeritus at the University of Toronto,
Special Senate Committee on Illicit Drugs, First Session of the
Thirty-Seventh Parliament, June 11, 2001, Issue No. 4, pages 74-76.
Dr. Mohamed ben Amar, Professor of Pharmacology and Toxicology,
University of Montreal, Special Senate Committee on Illicit Drugs, First
Session of the Thirty-Seventh Parliament, June 11, 2001, Issue No.
4, pages 9-10.
 Moreau de Tours, J., Du haschich ou de l’aliénation mentale, étude psychologique. Paris: Masson.
 INSERM, op. cit., page 118.
See WHO, 1997, op. cit., 3.
For example, this is the case with the classification proposed by Ben
Amar (at press).
This is the case with the collective expertise of INSERM (2001).
This is the case with most works: WHO, 1997; Swiss Federal Commission
for Drug Issues (1999) Rapport sur le
cannabis. Berne: Swiss Federal Office of Public Health; and the report
by Wheelock (2002).
Fant, R.V. et al. (1998)
“Acute and residual effects of marijuana in humans.” Pharmacology, Biochemistry and Behavior, 60: 777-784.
 Roques, B. (1999) La dangerosité des drogues. Paris: Odile Jacob, page: 184.
INSERM, op. cit., page:
Hanak, C. et al. (2002)
“Cannabis, mental health and dependence.” in Pelc, I. (ed.), International
Scientific Conference on Cannabis, Brussels.
INSERM, op. cit., page 124.
Roques, B., op. cit., page
 This question has been discussed more fully in Chapter 6. For now it is enough to refer the reader to the work of Reynaud et al. (1999) Les pratiques addictives. Usage, usage nocif et dépendance aux substances psycho-actives. Paris: La Documentation française.
We will more clearly establish the parameters we used to make this
distinction in the next chapter on use and users. Further on in this chapter
we will see that dependence is a consequence of heavy use.
Institute of Medicine (1982) Marihuana
and Health. Washington, DC: National Academy of Sciences.
INSERM (2001), op. cit., page 222.
For example, those are the criticisms made by Zimmer L., and J.P.
Morgan (2000 for the French version; 1997 for the American original) Marijuana. Mythes
et réalités. Paris:
Ibid., page 221.
Ibid., page 221
Ibid., page 218.
Joy, J.E. et al., (1999) Marijuana
and Medicine: Assessing the Science Base. Washington, DC: Institute of
WHO (1997) op. cit.
Ben Amar (at press), op. cit.,
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Polen, M.R. (1993) “Health care use by frequent marijuana smokers
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cit. for the Senate Committee.
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Wheelock, B. (2002), op. cit., page
WHO (1997), op. cit., page:
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WHO (1997), op. cit., page
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