In the 1990s, cannabis is in the news again as research reveals
an upturn in use and governments struggle to develop a policy
response that weighs the potential harm of the drug against the
potential harm of drug policy itself.
Cannabis--sold as marijuana, hashish and hash oil--is the most
frequently used illicit drug in Canada. Roughly one in four Canadian
adults report having used cannabis at some time in their lives. And
use has been on the rise among young people. For example, a 1997
Addiction Research Foundation (ARF) survey found that 25 percent of
Ontario junior high and high school students used cannabis in the
previous year, up from 13 percent in 1993.
One feature of the renewed interest in cannabis is the frequency
with which questions on the subject have been put to political
candidates. Their responses--often including admissions of cannabis
use--are typically lighthearted, but the humor is perhaps lost on
the hundreds of thousands of Canadians with criminal records for
cannabis possession.
In October, 1995, Canada's House of Commons passedThe Controlled
Drugs and Substances Act, a law criticized for its continuing harsh
approach to cannabis possession.
To deal with ongoing concerns about cannabis policy, the basic
questions that must be addressed remain the same:
What do we know about the health risks associated with cannabis
use?
What is the most effective and least costly way to minimize
these risks?
What is the most effective way to minimize potential harms
resulting from our drug policy response?
Some health consequences of cannabis are clearly known, while
others--such as the effects of chronic exposure--are less obvious..
There is no doubt that heavy cannabis use has negative
health consequences. (For detailed documentation of research and
reference material, please see Hall et al, 1994, and WHO, in
preparation). The most important effects are:
Respiratory damage: Marijuana smoke contains higher
concentrations of some of the constituents of tar than tobacco
smoke. As well, it is hotter when it contacts the lungs and is
typically inhaled more deeply and held in the lungs longer than
tobacco smoke.
Research has shown a link between chronic heavy marijuana use
and damage to the respiratory system similar to that caused by
tobacco..
Long-term marijuana smoking is associated with changes--such as
injury to the major bronchi--that leave the lungs open to injury
and infection. Frequent, heavy use has been linked with bronchitis
(Bloom et al., 1987; Tashkin et al., 1988.) There is no
established link between marijuana smoking and lung cancer. But
case reports of some cancers in young adults with a history of
cannabis use are of concern. (Polen et al., 1993).
These adverse effects are, of course, related to smoking the
drug, and don't occur when cannabis is eaten.
Physical co-ordination: Cannabis impairs co-ordination.
This brings with it the risk of injury and death through impaired
driving or accidents such as falls.
North American studies of blood samples from drivers involved
in motor vehicle crashes have consistently found that positive
results for THC (the mood-altering ingredient in cannabis) are
second only to positive results for alcohol. However, blood levels
of THC do not demonstrate that a driver was intoxicated at the
time of the accident..
In addition, many drivers with cannabis in their blood are also
intoxicated with alcohol.
Experimental studies of driving that show that cannabis use can
impair braking time, attention to traffic signals and other
driving behaviors . The studies found that subjects appear to
realize that they are impaired, and compensate where they can.
However, such compensation is not possible when unexpected events
occur, or if the task requires continued attention.
Pregnancy and childhood development: Cannabis use by
women who are pregnant may affect the fetus. As with tobacco
smoking, risks such as low birth weight and premature delivery
increase with use.
The longer-term effects on children whose mothers smoked
cannabis while pregnant appear to be subtle. Recent research
suggests that exposure to cannabis in the womb can affect the
mental development of the child in later years. By age four, for
example, offspring of women who used cannabis regularly showed
reduced verbal ability and memory. By school age, decreased
attentiveness and increased impulsiveness were also found in
children whose mothers used cannabis heavily (Day et al, 1994;
Fried, 1995).
Memory and thinking: The effects of cannabis on memory
appear to be variable, and may depend on the test that is used.
Overall, the effects seem to be modest. However, it's not yet
known whether chronic use would produce serious impairments of
memory, particularly is such use occurs during development.
Several years ago, studies of adult cannabis users suggested that
the drug has little effect on cognitive function. More recent
research has demonstrated that long-term use produces deficits in
the ability to organize and integrate complex information (Solowij
et al., 1995).
Psychiatric effects: Cannabis use has been linked to a
number of psychiatric effects. The most significant is called
cannabis dependence syndrome. A person with this condition will
continue to use the drug despite adverse effects on physical,
social and emotional health (Anthony and Helzer, 1991). Impairment
of the person's behavioral control, combined with effects on
thinking and motivation, can adversely affect a person's work or
studies. The risk of dependence increases with use. It has been
reported that one-third to one-half of those who use cannabis
daily for long periods may become dependent.
There is clearly a link between cannabis use and schizophrenia,
but it is not yet known whether cannabis use triggers
schizophrenia, or whether schizophrenia may lead to increased
cannabis use (Andreasson et al., 1987; Andreasson et al., 1989).
Health professionals have identified a condition of "cannabis
psychosis" following heavy use of the drug (Chaundry et al.,
1991; Thomas, 1993). The condition disappears within days of
abstinence..
However, this disorder has not been well defined, and it is not
clear that it differs from the effects of high doses of the drug.
Reference has also been made to an "amotivational
syndrome" resulting from extensive cannabis use. While heavy
use of cannabis may interfere with motivational, the existence of
a syndrome with identifiable symptoms outlasting drug use and
withdrawal has not been demonstrated. (This question may have been
clouded by studies of effects of cannabis use on educational
performance in adolescents, in which individuals most likely to
use the drug may have lower motivation to succeed academically.)
Hormone, immune and heart function: Research has shown
that cannabis can also alter hormone production, and affect both
the immune system and heart function. The implications of these
findings for human health are unclear at present.
The link between cannabis and the use of other drugs is also of
concern. In particular, people have questioned whether cannabis acts
as a "gateway drug" to heroin, cocaine or other drug use.
There is a statistical link between the use of cannabis and other
drugs. Cannabis users are more likely to use tobacco and alcohol,
for example. They are also more likely to try other illicit drugs
than those who have never used cannabis. As well, the earlier a
person uses cannabis and the more he or she consumes, the greater
the likelihood that the person will use other illicit drugs.
The reason for this link is less clear. It's likely, however,
that the use of cannabis does not in itself lead to the use of other
illicit drugs. For example, roughly one in four Canadians has used
cannabis, yet only four percent have ever used crack or cocaine.
Similarly, just two percent have ever used amphetamines and about
half of one percent have ever used heroin (Health Canada, 1995).
A more likely explanation is the cannabis use may be one of many
social and cultural factors--including family relationships, mental
health, peer influences, social attitudes and beliefs--associated
with a higher likelihood of the use other substances as well. In
other words, the same factors that contribute to cannabis use may
lead a smaller number of individuals to go on to other illicit
drugs. This may also explain the statistical link between cannabis
use and lower academic and professional achievement and other
personal and social problems.
Cannabis and other street drugs are also linked by the very fact
that they are illegal--a dealer who sells cannabis may also offer
other drugs.
Many of the negative effects of cannabis are associated with long
term heavy use. As mentioned earlier, however, most Canadians who
use cannabis do so sporadically and in small amounts. Certainly, the
typical pattern of cannabis use is much different from that of
cigarette smoking. For most marijuana users, damage to the lungs is
therefore likely to be limited.
Given the current patterns use, probably the most important
health effects of cannabis use are:
injury or death resulting from intoxication--for example, from a
traffic crash
respiratory disorders and ailments linked to heavy use
dependence on cannabis, arising in a small proportion of users.
By any accounting, the impact of health problem linked to
cannabis is much less than that resulting from alcohol or tobacco
use. Survey data from the US., for example, show that dependence on
nicotine among smokers is several times more prevalent than cannabis
dependence among marijuana users (Kandel et al., 1997). Moreover,
the legal drugs tobacco and alcohol account for the bulk of the
economic costs of substance use. For example, a recent Ontario study
found that annual health care costs resulting from cannabis use were
small ($8 million) when compared to those for tobacco ($1.07 billion
) and alcohol ($442 million). (Xie et al., 1996; Unpublished
analysis of economic cost date, ARF, 1997)
