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The
prohibition of cannabis, and some of the doubts about its medical
use, is based on the belief that it is harmful to health. Recent reviews
on this subject include the World Health Organisation (WHO) report
Cannabis: a health perspective and research agenda, and the Australian
National Drug Strategy report the health and psychological consequences
of cannabis use. All agree however, that acute toxicity of cannabis
is very low; no one has ever died as a direct and immediate consequence
of recreational or medical use. Official statistics show just four
deaths involving cannabis (alone), all due to vomit inhalation.
Acute
(immediate, short-term) health effects:
- A
state of euphoric intoxication, or 'high'. Usually the effect precisely
sought by the recreational user. However, people using for medical
purposes may view this as an unwanted side effect.
- Significant
lowering of the blood pressure and increased heart rate can occur.
It is for this reason that people known to suffer cardiovascular disease
may be at risk.
-
Slight impairment of cognitive & psychomotor performance, which
is significant for those operating machinery or driving. The Department
of Health see this as "the major concern (raised by recreational
use) from a public health perspective". However, the impairment
in driving ability does not seem to be drastic, when subjects are
tested in a simulator. This could be because stoned people compensate
for their impairment by taking less risks and driving more slowly,
whereas alcohol encourages people to take bigger risks and drive
more aggressively. Unfortunately, it would be very difficult to
monitor for intoxication, should the use of cannabis be permitted.
-
Short-term cognitive effects also include impaired short-term memory
and reduced attention span.
-
An
inexperienced user, or a habitual user taking a large dose, may experience
a mixture of unpleasant psychological effects (sometimes referred
to as a "whitey" due to the pale colour of the skin) including
heightened anxiety, paranoia and panic.
-
Cannabis
use may occasionally lead to a longer-lasting psychosis involving
hallucinations and delusions (lasting up to a few days). It is well
established that cannabis may lead to exacerbation of schizophrenic
illness, but there is no evidence that cannabis can cause schizophrenia
or any other mental health problems in those not already known to
suffer them. The Royal College of Psychiatrists, however, rates
the proportion of users who experience adverse mental effects as
"significant".
Chronic (long-term) health
effects:
-
Cannabis
may affect cognitive (brain) performance in the long term, especially
in heavy users. The Royal College of Psychiatrists reports that
while users show little impairment in simple short-term memory tests,
they may show notable impairment in more complex tasks. While evidence
exists that some impairment may persist after discontinuing cannabis
use, such residual effects are small, and their presence controversial.
-
"Amotivational
syndrome" in long-term users, with lack of energy and will
to work, has been suggested, although it is generally discounted
and thought to characterise nothing more than ongoing intoxication.
It may also be more of a social comment on the kind of people who
are more likely to use recreational drugs.
-
Although
there is evidence to suggest alterations in male and female sex
hormones, there is none that cannabis negatively effects fertility,
or possesses dysmorphogenic effects (chromosome interference leading
to birth defects). However, use by pregnant women may lead to shorter
pregnancy (not in a good way) and lower birth-weight babies. These
effects are probably due to inhalation of carbon monoxide in smoke
(which lowers the amount of oxygen carried to the foetus), rather
than the effects of cannabinoids. The same would be true with tobacco
smoke, which is also not recommended during pregnancy.
-
There
is little evidence that THC affects cell metabolism and DNA synthesis.
There is strong evidence however that cannabis smoke causes mutations
in cells and therefore is a potential cause of cancer. Cannabis
smoke and cigarette smoke contain many of the same carcinogenic
(cancer causing) substances. It is for this reason that many consider
the consequences of smoking as the most important long-term risk
associated with cannabis use. There are reports of an increased
incidence of throat and mouth cancers in young cannabis users. Cannabis
smoke contains higher concentrations of certain carcinogens. The
BMA estimate that smoking a spliff results in approximately a threefold
increase in the amount of tar inhaled, and retention of one third
more tar than smoking a normal cigarette. Cannabis is often smoked
mixed with tobacco, hence adding the many well-documented risks
of exposure to tobacco smoke. Add to this that many cannabis users
are already tobacco smokers, and you have a complicated task for
the researchers.
-
Heavy
cannabis use is associated with a higher incidence of respiratory
disease, such as chronic bronchitis & asthma.
Most
studies agree that on current usage patterns, alcohol and tobacco
are far more damaging to public health than cannabis, which does not
contribute to deaths, and causes only a small increase in morbidity
(levels of illness). No one, however, can predict the effect that
an increase in availability (and promotion) of cannabis would have
on these figures. It's a fairly safe bet to say that the adverse effect
on public health would increase, but it is impossible to know by how
much.
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