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The Health Effects of Marijuana on Humans
Introduction
Marijuana has been used as a drug since the beginning of
time, yet there are still many mysteries about its health
effects on humans. Marijuana, or cannabis sativa, is a
preparation of the crushed flowers and buds of female hemp
plant. The existence of the plant has been reported as
early as 1500-1200 BC. in China, and cannabis has been
described as an analgesic as early as 200 AD (Walton, 1938).
Since then, an overwhelming number of studies have attempted
to explain the physical and psychological effects of
cannabis on humans.
Physical Effects
Physically, cannabis is relatively harmless. Studies
have observed interesting results, including that it causes
structural changes in the brain, depresses male sperm
counts, causes chromosome damage, lowers testosterone
levels, and damages the lungs. Most of these claims,
however, have been unreplicated in humans or have been
contradicted by other work. This section will address each
of these reported negative side-effects.
Various studies have claimed that cannabis destroys brain
cells (Landfield et al., 1988; Haper et al., 1977; Meyers
and Heath, 1979; Heath et al., 1980). However, several
other studies found no structural or neurochemical atrophy
in the brain at all (Cabral et al., 1991; Paule et al.,
1992; Co et al., 1977; Kuehnle, 1977). Furthermore, it
should be noted that Heath's work was sharply criticized for
avoiding safeguards of bias and reporting "changes" that
occur normally in the mammalian brain (Natl. Acad. of
Sciences, Inst. Medicine, 1982).
Wu et al. (1988) found a correlation between cannabis use
and low sperm counts in human males. This is misleading
because a decrease in sperm count has not been shown to have
a negative effect on fertility and because the sperm count
returns to normal after cannabis use has stopped. (Natl.
Acad. Sciences, Inst. Medicine, 1982)
Another claim made was that cannabis causes chromosome
breakage. The primary source for this are studies that were
conducted by Dr. Gabriel Nahas in the early 1980s. Nahas
observed abnormalities in somatic (not sex) cells of rhesus
monkeys in vitro (i.e., in test tubes and petri dishes) and
then made the unjustified conclusion that these changes
would occur in human bodies in vivo (in the body). Nahas'
work was criticized by his colleagues and, in 1983, he
backed away from his own conclusions.
A widely held claim has also been that cannabis lowers
male testosterone levels (Kolodny, 1974). This theory has
been challenged by several studies (Block, 1991; Mendelson
et al., 1974; Coggins et al., 1976) that found no
correlation at all. Marijuana and Health (Natl. Acad.
Sciences, Inst. Medicine, 1982), also, after reviewing
literature at that time, concluded that "Due to conflicting
and incomplete evidence, it is not possible to conclude at
the present time whether marijuana smoking has a significant
effect upon gonadotropic and testosterone concentrations in
humans."
The most serious physical danger of using cannabis is in
smoking it. Inhaling any sort of burnt plant matter is not
very good for the lungs. Tashkin et al. (1990) reports
decreased gas exchange capacity and the existence of
particle residue in the lungs of marijuana smokers several
times greater than for tobacco smokers. Wu et al. (1988)
noted that marijuana is several times more carcinogenic than
tobacco. These findings, though, must be interpreted with
caution. In both studies, smoked marijuana was not
filtered, while smoked tobacco was. Tashkin et al. notes
that, "these differences could largely account for more than
twofold greater tar yield from marijuana than tobacco that
was measured using syringe-simulated puffs of similar volume
and duration." Smoking cannabis through a water-pipe will
filter out water soluble carcinogens and will also greatly
cool down the smoke. Furthermore, cannabis need not be
smoked: In Middle Eastern countries, it has been consumed
through teas and food for centuries, avoiding the
carcinogenicity of smoke altogether.
Despite cannabis' known negative effects to lung
function, it has never been reported to cause a single
instance of lung cancer. Tobacco, though, is expected to
kill 400,000 people this year (Glenn, 1992). If cannabis is
so much more dangerous to a user's lungs than tobacco and is
so much more carcinogenic, why aren't there stacks of
reports of cannabis-induced lung cancer? One interesting
theory is that it's because tobacco tars are significantly
radioactive, while marijuana tars aren't at all. Winters et
al. (1982) found that a pack-and-a-half-a-day smoker of
tobacco is exposed to 8000 mrem of radiation a year, equal
to the dose of 300 chest x-rays. A more recent study
indicates that a pack-and-a-half-a-day smoker receives 16000
mrem of radiation more than a non-smoker, annually (NCRP
Report #95, 1987). It could also be noted that the mere
contents of carcinogenic chemicals doesn't necessarily
indicate an extreme health hazard. For example, roasted
coffee contains 800 volatile chemicals, of which only 21
have been tested on rodents, and of those, 16 were
carcinogenic (Ames, 1990). Coffee has never been considered
a great cancer-causing substance, though.
Cannabis has also been known for its many therapeutic
uses, including the treatment of open angle glaucoma,
asthma, and the nausea associated with chemotherapy. It has
also been described as a tumor retardant, an antibiotic, a
sleep-inducer, and a muscle relaxant (Cohen, 1980).
Psychological Effects
The psychological effects of cannabis use have been
described quite many years before the physical effects, yet
are as accurate today as they were 100 years ago. Following
is an early account of its intoxicating properties made by
Dr. John Bell in 1857:
"I had taken the drug with great skepticism
as to its reputed action, or at any rate with the
opinion that it was grossly exaggerated, and I
accordingly made up my mind not to be 'caught
napping' in this way again, and to keep a careful
watch over my thoughts. But while enforcing this
resolution as I supposed, I found myself, to my
own astonishment, waking from a reverie longer and
more profound than any previous. From skepticism,
to the fullest belief of all I had read on the
subject, was but a step. Its effects so far
surpassed anything which words can convey, that I
began to think I was on the verge of narcotic
poisoning; yet, strange to say, there was not the
slightest feeling of inquietude on that account.
I resolved to walk into the street. While rising
from the chair, another lucid interval showed that
another dream had come and gone. While passing
through the door, I was aware of having wandered
again, but how or when I had permitted myself to
fall into the reverie I was perfectly unconscious,
and knew only that it seemed to have lasted an
interminable length of time." (Bell, 1857)
The user of cannabis feels the onset of the "high"
between 7 seconds (when smoking) and up to 30 minutes (after
eating). This involves a relaxed and peaceful, yet
sometimes euphoric state of mind. At high doses, it can
cause hallucinations. The effects last from 2 to 4 hours
after the drug is ingested, and it usually leaves the user
in a relaxed state for several hours after the high. One of
the main intoxicating properties is that short term memory
is inhibited for the duration of the high. Thoughts may
seem unclear, and it might be difficult for a user to
concentrate on logical-complicated concepts like
mathematics.
Long-term effects have been argued for many years. There
are claims of an "amotivational syndrome" where users are
said to withdraw from society and lose ambition. In
reviewing evidence for and against the theory of this
"syndrome," however, Marijuana and Health (Nat. Acad.
Sciences, Inst. Medicine, 1982) concluded that:
"Such symptoms have been known to occur in the
absence of marijuana. Even if there is an
association between this syndrome and the use of
marijuana, that does not prove that marijuana
causes the syndrome. Many troubled individuals
seek an 'escape' into use of drugs; thus, frequent
use of marijuana may become one more in a series
of counterproductive behaviors for these unhappy
people."
Other studies have found another interesting correlation:
Shedler et al. (1990) reported these results in a
longitudinal survey of adolescents:
"Adolescents who engaged in some drug
experimentation (primarily with marijuana) were
the best adjusted in the sample. Adolescents who
used drugs frequently were maladjusted, showing
distinct personality syndrome marked by
interpersonal alienation, poor impulse control,
and manifest emotional distress. Adolescents who,
by age 18, had never experimented with any drug
were relatively anxious, emotionally constricted,
and lacking in social skills."
Among other findings, Utah Power and Light spent $215.00 per
year less on health insurance benefits for drug users than
on the control group, and employees who tested positive for
cannabis at Georgia Power Co. had a higher promotion rate
than the company average, and were absent 30 percent less
(Morris, 1991).
Conclusion
Whether cannabis use causes permanent physical or
psychological changes in its users is still under question.
The most serious concern is its effects on the pulmonary
system, yet, studies have often used poor controls (i.e., no
filtration) and their results can mislead an uncareful
reader. Smoking the drug with a different apparatus or
ingesting it without smoking at all could greatly effect the
results of these studies.
The acute psychological effects of cannabis that cause
its intoxicating properties are no mystery, as any user can
report. Long term effects of cannabis use could possibly
lead to the so-called "amotivational syndrome," but
scientific evidence is lacking.
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