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HARVARD MEDICAL REPORT ON MARIJUANA
--excerpted from the Harvard Medical School Mental
Health Letter, November 1987
Although still illegal, marijuana has become a commonplace
part of the American social scene, used regularly by millions and
occasionally by millions more. A realistic view of this drug is now
more important and easier to achieve.
The use of marijuana reached a high point in the late 1970's
and early 1980's, and has been declining ever since. In a 1978
survey, 37% of high school seniors said they had smoked marijuana
in the last 30 days, and 11% said they used it daily. By 1986 the
number who said they had smoked it in the last 30 days had fallen
to 23%--lower than in 1975--and the proportion of daily users had
dropped steadily to 4%. The trend among people\ aged 18 to 25 is
similar. More people over 25 may now be using it occasionally, and
young people are still experimenting with it.
The main active ingredient of cannabis is delta-9-
tetrahydrocannabinol (THC). one of more than 60 related chemicals
found in the resin that covers the flowers and top leaves of the
cannabis (hemp) plant. Leaves and flowers can be ground up in
drinks or food, but are more often dried and smoked in a cigarette
or pipe. The pure resin, known as hashish, can also be smoked,
eaten or drunk. New breeding and cultivation techniques have raised
the THC content of marijuana smoked in the United States as much as
10 times over the last 20 years, from an average of 0.4% to 4%.
EFFECTS: The effects last two to four hours when marijuana is
smoked, and five to 12 hours when taken by mouth. Although
intoxication varies with psychological set and social setting, the
most common response is a calm, mildly euphoric state in which time
slows and sensitivity to sights, sounds and touch is enhanced.
The smoker may feel exhilaration or hilarity and notice a
rapid flow of ideas with a reduction in short-term memory. Images
sometimes appear before closed eyes;visual perception and body
image may undergo subtle changes. It is dangerous to operate
complex machinery, including automobiles, under the influence of
marijuana.
The main physiological effects of cannabis are increased
appetite a faster heartbeat, and sightly bloodshot eyes.
NEGATIVE REACTIONS: Although the increased heart rate could be
a problem for people with cardiovascular disease, dangerous
physical reactions to marijuana are almost unknown.
No human being is known to have died of an overdose. Like many
other drugs, cannabis produces a toxic delirium when taken at very
high doses, especially by mouth. The symptoms are confusion,
agitation, disorientation, loss of coordination, and often
hallucination; the delirium ends when the drug passes out of the
body. The most common disturbing reaction to marijuana is acute
anxiety, sometimes accompanied by paranoid thoughts, which may lead
to panic. The most likely victim of this reaction is an
inexperienced user inadvertently taking a high dose in an
unpleasant or unfamiliar setting. The best way to handle the
anxiety and paranoia is calming support and reassurance.
Cannabis is less potent than hallucinogenic or psychedelic
drugs and the user is better able to control its effects.
LONG TERM EFFECTS: In recent years the psychological and
physical effects of long-term use have caused the most concern.
Studies are often conflicting and permit various views of
marijuana's possible harmfulness.
Two recognized signs of addiction are tolerance and withdrawal
symptoms. These are rarely a serious problem for marijuana users:
almost no one reports an urgent need to increase the dose to
recapture the original sensation, and there is little evidence that
withdrawal ordinarily presents serious problems to users, or causes
them to go on taking the drug.
People suffering from drug dependence find that they are
constantly thinking about the drug, or intoxicated, or recovering
from its effects. The habit impairs their mental and physical
health and hurts their work, family life, and friendships. They
often know that they are using too much and repeatedly make
unsuccessful attempts to cut down or stop. Those problems seem to
occur in proportionately fewer marijuana smokers than users of
alcohol, tobacco, heroin or cocaine.
Most people who develop marijuana dependency would be would be
likely to develop other dependencies because of anxiety, depression
or feelings of inadequacy. The troubled teen who smokes cannabis
throughout the school day certainly has a problem, and excessive
use may be one symptom.
BEHAVIORAL EFFECTS: Experiments in the U.S. show no effects of
fairly heavy marijuana use on learning, perception or motivation
over periods as long as a year.
In three major studies, conducted in Jamaica, Costa Rica and
Greece, researchers compared heavy long-term cannabis users with
non-users and found no evidence of intellectual or neurological
damage, no changes in personality, and no loss of the will to work
or to participate in society.
Much attention has also been devoted to the idea that
marijuana smoking leads to use of other illicit drugs: the
"stepping stone" hypothesis. There is no convincing evidence for or
against this. What is clear is that at many times and places
marijuana has been used without these drugs, or these drugs have
been used without marijuana.
REPRODUCTION: Most recent studies on the health hazards of
marijuana concerns its long-term effects on the body. Studies have
examined the brain, the immune system, the reproductive system, and
the lungs. Suggestions of long-term damage come almost exclusively
from animal experiments and other laboratory work. Observations of
marijuana users and the Caribbean, Greek and other studies reveal
little disease or organic pathology associated with the drug. If
there were significant damage, we might expect to find a higher
rate of these diseases among young people beginning in the 1960's,
when marijuana first became popular. There is no evidence of that.
The effects of marijuana on the reproductive system are a more
complicated issue. In men, a single dose of THC lowers sperm count
and the level of testosterone and other hormones. Tolerance to this
effect apparently develops; in the Costa Rican study, marijuana
smokers and controls had the same testosterone levels. There is no
evidence that the changes in sperm count and testosterone affect
sexual performance or fertility.
In animal experiments, THC has been reported to lower levels
of female hormones and disturb the menstrual cycle. When monkeys,
rats and mice have been exposed during pregnancy to amounts of THC
equivalent to a heavy smoking human's dose, stillbirths and
decreased birth weight are sometimes reported in their offspring.
There are also reports of low birth weight, prematurity and even a
condition resembling the fetal alcohol syndrome in some children of
women who smoke marijuana heavily during pregnancy.
The significance of these reports is unclear because controls
are lacking and other circumstances make is hard to attribute
causes. To be safe, pregnant and nursing women should follow the
standard conservative recommendation to avoid all drugs, including
cannabis, that are not absolutely necessary.
LUNGS: A well-confirmed danger of long-term heavy marijuana
use is its effects on the lungs. Smoking narrows and inflames air
passages and reduces breathing capacity; damage to bronchial cells
has been observed in hashish smokers. Possible harmful effects
include bronchitis, emphysema and lung cancer. Marijuana smoke
contains the same carcinogens as tobacco smoke, usually in somewhat
higher concentrations, and is inhaled more deeply and held in the
lungs longer, which increases the danger. On the other hand, almost
no one smokes 20 marijuana cigarettes a day.
Higher THC content in cannabis may reduce the danger of
respiratory damage, because less smoke is required for the desired
effect. This is only true as long as no significant tolerance
develops and users do not try to get proportionately more intense
effect from a stronger form of the drug.
END