Myth: Marijuana Causes Birth Defects
While experts generally recommend against
any drug use during pregnancy, marijuana has little evidence
implicating it in fetal harm, unlike alcohol, cocaine or tobacco.
Epidemiological studies have found no evident link between
prenatal use of marijuana and birth defects in humans[40]
A recent study by Dr. Susan Astley at the University of Washington
refuted an earlier work suggesting that cannabis might cause fetal
alcohol syndrome[41]
Although some research has found that
prenatal cannabis use is associated with slightly reduced average
birth weight and length[42] these studies have
been open to methodological criticism. More recently, a
well-controlled study found that cannabis use had a positive
impact on birthweight during the third trimester of pregnancy with
no adverse behavioral consequences[43] The
same study found a slight reduction in birth length with pot use
in the first two months of pregnancy. Another study of Jamaican
women who had smoked pot throughout pregnancy found that their
babies registered higher on developmental scores at the age of 30
days, while experiencing no significant effects on birthweight or
length[44]
While cannabis use is not recommended in
pregnancy, it may be of medical value to some women in treating
morning sickness or easing childbirth.
Myth: Pot Causes High Blood Pressure
According to the NAS, the effects of
marijuana on blood pressure are complex, depending on dose,
administration, and posture[45] Marijuana
often produces a temporary, "moderate" increase in blood
pressure immediately after ingestion; however, heavy chronic doses
may slightly depress blood pressure instead. One common reaction
is to cause decreased blood pressure while standing and increased
blood pressure while lying down, causing people to faint if they
stand up too quickly. There is no evidence that pot use causes
persisting hypertension or heart disease; some users even claim
that it helps them control hypertension by reducing stress.
One thing THC does do is to increase pulse
rates for about an hour, a condition known as tachycardia. This is
not generally harmful and may even be beneficial since exercise
does the same thing. However, just like hard exercise, pot use may
precipitate heart attacks in patients with pre-existing heart
disease. A study by Dr. Murray Mittleman found that users face an
elevated risk of heart attack within an hour of pot smoking,
similar to the risk from physical exercise or having sex [45A].
Chronic users may develop a tolerance to tachycardia and other
cardiovascular reactions.
Myth: Marijuana Damages the Immune System
A variety of studies indicate that THC and
other cannabinoids may exercise mild, reversible immuno-suppressive
effects by inhibiting the activity of immune system cells know as
lymphocytes (T- and B-cells) and macrophages. It is dubious
whether these effects are of import to human health, since they
are based mainly on theoretical laboratory and animal studies.
According to a review by Dr. Leo Hollister[46]
"The evidence [on immune suppression] has been contradictory
and is more supportive of some degree of immunosuppression only
when one considers in vitro studies. These have been seriously
flawed by the very high concentrations of drug used to produce
immunosuppression. The closer that experimental studies have been
to actual clinical situations, the less compelling has been the
evidence."
The immune suppression issue was first
raised in research by the notorious cannabophobe Dr. Gabriel Nahas,
but a flurry of research by the Reagan administration failed to
find anything alarming. The recent discovery of a cannabinoid
receptor inside rat spleens, where immune cells reside, raises the
likelihood that cannabinoids do exert some sort of influence on
the immune system[47] It has even been
suggested that these effects might be beneficial for patients with
auto-immune diseases such as multiple sclerosis. Nevertheless, not
a single case of marijuana-induced immune deficiency has ever been
clinically or epidemiologically detected in humans.
One exception is the lungs, where chronic
pots smokers have been shown to suffer damage to the immune cells
known as alveolar macrophages and other defense mechanisms[48]
It is unclear how much of this damage is due to THC, as opposed to
all of the other toxins that occur in smoke , many of which can be
filtered out by waterpipes and other device[49].
There is no reason to think marijuana is
dangerous to AIDS patients. On the contrary, many AIDS patients
report that marijuana helps avert the deadly "wasting
syndrome" by stimulating appetite and reducing nausea.
Cannabinoids do not actually damage the T-cells, which are
depleted in HIV patients: one study even found that marijuana
exposure increased T-cell counts in subjects (not AIDS patients)
whose T-cell counts had been low[50]
Epidemiological studies have found no relation between use of
marijuana or other drugs and development of AIDS[51]
Myth: Marijuana Causes Chromosome and Cell
Damage
According to the NAS[52]
"Studies suggesting that marijuana probably does not break
chromosomes are fairly conclusive." Cannabinoids in
themselves are neither mutagenic nor carcinogenic, though the tars
produced by marijuana combustion are. Some laboratory studies have
suggested that high dosages of THC might interfere with cell
replication and produce abnormal numbers of chromosomes; however,
there is no evidence of such damage in realistic situations.
Myth: Marijuana Leads to Harder Drugs
There is no scientific evidence for the
theory that marijuana is a "gateway" drug. The
cannabis-using cultures in Asia, the Middle East, Africa and Latin
America show no propensity for other drugs. The gateway theory
took hold in the sixties, when marijuana became the leading new
recreational drug. It was refuted by events in the eighties, when
cocaine abuse exploded at the same time marijuana use declined.
As shown above, there is evidence that
cannabis may substitute for alcohol and other "hard"
drugs. A survey by Dr. Patricia Morgan of the University of
California at Berekeley found that a significant number of pot
smokers and dealers switched to methamphetamine "ice"
when Hawaii's marijuana eradication program created a shortage of
pot[53] Dr. Morgan noted a similar phenomenon
in California, where cocaine use soared in the wake of the CAMP
helicopter eradication campaign. In its report "Marijuana and
Medicine," the National Institute of Medicine found no
scientific evidence for the gateway theory[54].
The one way in which marijuana does lead to
other drugs is through its illegality: persons who deal in
marijuana are likely to deal in other illicit drugs as well.
MYTH: Marijuana Is a Major Cause of
Schizophrenia & Psychosis
Some studies have indicated that marijuana
may be a risk factor in schizophrenia, psychosis, or other mental
illnesses. For example, a study of Swedish military personnel
found that chronic marijuana users were twice as likely to be
schizophrenic [55]. However, no increase in
the rate of schizophrenia or psychosis has been detected in those
parts of the world where cannabis use has increased greatly in
recent decades. It therefore appears that cannabis does not
increase the incidence of such problems in the general population,
as concluded by the New Zealand Parliamentary Committee [56].
On the other hand, several studies have
found that marijuana use may precipitate earlier onset of
schizophrenia or aggravate its symptoms in those already so
predisposed. [57] However, the effects of
cannabis on schizophrenics are not necessarily detrimental.
Cannabis has also been observed to mitigate symptoms in many
patients. [58] It may therefore be that the
purported link between marijuana use and schizophrenia is due to
self-medication.
In general, the evidence regarding cannabis
and schizophrenia / psychosis is conflicting, so caution is
advisable. Persons with psychotic tendencies should consult their
physicians before using cannabis.
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