The current consensus is well stated in the 20th annual report of the California Research Advisory Panel (1990), which recommended that personal use and cultivation of marijuana be legalized: "An objective consideration of marijuana shows that it is respo nsible for less damage to society and the individual than are alcohol and cigarettes."
Myth: Marijuana is harmless
Just as most experts agree that occasional or moderate use of marijuana is innocuous, they also agree that excessive use can be harmful. Research shows that the two major risks of excessive marijuana use are:
Marijuana and Smoking:A recent survey by the Kaiser Permanente Center found that daily marijuana-only smokers have a 19% higher rate of respiratory complaints than non-smokers.(1)
These findings were not unexpected, since it has long been known that, aside from its
psychoactive ingredients, marijuana smoke contains virtually the same toxic gases and
carcinogenic tars as tobacco. Human studies have found that pot smokers suffer similar
kinds of respiratory damage as tobacco smokers, putting them at greater risk of bronchitis,
sore throat, respiratory inflammation and infections.(2)
Although there has not been enough epidemiological work to settle the matter definitively, it is widely suspected that marijuana smoking causes cancer. Studies have found apparently pre-cancerous cell changes in pot smokers.(3) Some cancer specialists have reported a higher-than-expected incidence of throat, neck and tongue cancer in younger, marijuana-only smokers.(4) A couple of cases have been fatal. While it has not been conclusively proven that marijuana smoking causes lung cancer, the evidence is highly suggestive. According to Dr. Donald Tashkin of UCLA, the leading expert on marijuana smoking:(5)"Although more information is certainly needed, sufficient data have already been accumulated concerning the health effects of marijuana to warrant counseling by physicians against the smoking of marijuana as an important hazard to health." Fortunately, the hazards of marijuana smoking can be reduced by various strategies:
Myth: One joint equals one pack of (or 16, or maybe
just 4) cigarettes
Some critics exaggerate the dangers of marijuana smoking by fallaciously citing a study by
Dr. Tashkin which found that daily pot smokers experienced a "mild but significant"
increase in airflow resistance in the large airways greater than that seen in persons
smoking 16 cigarettes per day.(7) What they ignore is that the same
study examined other, more important aspects of lung health, in which marijuana smokers
did much better than tobacco smokers. Dr. Tashkin himself disavows the notion that one
joint equals 16 cigarettes. A more widely accepted estimate is that marijuana smokers
consume four times as much carcinogenic tar as cigarettes smokers per weight smoked.
(8) This does not necessarily mean that one joint equals four cigarettes,
since joints usually weigh less. In fact, the average joint has been estimated to contain
0.4 grams of pot, a bit less than one-half the weight of a cigarette,
making one joint equal to two cigarettes (actually, joint sizes range from cigar-sized spliffs
smoked by Rastas, to very fine sinsemilla joints weighing as little as 0.2 grams).
It should be noted that there is no exact equivalency between tobacco and marijuana smoking,
because they affect different parts of the respiratory tract differently:
whereas tobacco tends to penetrate to the smaller, peripheral passageways of the lungs,
pot tends to concentrate on the larger, central passageways.(9)
One consequence of this is that pot, unlike tobacco, does not appear to cause emphysema.
References on Marijuana and Smoking: Donald Tashkin, Is Frequent Marijuana
Smoking Hazardous To Health?, Western Journal of Medicine 158 #6: 635-7; June 1993;
Research Findings on Smoking of Abused Substances, ed. C. Nora Chiang and Richard L. Hawks,
NIDA Research Monograph 99 (National Institute on Drug Abuse, Rockville, MD 1990); NAS
Report,op. cit.; California NORML, Health Tips for Marijuana Smokers.
References on Accidents and Drug Testing: Alcohol, Drugs and Driving: Abstracts and
Reviews Vol. 2 #3-4 (Brain Information Service, UCLA 1986); Dale Gieringer,
Marijuana, Driving, and Accident Safety, Journal of Psychoactive Drugs 20
(1): 93-101 (Jan.-Mar 1988); Dr. John Morgan, Impaired Statistics and the Unimpaired Worker,
Drug Policy Letter 1(2): May/June 1989, and The "scientific" justification for drug urine
testing, The University of Kansas Law Review 36: 683-97 (1988); John Horgan,
Test Negative: A look at the evidence justifying illicit-drug tests, Scientific
American, March 1990 pp. 18-22, and Postal Mortem, Scientific American, Feb. 1991
pp. 22-3; Dale Gieringer, Urinalysis or Uromancy? in Strategies for Change: New
Directions in Drug Policy (Drug Policy Foundation, 1992).
Contrary to popular myth, greater potency is not necessarily more dangerous, due to the fact
that users tend to adjust (or "self-titrate") their dose according to potency. Thus, good
quality sinsemilla is actually healthier for the lungs because it reduces the amount of
smoke one needs to inhale to get high.
Less is known about the effects of cannabis on human females. Some animal studies suggest that
pot might temporarily lower fertility or increase the risk of fetal loss, but this evidence is
of dubious relevance to humans.(1) One human study suggested that pot
may mildly disrupt ovulation. It is possible that adolescents are peculiarly vulnerable to
hormonal disruptions from pot. However, not a single case of impaired fertility has ever been
observed in humans of either sex.
One thing THC does do is to increase pulse rates for about an hour. This is not generally
harmful, since exercise does the same thing, but it may cause problems to people with
pre-existing heart disease. Chronic users may develop a tolerance to this and other
cardiovascular reactions.
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.(9) 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.(10) 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 devices(11).
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.(12) Epidemiological studies
have found no relation between use of marijuana or other drugs and development of
AIDS.(13)
Myth: Prohibition reduces the harmfulness of pot
smoking
Whatever the risks of pot smoking, the current laws make matters worse in
several respects:
Unlike the government, NORML is interested in reducing the dangers of pot smoking;
California NORML and MAPS (the Multidisciplinary Association for Psychedelic Studies)
are currently researching the use of waterpipes and other advanced smoke reduction
technology.Myth: No one has ever died from using marijuana
The Kaiser study also found that daily pot users have a 30% higher risk of injuries,
presumably from accidents. These figures are significant, though not as high as comparable
risks for heavy drinkers or tobacco addicts. That pot can cause accidents is scarcely
surprising, since marijuana has been shown to degrade short-term memory, concentration,
judgment, and coordination at complex tasks including driving.(1)
There have been numerous reports of pot-related accidents --- some of them fatal, belying
the attractive myth that no one has ever died from marijuana. One survey of 1023 emergency
room trauma patients in Baltimore found that fully 34.7% were under the influence of
marijuana, more even than alcohol (33.5%); half of these (16.5%) used both pot and alcohol
in combination.(2) This is perhaps the most troublesome research
ever reported about marijuana; as we shall see, other accident studies have generally
found pot to be less dangerous than alcohol. Nonetheless, it is important to be informed
on all sides of the issue. Pot smokers should be aware that accidents are the number
one hazard of moderate pot use. In addition, of course, the psychoactive effects of
cannabis can have many other adverse effects on performance, school work, and productivity.Myth: Marijuana is a major road safety hazard
A growing body of research indicates that marijuana is on balance less of a road hazard than
alcohol. Various surveys have found that half or more of fatal drivers have alcohol in their
blood, as opposed to 7 - 20% with THC, the major psychoactive component of marijuana (a
condition usually indicative of having smoked within the past 2-4 hours).(3)
The same studies show that some 70 - 90% of those who are THC-positive also have alcohol
in their blood. It therefore appears that marijuana by itself is a minor road safety hazard,
though the combination of pot and alcohol is not. Some research has even suggested that
low doses of marijuana may sometimes improve driving performance, though this is probably
not true in most cases.(4) Two major new studies by the National Highway
Transportation Safety Administration have confirmed marijuana's relative safety compared to
alcohol. The first, the most comprehensive drug accident study to date, surveyed blood samples
from 1882 drivers killed in car, truck and motorchycle accidents in seven states
during 1990-91.(5) Alcohol was found in 51.5% of specimens, as against
17.8% for all other drugs combined. Marijuana, the second most common drug, appeared in just
6.7%. Two-thirds of the marijuana-using drivers also had alcohol. The report concluded that
alcohol was by far the dominant drug-related problem in accidents. It went on to
analyze the responsibility of drivers for the accidents they were involved in. It found that
drivers who used alcohol were especially culpable in fatal accidents, and even more so when
they combined it with marijuana or other drugs. However, those who used marijuana alone
appeared to be if anything less culpable than non-drug users (though the data were insufficient
to be statistically conclusive). The report concluded, "There was no indication that marijuana
by itself was a cause of fatal accidents." (It must be emphasized that this is not the case
when marijuana is combined with alcohol or other drugs). The second NHTSA study,
Marijuana and Actual Driving Performance, concluded that the adverse effects of
cannabis on driving appear "relatively small" and are less than those of drunken driving.
(6) The study, conducted in the Netherlands, examined the performance of
drivers in actual freeway and urban driving situations at various doses of marijuana. It
found that marijuana produces a moderate, dose-related decrement in road tracking ability, but
is "not profoundly impairing" and "in no way unusual compared to many medicinal drugs." It
found that marijuana's effects at the higher doses preferred by smokers never exceed those
of alcohol at blood concentrations of .08%, the minimum level for legal intoxication in
stricter states such as California. The study found that unlike alcohol, which encourages
risky driving, marijuana appears to produce greater caution, apparently because users are
more aware of their state and able to compensate for it (similar results have been reported
by other researchers as well.(7)) It should be noted that these results
may not apply to non-driving related situations, where forgetfulness or inattention can be
more important than speed (this might explain the discrepancy in the Baltimore hospital
study, which looked at accidents of all kinds). The NHTSA study also warned that marijuana
could also be quite dangerous in emergency situations that put high demands on driving
skills.Myth: Marijuana prohibition improves public safety
There is no evidence that the prohibition of marijuana reduces the net social risk of
accidents. On the contrary, recent studies suggest that marijuana may actually be beneficial
in that it substitutes for alcohol and other, more dangerous drugs. Research by Karyn Model
found that states with marijuana decrim had lower overall drug abuse rates than others;
another study by Frank Chaloupka found decrim states have lower accident rates too.
(8) In Alaska, accident rates held constant or declined following the
legalization of personal use of marijuana.(9) In Holland, authorities
believe that cannabis has contributed to an overall decline in opiate abuse. Recent
government statistics showed that the highest rates of cocaine abuse in the West were in
Nevada and Arizona, the states with the toughest marijuana laws.Myth: Drug urinalysis improves workplace safety
There has never been a single, controlled scientific study showing drug urinalysis improves
workplace safety. Claims that drug testing works are based on dubious anecdotal reports or
the mere observation of a declining rate of drug positives in the working population, which
has nothing to do with job performance. Such scientific studies as have been conducted
have found little difference between the performance of drug-urine-positive workers
and others. The largest survey to date, covering 4,396 postal workers nationwide, found no
difference in accident records between workers who tested positive on pre-employment drug
screens and those who did not.(10) The study did find that drug-positive
workers had a 50% higher rate of absenteeism and dismissals; put another way, however, drug
users had a 93.4% attendance record (versus 95.8% for non-users) and fully 85% kept their
jobs for a year (versus 89.5% for non-users)! An economic analysis of postal workers in
Boston concluded that the net savings of drug testing were marginal, and that there could be
many situations where it is not cost-effective.(11) Another survey of
health workers in Georgia found no difference in job performance between drug-positive and
drug-negative workers.(12)Myth: Random urinalysis is needed in safety-sensitive
transportation jobs
Government rules mandating random drug testing were promulgated without any prior statistical
evidence that illicit drugs constituted an inordinate safety hazard. Not a single commercial
passenger airline accident has ever been attributed to marijuana (or, for that matter,
alcohol) abuse.(1) Drug tests on rail workers found no elevated
incidence of drug use among workers involved in accidents.(2)
Random drug testing of transportation workers was enacted as a hysterical reaction to a
single 1987 train collision, in which 16 Amtrak passengers were killed by a Conrail train
that failed to stop. The engineer and brakeman of the Conrail train at fault were found
to have recently smoked marijuana, though it was never firmly proven that marijuana caused
the accident. The Conrail engineer had an extensive record of speeding and drunken driving
offenses and was known by management to have drinking problems. Critical safety equipment
that would have averted the accident was missing or disabled. A subsequent investigation
by the National Transportation Safety Board recommended that Conrail improve both its
management and equipment, but did not recommend random testing. Nonetheless, Congress
responded by mandating random drug testing on the entire transportation industry, from
airline flight attendants to gas pipeline workers.Myth: A single joint has effects that linger for days
and weeks
While it is true that THC and other cannabinoids are fat-soluble and linger in the body for
prolonged periods, they do not normally affect behavior beyond a few hours except in chronic
users. Most impairment studies have found that the adverse effects of acute marijuana use
wear off in 2-6 hours, commonly faster than alcohol.(3) The one notable
exception was a pair of flight simulator studies by Leirer, Yesavage, and Morrow, which
reported effects on flight simulator performance up to 24 hours later.(4)
The differences, described by Leirer as "very subtle" and "very marginal," were less than
those due to pilot age. Another flight simulator study by the same group failed to find any
effects beyond 4 hours.(5) Similar "hangover" effects have been noted for
alcohol.(6) Chronic users may experience more prolonged effects due
to a build-up of cannabinoids in the tissues. Some heavy users have reported feeling effects
weeks or even months after stopping. However, there is no evidence that these are detrimental
to safety.Myth: Pot is ten times more potent and dangerous now
than in the 1960's
The notion that pot has increased dramatically in potency is a DEA myth based on biased
government data, as shown in a recent NORML report by Dr. John Morgan.(7)
Samples of pot from the early '70s came from stale, low-potency Mexican "kilobricks" left in
police lockers, whose potency had deteriorated to sub-smokable levels of less than 0.5%. These
were compared to later samples of decent-quality domestic marijuana, making it appear
that potency had skyrocketed. A careful examination of the government's data show that
average marijuana potency increased modestly by a factor of two or so during the seventies,
and has been more or less constant ever since.In fact, there is nothing new about
high-potency pot. During the sixties, it was available in premium varieties such as
Acapulco Gold, Panama Red, etc. , as well as in the form of hashish and hash oil, which
were every bit as strong as today's sinsemilla, but were ignored in government potency
statistics. While the average potency of domestic pot did increase with the development
of sinsemilla in the seventies, the range of potencies available has remained virtually
unchanged since the last century, when extremely potent tonics were sold over the counter
in pharmacies. In Holland, high-powered hashish and sinsemilla are currently sold in
coffee shops with no evident problems.Myth: Pot kills brain cells
Government experts now admit that pot doesn't kill brain cells.(8)
This myth came from a handful of animal experiments in which structural changes (not actual
cell death, as is often alleged) were observed in brain cells of animals exposed to high
doses of pot. Many critics still cite the notorious monkey studies of Dr. Robert G. Heath,
which purported to find brain damage in three monkeys that had been heavily dosed with
cannabis.(9) This work was never replicated and has since been
discredited by a pair of better controlled, much larger monkey studies, one by Dr.
William Slikker of the National Center for Toxicological Research(10)
and the other by Charles Rebert and Gordon Pryor of SRI International.(11)
Neither found any evidence of physical alteration in the brains of monkeys exposed to
daily doses of pot for up to a year. Human studies of heavy users in Jamaica and Costa Rica
found no evidence of abnormalities in brain physiology.(12) Even though
there is no evidence that pot causes permanent brain damage, users should be aware that
persistent deficits in short-term memory have been noted in chronic, heavy marijuana smokers
after 6 to 12 weeks of abstinence.(13) It is worth noting that other
drugs, including alcohol, are known to cause brain damage.Myth: Marijuana causes sterility and lowers
testosterone
Government experts also concede that pot has no permanent effect on the male or
female reproductive systems.(14) A few studies have suggested that
heavy marijuana use may have a reversible, suppressive effect on male testicular
function.(15) A recent study by Dr. Robert Block has refuted earlier
research suggesting that pot lowers testosterone or other sex hormones in men
or women.(16) In contrast, heavy alcohol drinking is known to lower
testosterone levels and cause impotence. A couple of lab studies indicated that very
heavy marijuana smoking might lower sperm counts. However, surveys of chronic smokers have
turned up no indication of infertility or other abnormalities.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.(2) A recent study by Dr. Susan Astley at the University of Washington refuted an
earlier work suggesting that cannabis might cause fetal alcohol syndrome.(3)
Although some research has found that prenatal cannabis use is associated with slightly
reduced average birth weight and length,(4) 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.(5) 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.(6) 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.(7) 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.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:(8)
"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."Myth: Marijuana causes chromosome and cell damage
According to the NAS,(14) "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 we have seen, there is
evidence that cannabis may substitute for alcohol and other "hard" drugs. A recent 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.(15) Dr. Morgan noted
a similar phenomenon in California, where cocaine use soared in the wake of the CAMP
helicopter eradication campaign.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.
National Organization for the Reform of Marijuana Laws
1001 Connecticut Avenue NW, Suite 1010
Washington, D.C. 20036
or call 1-900-97-NORML ($2.95/min.; must be 18 years of age)