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Myths and Facts About Marijuana
This collection of myths and facts is based on the book Marijuana Myths, Marijuana Facts: A Review of the Scientific Evidence . A decade after the book was published, the latest scientific evidence continues to support the original findings.
Top Five Marijuana Myths
Myth: Marijuana Can Cause Permanent Mental Illness.
Among adolescents, even occasional marijuana use may cause
psychological damage. During intoxication, marijuana users become
irrational and often behave erratically.
Fact: There is no convincing scientific evidence
that marijuana causes psychological damage or mental illness in either
teenagers or adults. Some marijuana users experience psychological
distress following marijuana ingestion, which may include feelings of
panic, anxiety, and paranoia. Such experiences can be frightening, but
the effects are temporary. With very large doses, marijuana can cause
temporary toxic psychosis. This occurs rarely, and almost always when
marijuana is eaten rather than smoked. Marijuana does not cause
profound changes in people's behavior.
Weiser and Noy. “Interpreting the association between cannabis use and increased risk of schizophrenia.” Dialogues in Clincal Neuroscience 1(2005): 81-85.
"Cannabis use will impair but not damage mental health." London Telegraph. 23 January 2006.
Degenhardt, Louisa, Wayne Hall and Michael Lynskey. “Testing
hypotheses about the relationship between cannabis use and psychosis,” Drug and Alcohol Dependence 71 (2003): 42-4.
Myth: Marijuana is Highly Addictive.
Long term marijuana users experience physical dependence and
withdrawal, and often need professional drug treatment to break their
Fact: Most people who smoke marijuana smoke it only
occasionally. A small minority of Americans - less than 1 percent -
smoke marijuana on a daily basis. An even smaller minority develop a
dependence on marijuana. Some people who smoke marijuana heavily and
frequently stop without difficulty. Others seek help from drug
treatment professionals. Marijuana does not cause physical dependence.
If people experience withdrawal symptoms at all, they are remarkably
Johnson, L.D., et al. “National Survey Results on Drug Use from
the Monitoring the Future Study, 1975-1994, Volume II: College Students
and Young Adults.” Rockville, MD: U.S. Department of Health and Human
Kandel, D.B., et al. “Prevalence and demographic correlates of
symptoms of dependence on cigarettes, alcohol, marijuana and cocaine in
the U.S. population.” Drug and Alcohol Dependence 44 (1997):11-29.
Myth: Marijuana Is More Potent Today Than In
The Past. Adults who used marijuana in the 1960s and 1970s fail to
realize that when today's youth use marijuana they are using a much
more dangerous drug.
Fact: When today's youth use marijuana, they are
using the same drug used by youth in the 1960s and 1970s. A small
number of low-THC samples seized by the Drug Enforcement Administration
are used to calculate a dramatic increase in potency. However, these
samples were not representative of the marijuana generally available to
users during this era. Potency data from the early 1980s to the present
are more reliable, and they show no increase in the average THC content
of marijuana. Even if marijuana potency were to increase, it would not
necessarily make the drug more dangerous. Marijuana that varies quite
substantially in potency produces similar psychoactive effects.
King LA, Carpentier C, Griffiths P. “Cannabis potency in Europe.” Addiction. 2005 Jul; 100(7):884-6
Henneberger, Melinda. "Pot Surges Back, But It’s, Like, a Whole New World." New York Times 6 February 1994: E18.
Drug Enforcement Administration. U.S. Drug Threat Assessment, 1993. Washington, DC: U.S. Department of Justice, 1993.
Kleiman, Mark A.R. Marijuana: Costs of Abuse, Costs of Control. Westport: Greenwood Press, 1989. 29.
Myth: Marijuana Offenses Are Not Severely Punished.
Few marijuana law violators are arrested and hardly anyone goes to
prison. This lenient treatment is responsible for marijuana continued
availability and use.
Fact: Marijuana arrests in the United States
doubled between 1991 and 1995. In 1995, more than one-half-million
people were arrested for marijuana offenses. Eighty-six percent of them
were arrested for marijuana possession. Tens of thousands of people are
now in prison or marijuana offenses. An even greater number are
punished with probation, fines, and civil sanctions, including having
their property seized, their driver's license revoked, and their
employment terminated. Despite these civil and criminal sanctions,
marijuana continues to be readily available and widely used.
Myth: Marijuana is More Damaging to the Lungs Than Tobacco. Marijuana smokers are at a high risk of developing lung cancer, bronchitis, and emphysema.
Fact: Moderate smoking of marijuana
appears to pose minimal danger to the lungs. Like tobacco smoke,
marijuana smoke contains a number of irritants and carcinogens. But
marijuana users typically smoke much less often than tobacco smokers,
and over time, inhale much less smoke. As a result, the risk of serious
lung damage should be lower in marijuana smokers. There have been no
reports of lung cancer related solely to marijuana, and in a large
study presented to the American Thoracic Society in 2006, even heavy
users of smoked marijuana were found not to have any increased risk of
lung cancer. Unlike heavy tobacco smokers, heavy marijuana smokers
exhibit no obstruction of the lung's small airway. That indicates that
people will not develop emphysema from smoking marijuana.
Inaba, Darryl S. and William E. Cohen. Uppers, Downers, All-Arounders: Physical and Mental Effects of Psychoactive Drugs. 2nd ed. Ashland: CNS Productions, 1995. 174.
More Marijuana Myths
Myth: Marijuana Has No Medicinal Value.
Safer, more effective drugs are available. They include a synthetic
version of THC, marijuana's primary active ingredient, which is
marketed in the United States under the name Marinol.
Fact: Marijuana has been shown to be effective in
reducing the nausea induced by cancer chemotherapy, stimulating
appetite in AIDS patients, and reducing intraocular pressure in people
with glaucoma. There is also appreciable evidence that marijuana
reduces muscle spasticity in patients with neurological disorders. A
synthetic capsule is available by prescription, but it is not as
effective as smoked marijuana for many patients. Pure THC may also
produce more unpleasant psychoactive side effects than smoked
marijuana. Many people use marijuana as a medicine today, despite its
illegality. In doing so, they risk arrest and imprisonment.
Myth: Marijuana is a Gateway Drug.
Even if marijuana itself causes minimal harm, it is a dangerous
substance because it leads to the use of "harder drugs" like heroin,
LSD, and cocaine.
Fact: Marijuana does not cause people to use hard
drugs. What the gateway theory presents as a causal explanation is a
statistic association between common and uncommon drugs, an association
that changes over time as different drugs increase and decrease in
prevalence. Marijuana is the most popular illegal drug in the United
States today. Therefore, people who have used less popular drugs such
as heroin, cocaine, and LSD, are likely to have also used marijuana.
Most marijuana users never use any other illegal drug. Indeed, for the
large majority of people, marijuana is a terminus rather than a gateway
D.B. Kandel and M. Davies, “Progression to Regular Marijuana Involvement: Phenomenology and Risk Factors for Near-Daily Use,” Vulnerability to Drug Abuse, Eds. M. Glantz and R. Pickens. Washington, D.C.: American Psychological Association, 1992: 211-253.
Myth: Marijuana's Harms Have Been Proved Scientifically.
In the 1960s and 1970s, many people believed that marijuana was
harmless. Today we know that marijuana is much more dangerous than
Fact: In 1972, after reviewing the scientific
evidence, the National Commission on Marihuana and Drug Abuse concluded
that while marijuana was not entirely safe, its dangers had been
grossly overstated. Since then, researchers have conducted thousands of
studies of humans, animals, and cell cultures. None reveal any findings
dramatically different from those described by the National Commission
in 1972. In 1995, based on thirty years of scientific research editors
of the British medical journal Lancet concluded that "the smoking of
cannabis, even long term, is not harmful to health."
Myth: Marijuana Causes an Amotivational Syndrome.
Marijuana makes users passive, apathetic, and uninterested in the
future. Students who use marijuana become underachievers and workers
who use marijuana become unproductive.
Fact: For twenty-five years, researchers have
searched for a marijuana-induced amotivational syndrome and have failed
to find it. People who are intoxicated constantly, regardless of the
drug, are unlikely to be productive members of society. There is
nothing about marijuana specifically that causes people to lose their
drive and ambition. In laboratory studies, subjects given high doses of
marijuana for several days or even several weeks exhibit no decrease in
work motivation or productivity. Among working adults, marijuana users
tend to earn higher wages than non-users. College students who use
marijuana have the same grades as nonusers. Among high school students,
heavy use is associated with school failure, but school failure usually
Himmelstein, J.L. The Strange Career of Marihuana: Politics and Ideology of Drug Control in America. Westport, CT: Greenwood Press, 1983.
Mellinger, G.D. et al. “Drug Use, Academic Performance, and Career Indecision: Longitudinal Data in Search of a Model.” Longitudinal Research on Drug Use: Empirical Findings and Methodological Issues. Ed. D.B. Kandel. Washington, DC: American Psychological Association, 1978. 157-177.
Pope, H.G. et al., “Drug Use and Life Style Among College Undergraduates in 1989: A Comparison With 1969 and 1978,” American Journal of Psychiatry 147 (1990): 998-1001.
Myth: Marijuana Policy in the Netherlands is a Failure.
Dutch law, which allows marijuana to be bought, sold, and used openly,
has resulted in increasing rates of marijuana use, particularly in
Fact: The Netherlands' drug policy is the most
nonpunitive in Europe. For more than twenty years, Dutch citizens over
age eighteen have been permitted to buy and use cannabis (marijuana and
hashish) in government-regulated coffee shops. This policy has not
resulted in dramatically escalating cannabis use. For most age groups,
rates of marijuana use in the Netherlands are similar to those in the
United States. However, for young adolescents, rates of marijuana use
are lower in the Netherlands than in the United States. The Dutch
people overwhelmingly approve of current cannabis policy which seeks to
normalize rather than dramatize cannabis use. The Dutch government
occasionally revises existing policy, but it remains committed to
Fromberg, E. “The Case of the Netherlands: Contradictions and Values in Questioning Prohibition.” 1994 International Report on Drugs, Brussels: International Antiprohibitionist League, 1994. 113-124.
Sandwijk, J.P., et al. Licit and Illicit Drug Use in Amsterdam II. Amsterdam: University of Amsterdam, 1995.
Myth: Marijuana Kills Brain Cells.
Used over time, marijuana permanently alters brain structure and
function, causing memory loss, cognitive impairment, personality
deterioration, and reduced productivity.
Fact: None of the medical tests currently used to
detect brain damage in humans have found harm from marijuana, even from
long term high-dose use. An early study reported brain damage in rhesus
monkeys after six months exposure to high concentrations of marijuana
smoke. In a recent, more carefully conducted study, researchers found
no evidence of brain abnormality in monkeys that were forced to inhale
the equivalent of four to five marijuana cigarettes every day for a
year. The claim that marijuana kills brain cells is based on a
speculative report dating back a quarter of a century that has never
been supported by any scientific study.
Ali, S.F., et al. “Chronic Marijuana Smoke Exposure in the Rhesus
Monkey IV: Neurochemical Effects and Comparison to Acute and Chronic
Exposure to Delta-9-Tetrahydrocannabinol (THC) in Rats.” Pharmacology Biochemistry and Behavior 40 (1991): 677-82.
Myth: Marijuana Impairs Memory and Cognition.
Under the influence of marijuana, people are unable to think rationally
and intelligently. Chronic marijuana use causes permanent mental
Fact: Marijuana produces immediate, temporary
changes in thoughts, perceptions, and information processing. The
cognitive process most clearly affected by marijuana is short-term
memory. In laboratory studies, subjects under the influence of
marijuana have no trouble remembering things they learned previously.
However, they display diminished capacity to learn and recall new
information. This diminishment only lasts for the duration of the
intoxication. There is no convincing evidence that heavy long-term
marijuana use permanently impairs memory or other cognitive functions.
Wetzel, C.D. et al., “Remote Memory During Marijuana Intoxication,” Psychopharmacology 76 (1982): 278-81.
Deadwyler, S.A. et al., “The Effects of Delta-9-THC on Mechanisms of Learning and Memory.” Neurobiology of Drug Abuse: Learning and Memory. Ed. L. Erinoff. Rockville, MD: National Institute on Drug Abuse 1990. 79-83.
Myth: Marijuana Causes Crime.
Marijuana users commit more property offenses than nonusers. Under the
influence of marijuana, people become irrational, aggressive, and
Fact: Every serious scholar and government
commission examining the relationship between marijuana use and crime
has reached the same conclusion: marijuana does not cause crime. The
vast majority of marijuana users do not commit crimes other than the
crime of possessing marijuana. Among marijuana users who do commit
crimes, marijuana plays no causal role. Almost all human and animal
studies show that marijuana decreases rather than increases aggression.
Johnson, L.D., et al. “Drugs and Delinquency: A Search for Causal Connections.” Ed. D.B. Kandel. Longitudinal Research on Drug Use: Empirical Findings and Methodological Issues. New York: John Wiley & Sons, 1978. 137-156.
Goode, E. “Marijuana and Crime.” Marihuana: A Signal of Misunderstanding, Appendix I. National Commission on Marihuana and Drug Abuse Washington, DC: U.S. Government Printing Office, 1972. 447-453.
Abram, K.M. and L.A. Teplin. “Drug Disorder, Mental Illness, and Violence.” Drugs and Violence: Causes, Correlates, and Consequences. Rockville: National Institute on Drug Abuse, 1990. 222-238.
Cherek, D.R., et al. “Acute Effects of Marijuana Smoking on
Aggressive, Escape and Point-Maintained Responding of Male Drug Users.”
Psychopharmacology 111 (1993): 163-168.
Myth: Marijuana Interferes With Male and Female Sex Hormones.
In both men and women, marijuana can cause infertility. Marijuana
retards sexual development in adolescents. It produces feminine
characteristics in males and masculine characteristics in females.
Fact: There is no evidence that marijuana causes
infertility in men or women. In animal studies, high doses of THC
diminish the production of some sex hormones and can impair
reproduction. However, most studies of humans have found that marijuana
has no impact of sex hormones. In those studies showing an impact, it
is modest, temporary, and of no apparent consequence for reproduction.
There is no scientific evidence that marijuana delays adolescent sexual
development, has feminizing effect on males, or a masculinizing effect
Myth: Marijuana Use During Pregnancy Damages the Fetus.
Prenatal marijuana exposure causes birth defects in babies, and, as
they grow older, developmental problems. The health and well being of
the next generation is threatened by marijuana use by pregnant women.
Fact: Studies of newborns, infants, and children
show no consistent physical, developmental, or cognitive deficits
related to prenatal marijuana exposure. Marijuana had no reliable
impact on birth size, length of gestation, neurological development, or
the occurrence of physical abnormalities. The administration of
hundreds of tests to older children has revealed only minor differences
between offspring of marijuana users and nonusers, and some are
positive rather than negative. Two unconfirmed case-control studies
identified prenatal marijuana exposure as one of many factors
statistically associated with childhood cancer. Given other available
evidence, it is highly unlikely that marijuana causes cancer in
Myth: Marijuana Use Impairs the Immune System.
Marijuana users are at increased risk of infection, including HIV. AIDS
patients are particularly vulnerable to marijuana's immunopathic
effects because their immune systems are already suppressed.
Fact: There is no evidence that marijuana users are
more susceptible to infections than nonusers. Nor is there evidence
that marijuana lowers users' resistance to sexually transmitted
diseases. Early studies which showed decreased immune function in cells
taken from marijuana users have since been disproved. Animals given
extremely large doses of THC and exposed to a virus have higher rates
of infection. Such studies have little relevance to humans. Even among
people with existing immune disorders, such as AIDS, marijuana use
appears to be relatively safe. However, the recent finding of an
association between tobacco smoking and lung infection in AIDS patients
warrants further research into possible harm from marijuana smoking in
immune suppressed persons.
Myth: Marijuana's Active Ingredient, THC, Gets Trapped in Body Fat.
Because THC is released from fat cells slowly, psychoactive effects may
last for days or weeks following use. THC's long persistence in the
body damages organs that are high in fat content, the brain in
Fact: Many active drugs enter the body's fat cells.
What is different (but not unique) about THC is that it exits fat cells
slowly. As a result, traces of marijuana can be found in the body for
days or weeks following ingestion. However, within a few hours of
smoking marijuana, the amount of THC in the brain falls below the
concentration required for detectable psychoactivity. The fat cells in
which THC lingers are not harmed by the drug's presence, nor is the
brain or other organs. The most important consequence of marijuana's
slow excretion is that it can be detected in blood, urine, and tissue
long after it is used, and long after its psychoactivity has ended.
DuPont, Robert. Getting Tough on Gateway Drugs. Washington, DC: American Psychiatric Press, 1984. 68.
Myth: Marijuana Use is a Major Cause Of Highway Accidents.
Like alcohol, marijuana impairs psychomotor function and decreases
driving ability. If marijuana use increases, an increase in of traffic
fatalities is inevitable.
Fact: There is no compelling evidence that
marijuana contributes substantially to traffic accidents and
fatalities. At some doses, marijuana affects perception and psychomotor
performances- changes which could impair driving ability. However, in
driving studies, marijuana produces little or no car-handling
impairment- consistently less than produced by low moderate doses of
alcohol and many legal medications. In contrast to alcohol, which tends
to increase risky driving practices, marijuana tends to make subjects
more cautious. Surveys of fatally injured drivers show that when THC is
detected in the blood, alcohol is almost always detected as well. For
some individuals, marijuana may play a role in bad driving. The overall
rate of highway accidents appears not to be significantly affected by
marijuana's widespread use in society.
Myth: Marijuana Related Hospital Emergencies Are Increasing, Particularly Among Youth. This is evidence that marijuana is much more harmful than most people previously believed.
Fact: Marijuana does not cause overdose deaths. The
number of people in hospital emergency rooms who say they have used
marijuana has increased. On this basis, the visit may be recorded as
marijuana-related even if marijuana had nothing to do with the medical
condition preceding the hospital visit. Many more teenagers use
marijuana than use drugs such as heroin and cocaine. As a result, when
teenagers visit hospital emergency rooms, they report marijuana much
more frequently than they report heroin and cocaine. In the large
majority of cases when marijuana is mentioned, other drugs are
mentioned as well. In 1994, fewer than 2% of drug related emergency
room visits involved the use of marijuana.
Shuster, Charles. Quoted in Drug Enforcement Administration. Drug Legalization: Myths and Misconceptions. Washington, DC: U.S. Department of Justice, 1994. 5.
Myth: Marijuana Use Can Be Prevented.
Drug education and prevention programs reduced marijuana use during the
1980s. Since then, our commitment has slackened, and marijuana use has
been rising. By expanding and intensifying current anti-marijuana
messages, we can stop youthful experimentation.
Fact: There is no evidence that anti-drug messages
diminish young people's interest in drugs. Anti-drug campaigns in the
schools and the media may even make drugs more attractive. Marijuana
use among youth declined throughout the 1980s, and began increasing in
the 1990s. This increase occurred despite young people's exposure to
the most massive anti-marijuana campaign in American history. In a
number of other countries, drug education programs are based on a "harm
reduction" model, which seeks to reduce the drug-related harm among
those young people who do experiment with drugs.
Brown, Lee. Director of National Drug Control Policy, remarks at National Conference on Marijuana Use: Prevention, Treatment, and Research. Sponsored by the National Institute on Drug Abuse, Arlington, VA (July 1995).
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