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Marijuana—often called pot, grass, reefer, weed, herb, mary jane, or mj— is
a greenish-gray mixture of the dried, shredded leaves, stems, seeds, and flowers
of Cannabis sativa, the hemp plant. Most users smoke marijuana in handrolled
cigarettes called joints, among other names; some use pipes or water pipes called
bongs. Marijuana cigars called blunts have also become popular. To make blunts,
users slice open cigars and replace the tobacco with marijuana, often combined
with another drug, such as crack cocaine. Marijuana also is used to brew tea
and is sometimes mixed into foods.
The major active chemical in marijuana is delta-9-tetrahydrocannabinol (THC),
which causes the mind-altering effects of marijuana intoxication. The amount
of THC (which is also the psychoactive ingredient in hashish) determines the
potency and, therefore, the effects of marijuana. Between 1980 and 1997, the
amount of THC in marijuana available in the United States rose dramatically.
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Marijuana is the Nation’s most commonly used illicit drug. More than 83 million
Americans (37 percent) age 12 and older have tried marijuana at least once,
according to the 2001 National Household Survey on Drug Abuse (NHSDA).
Marijuana use is widespread among adolescents and young adults. The percentage
of middleschool students who reported using marijuana increased throughout the
early 1990s. In the past few years, according to the 2001 Monitoring the Future
Study, an annual survey of drug use among the Nation’s middleand high-school
students, illicit drug use by 8th-, 10th-, and 12th-graders has leveled off.
Still, in 2001, 20 percent of 8th-graders reported that they had tried marijuana,
and 9 percent were current users (defined as having used the drug in the 30
days preceding the survey). Among 10th-graders, 40 percent had tried marijuana
sometime in their lives, and almost 20 percent were current users. As would
be expected, rates of use among 12th-graders were higher still: Nearly half
had tried marijuana at some time, and 22 percent were current users. The Drug
Abuse Warning Network (DAWN), a system for monitoring the health impact of drugs,
estimated that, in 2001, marijuana was a contributing factor in more than 110,000
emergency department (ED) visits in the United States, with about 15 percent
of the patients between the ages of 12 and 17, and almost two-thirds male.
In 1999, the National Institute of Justice’s Arrestee Drug Abuse Monitoring
Program (ADAM), which collects data from 34 sites on the number of adult arrestees
testing positive for various drugs, found that, on average, 39 percent of adult
male arrestees and 26 percent of adult female arrestees tested positive for
marijuana. ADAM collected data on juvenile arrestees in nine sites and found
that marijuana was the most commonly used drug among these youths. On average,
53 percent of juvenile male and 38 percent of juvenile female arrestees tested
positive for marijuana.
NIDA’s Community Epidemiology Work Group (CEWG), a network of researchers that
tracks trends in the nature and patterns of drug use in major U.S. cities, consistently
reports that marijuana frequently is combined with other drugs, such as crack
cocaine, PCP, formaldehyde, and codeine cough syrup, sometimes without the user
being aware of it. Thus, the risks associated with marijuana use may be compounded
by the risks of added drugs, as well.
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Scientists have learned a great deal about how THC acts in the brain to produce
its many effects. When someone smokes marijuana, THC rapidly passes from the
lungs into the bloodstream, which carries the chemical to organs throughout
the body, including the brain. In the brain, THC connects to specific sites
called cannabinoid receptors on nerve cells and thereby influences the activity
of those cells. Some brain areas have many cannabinoid receptors; others have
few or none. Many cannabinoid receptors are found in the parts of the brain
that influence pleasure, memory, thought, concentration, sensory and time perception,
and coordinated movement.
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Marijuana’s effects begin immediately after the drug enters the brain and last
from 1 to 3 hours. If marijuana is consumed in food or drink, the short-term
effects begin more slowly, usually in 1/2 to 1 hour, and last longer, for as
long as 4 hours. Smoking marijuana deposits several times more THC into the
blood than does eating or drinking the drug.
Within a few minutes after inhaling marijuana smoke, an individual’s heart
begins beating more rapidly, the bronchial passages relax and become enlarged,
and blood vessels in the eyes expand, making the eyes look red. The heart rate,
normally 70 to 80 beats per minute, may increase by 20 to 50 beats per minute
or, in some cases, even double. This effect can be greater if other drugs are
taken with marijuana.
As THC enters the brain, it causes a user to feel euphoric— or “high”—by acting
in the brain’s reward system, areas of the brain that respond to stimuli such
as food and drink as well as most drugs of abuse. THC activates the reward system
in the same way that nearly all drugs of abuse do, by stimulating brain cells
to release the chemical dopamine.
A marijuana user may experience pleasant sensations, colors and sounds may
seem more intense, and time appears to pass very slowly. The user’s mouth feels
dry, and he or she may suddenly become very hungry and thirsty. His or her hands
may tremble and grow cold. The euphoria passes after awhile, and then the user
may feel sleepy or depressed. Occasionally, marijuana use produces anxiety,
fear, distrust, or panic.
Marijuana use impairs a person’s ability to form memories, recall events (see
Marijuana, Memory, and the Hippocampus), and shift attention from one thing
to another. THC also disrupts coordination and balance by binding to receptors
in the cerebellum and basal ganglia, parts of the brain that regulate balance,
posture, coordination of movement, and reaction time. Through its effects on
the brain and body, marijuana intoxication can cause accidents. Studies show
that approximately 6 to 11 percent of fatal accident victims test positive for
THC. In many of these cases, alcohol is detected as well.
In a study conducted by the National Highway Traffic Safety Administration,
a moderate dose of marijuana alone was shown to impair driving performance;
however, the effects of even a low dose of marijuana combined with alcohol were
markedly greater than for either drug alone. Driving indices measured included
reaction time, visual search frequency (driver checking side streets), and the
ability to perceive and/or respond to changes in the relative velocity of other
Marijuana users who have taken high doses of the drug may experience acute
toxic psychosis, which includes hallucinations, delusions, and depersonalization—
a loss of the sense of personal identity, or self-recognition. Although the
specific causes of these symptoms remain unknown, they appear to occur more
frequently when a high dose of cannabis is consumed in food or drink rather
|Marijuana, Memory, and the Hippocampus
Marijuana’s damage to short-term memory seems to occur because THC alters
the way in which information is processed by the hippocampus, a brain
area responsible for memory formation. Laboratory rats treated with THC
displayed the same reduced ability to perform tasks requiring short-term
memory as other rats showed after nerve cells in their hippocampus were
destroyed. In addition, the THC-treated rats had the greatest difficulty
with the tasks precisely during the time when the drug was interfering
most with the normal functioning of cells in the hippocampus.
As people age, they normally lose neurons in the hippocampus, which decreases
their ability to remember events. Chronic THC exposure may hasten the
age-related loss of hippocampal neurons. In one series of studies, rats
exposed to THC every day for 8 months (approximately 30 percent of their
lifespan), when examined at 11 to 12 months of age, showed nerve cell
loss equivalent to that of unexposed animals twice their age.
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Marijuana use has been shown to increase users’ difficulty in trying to quit
smoking tobacco. This was recently reported in a study comparing smoking cessation
in adults who smoked both marijuana and tobacco with those who smoked only tobacco.
The relationship between marijuana use and continued smoking was particularly
strong in those who smoked marijuana daily at the time of the initial interview,
13 years prior to the followup interview.
A study of 450 individuals found that people who smoke marijuana frequently
but do not smoke tobacco have more health problems and miss more days of work
than nonsmokers do. Many of the extra sick days used by the marijuana smokers
in the study were for respiratory illnesses.
Even infrequent marijuana use can cause burning and stinging of the mouth and
throat, often accompanied by a heavy cough. Someone who smokes marijuana regularly
may have many of the same respiratory problems that tobacco smokers do, such
as daily cough and phlegm production, more frequent acute chest illnesses, a
heightened risk of lung infections, and a greater tendency toward obstructed
Cancer of the respiratory tract and lungs may also be promoted by marijuana
smoke. A study comparing 173 cancer patients and 176 healthy individuals produced
strong evidence that smoking marijuana increases the likelihood of developing
cancer of the head or neck, and that the more marijuana smoked, the greater
the increase. A statistical analysis of the data suggested that marijuana smoking
doubled or tripled the risk of these cancers.
Marijuana has the potential to promote cancer of the lungs and other parts
of the respiratory tract because it contains irritants and carcinogens. In fact,
marijuana smoke contains 50 percent to 70 percent more carcinogenic hydrocarbons
than does tobacco smoke. It also produces high levels of an enzyme that converts
certain hydrocarbons into their carcinogenic form, levels that may accelerate
the changes that ultimately produce malignant cells. Marijuana users usually
inhale more deeply and hold their breath longer than tobacco smokers do, which
increases the lungs’ exposure to carcinogenic smoke. These facts suggest that,
puff for puff, smoking marijuana may increase the risk of cancer more than smoking
Some adverse health effects caused by marijuana may occur because THC impairs
the immune system’s ability to fight off infectious diseases and cancer. In
laboratory experiments that exposed animal and human cells to THC or other marijuana
ingredients, the normal disease-preventing reactions of many of the key types
of immune cells were inhibited. In other studies, mice exposed to THC or related
substances were more likely than unexposed mice to develop bacterial infections
One study has indicated that a person’s risk of heart attack during the first
hour after smoking marijuana is four times his or her usual risk. The researchers
suggest that a heart attack might occur, in part, because marijuana raises blood
pressure and heart rate and reduces the oxygencarrying capacity of blood.
|Health Consequences of Marijuana Abuse
Acute (present during intoxication)
- Impairs short-term memory
- Impairs attention, judgment, and other cognitive functions
- Impairs coordination and balance
- Increases heart rate
Persistent (lasting longer than intoxication, but may not be permanent)
- Impairs memory and learning skills
Long-term (cumulative, potentially permanent effects of chronic abuse)
- Can lead to addiction
- Increases risk of chronic cough, bronchitis, and emphysema
- Increases risk of cancer of the head, neck, and lungs
|The Science of Medical Marijuana
THC,the main active ingredient in marijuana, produces effects that
potentially can be useful for treating a variety of medical conditions.
It is the main ingredient in an oral medication that is currently used
to treat nausea in cancer chemotherapy patients and to stimulate appetite
in patients with wasting due to AIDS. Scientists are continuing to investigate
other potential medical uses for cannabinoids. Research is underway to
examine the effects of smoked marijuana and extracts of marijuana on appetite
stimulation, certain types of pain, and spasticity due to multiple sclerosis.
However, the inconsistency of THC dosage in different marijuana samples
poses a major hindrance to valid trials and to the safe and effective
use of the drug. Moreover, the adverse effects of marijuana smoke on the
respiratory system will offset the helpfulness of smoked marijuana for
some patients. Finally, little is known about the many chemicals besides
THC that are in marijuana, or their possible deleterious impact on patients
with medical conditions.
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Students who smoke marijuana get lower grades and are less likely to graduate
from high school, compared with their nonsmoking peers. Workers who smoke marijuana
are more likely than their coworkers to have problems on the job. Several studies
have associated workers’ marijuana smoking with increased absences, tardiness,
accidents, workers’ compensation claims, and job turnover. A study among municipal
workers found that employees who smoked marijuana on or off the job reported
more “withdrawal behaviors” —such as leaving work without permission, daydreaming,
spending work time on personal matters, and shirking tasks—that adversely affect
productivity and morale.
Depression, anxiety, and personality disturbances are all associated with marijuana
use. Research clearly demonstrates that marijuana use has the potential to cause
problems in daily life or make a person’s existing problems worse. Because marijuana
compromises the ability to learn and remember information, the more a person
uses marijuana the more he or she is likely to fall behind in accumulating intellectual,
job, or social skills. In one study of cognition, adults were matched on the
basis of their performance in the 4th grade on the Iowa test of Basic Skills.
They were evaluated on a number of cognitive measures including the 12th grade
version of the Iowa Test. Those who were heavy marijuana smokers scored significantly
lower on mathematical skills and verbal expression than non-smokers.
Moreover, research has shown that marijuana’s adverse impact on memory and
learning can last for days or weeks after the acute effects of the drug wear
off. For example, a study of 129 college students found that among heavy users
of marijuana, those who smoked the drug at least 27 of the preceding 30 days,
critical skills related to attention, memory, and learning were significantly
impaired, even after they had not used the drug for at least 24 hours. The heavy
marijuana users in the study had more trouble sustaining and shifting their
attention and in registering, organizing, and using information than did the
study participants who had used marijuana no more than 3 of the previous 30
days. As a result, someone who smokes marijuana once daily may be functioning
at a reduced intellectual level all of the time. More recently, the same researchers
showed that a group of long-term heavy marijuana users’ ability to recall words
from a list was impaired 1 week following cessation of marijuana use, but returned
to normal by 4 weeks. An implication of this finding is that even after long-term
heavy marijuana use, if an individual quits marijuana use, some cognitive abilities
may be recovered.
Another study produced additional evidence that marijuana’s effects on the
brain can cause cumulative deterioration of critical life skills in the long
run. Researchers gave students a battery of tests measuring problemsolving and
emotional skills in 8th grade and again in 12th grade. The results showed that
the students who were already drinking alcohol plus smoking marijuana in 8th grade started off slightly behind
their peers but that the distance
separating these two groups
grew significantly by their senior
year in high school. The analysis linked marijuana use, independently
of alcohol use, to reduced
capacity for self-reinforcement, a
group of psychological skills that
enable individuals to maintain
confidence and persevere in the
pursuit of goals.
|The Body’s Natural THC-Like Chemicals
THCowes many of its effects to its similarity to a family of chemicals
called the endogenous cannabinoids, which are natural Cannabislike chemicals.
Because a THC molecule is shaped like these endogenous cannabinoids, it
interacts with the same receptors on nerve cells, the cannabinoid receptors,
that endogenous cannabinoids do, and it influences many of the same processes.
Research has shown that the endogenous cannabinoids help control a wide
array of mental and physical processes in the brain and throughout the
body, including memory and perception, fine motor coordination, pain sensations,
immunity to disease, and reproduction.
When someone smokes marijuana, THC overstimulates the cannabinoid receptors,
leading to a disruption of the endogenous cannabinoids’ normal control.
This overstimulation produces the intoxication experienced by marijuana
smokers. Over time, it may degrade some cannabinoid receptors, possibly
producing permanent adverse effects and contributing to addiction and
risk for a withdrawal syndrome.
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Research has shown that babies born to women who used marijuana during their
pregnancies display altered responses to visual stimuli, increased tremulousness,
and a high-pitched cry, which may indicate problems with neurological development.
During infancy and preschool years, marijuanaexposed children have been observed
to have more behavioral problems and to perform tasks of visual perception,
language comprehension, sustained attention, and memory more poorly than nonexposed
children do. In school, these children are more likely to exhibit deficits in
decision-making skills, memory, and the ability to remain attentive.
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Long-term marijuana use can lead to addiction for some people; that is, they
use the drug compulsively even though it often interferes with family, school,
work, and recreational activities. According to the 2001 National Household
Survey on Drug Abuse, an estimated 5.6 million Americans age 12 or older reported
problems with illicit drug use in the past year. Of these, 3.6 million met diagnostic
criteria for dependence on an illicit drug. More than 2 million met diagnostic
criteria for dependence on marijuana/hashish. In 1999, more than 220,000 people
entering drug abuse treatment programs reported that marijuana was their primary
drug of abuse.
Along with craving, withdrawal symptoms can make it hard for long-term marijuana
smokers to stop using the drug. People trying to quit report irritability, difficulty
sleeping, and anxiety. They also display increased aggression on psychological
tests, peaking approximately 1 week after they last used the drug.
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Treatment programs directed at marijuana abuse are rare, partly because many
who use marijuana do so in combination with other drugs, such as cocaine and
alcohol. However, with more people seeking help to control marijuana abuse,
research has focused on ways to overcome problems with abuse of this drug.
One study of adult marijuana users found comparable benefits from a 14-session
cognitivebehavioral group treatment and a 2-session individual treatment that
included motivational interviewing and advice on ways to reduce marijuana use.
Participants were mostly men in their early thirties who had smoked marijuana
daily for over 10 years. By increasing patients’ awareness of what triggers
their marijuana use, both treatments sought to help them devise avoidance strategies.
Use, dependence symptoms, and psychosocial problems decreased for at least 1
year after both treatments. About 30 percent of users were abstinent during
the last 3-month followup period. Another study suggests that giving patients
vouchers for abstaining from marijuana can improve outcomes. Vouchers can be
redeemed for such goods as movie passes, sports equipment, or vocational training.
No medications are now available to treat marijuana abuse. However, recent
discoveries about the workings of THC receptors have raised the possibility
that scientists may eventually develop a medication that will block THC’s intoxicating
effects. Such a medication might be used to prevent relapse to marijuana abuse
by reducing or eliminating its appeal.
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