April 2006 Page 1 of 8

Marijuana is the most commonly abused

illicit drug in the United States. A dry,

shredded green/brown mix of flowers,

stems, seeds, and leaves of the hemp

plant Cannabis sativa, it usually is

smoked as a cigarette (joint, nail), or in

a pipe (bong). It also is smoked in

blunts, which are cigars that have been

emptied of tobacco and refilled with

marijuana, often in combination with

another drug. It might also be mixed in

food or brewed as a tea. As a more

concentrated, resinous form it is called

hashish and, as a sticky black liquid,

hash oil. Marijuana smoke has a pungent and distinctive, usually sweet-andsour odor. There are countless street

terms for marijuana including pot, herb,

weed, grass, widow, ganja, and hash,

as well as terms derived from trademarked varieties of cannabis, such as

Bubble Gum, Northern Lights, Fruity

Juice, Afghani #1, and a number of

Skunk varieties. 

The main active chemical in marijuana is

THC (delta-9-tetrahydrocannabinol). The

membranes of certain nerve cells in the

brain contain protein receptors that bind

to THC. Once securely in place, THC

kicks off a series of cellular reactions

that ultimately lead to the high that users

experience when they smoke marijuana. 

Extent of Use ———

In 2004, 14.6 million Americans age

12 and older used marijuana at least

once in the month prior to being surveyed. About 6,000 people a day in

2004 used marijuana for the first time—

2.1 million Americans. Of these, 63.8

percent were under age 18(1). In the last

half of 2003, marijuana was the third

most commonly abused drug mentioned

in drug-related hospital emergency

department (ED) visits in the continental

United States, at 12.6 percent, following

cocaine (20 percent) and alcohol (48.7

percent)(2).

Marijuana

1996 1997 1998 1999 2000 2001 2002 2003 2004 2005

Lifetime 23.1% 22.6% 22.2% 22.0% 20.3% 20.4% 19.2% 17.5% 16.3% 16.5%

Annual 18.3 17.7 16.9 16.5 15.6 15.4 14.6 12.8 11.8 12.2

30-day 11.3 10.2 9.7 9.7 9.1 9.2 8.3 7.5 6.4 6.6

Daily 1.5 1.1 1.1 1.4 1.3 1.3 1.2 1.0 0.8 1.0

Percentage of 8th-Graders Who Have Used Marijuana

Monitoring the Future Survey, 2005
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Prevalence of lifetime,* annual, and use

within the last 30 days for marijuana

remained stable among 10th- and 12thgraders surveyed between 2003 and

2004. However, 8th-graders reported a

significant decline in 30-day use and a

significant increase in perceived harmfulness of smoking marijuana once or twice

and regularly(3). Trends in disapproval of

using marijuana once or twice and

occasionally rose among 8th-graders as

well, and 10th-graders reported an

increase in disapproval of occasional

and regular use for the same period(3).

Effects on the Brain

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 influences the activity of

those cells. Some brain areas have

many cannabinoid receptors; others

Percentage of 10th-Graders Who Have Used Marijuana

Monitoring the Future Survey, 2005

1996 1997 1998 1999 2000 2001 2002 2003 2004 2005

Lifetime 39.8% 42.3% 39.6% 40.9% 40.3% 40.1% 38.7% 36.4% 35.1% 34.1%

Annual 33.6 34.8 31.1 32.1 32.2 32.7 30.3 28.2 27.5 26.6

30-day 20.4 20.5 18.7 19.4 19.7 19.8 17.8 17.0 15.9 15.2

Daily 3.5 3.7 3.6 3.8 3.8 4.5 3.9 3.6 3.2 3.1

Percentage of 12th-Graders Who Have Used Marijuana

Monitoring the Future Survey, 2005

1996 1997 1998 1999 2000 2001 2002 2003 2004 2005

Lifetime 44.9% 49.6% 49.1% 49.7% 48.8% 49.0% 47.8% 46.1% 45.7% 44.8%

Annual 35.8 38.5 37.5 37.8 36.5 37.0 36.2 34.9 34.3 33.6

30-day 21.9 23.7 22.8 23.1 21.6 22.4 21.5 21.2 19.9 19.8

Daily 4.9 5.8 5.6 6.0 6.0 5.8 6.0 6.0 5.6 5.0

*“Lifetime” refers to use at least once during a respondent’s lifetime. “Annual” refers to use at least once during the

year preceding an individual’s response to the survey. “30-day” refers to use at least once during the 30 days preceding an individual’s response to the survey.
April 2006 Page 3 of 8

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(4).

The short-term effects of marijuana can

include problems with memory and

learning; distorted perception; difficulty

in thinking and problem solving; loss of

coordination; and increased heart rate.

Research findings for long-term marijuana abuse indicate some changes in the

brain similar to those seen after longterm abuse of other major drugs. For

example, cannabinoid (THC or synthetic

forms of THC) withdrawal in chronically

exposed animals leads to an increase in

the activation of the stress-response system(5) and changes in the activity of

nerve cells containing dopamine(6).

Dopamine neurons are involved in the

regulation of motivation and reward,

and are directly or indirectly affected by

all drugs of abuse.

Effects on the Heart

One study has indicated that an

abuser’s risk of heart attack more than

quadruples in the first hour after smoking

marijuana(7). The researchers suggest that

such an effect might occur from marijuana’s effects on blood pressure and heart

rate and reduced oxygen-carrying

capacity of blood.

Effects on the Lungs

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(8). Many of the

extra sick days among the marijuana

smokers in the study were for respiratory

illnesses.

Even infrequent abuse 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 illness, a heightened risk of lung infections, and a greater tendency to

obstructed airways(9). Smoking marijuana possibly increases the likelihood of

developing cancer of the head or neck.

A study comparing 173 cancer patients

and 176 healthy individuals produced

evidence that marijuana smoking doubled or tripled the risk of these

cancers(10).

Marijuana abuse also has the potential

to promote cancer of the lungs and other

parts of the respiratory tract because it

contains irritants and carcinogens(9, 11). In

fact, marijuana smoke contains 50 to 70

percent more carcinogenic hydrocarbons than does tobacco smoke(12). It also

induces high levels of an enzyme that
April 2006 Page 4 of 8

converts certain hydrocarbons into their

carcinogenic form—levels that may

accelerate the changes that ultimately

produce malignant cells(13). 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 be more harmful to the

lungs than smoking tobacco.

Other Health Effects

Some of marijuana’s adverse health

effects may occur because THC impairs

the immune system’s ability to fight disease. 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(14). In other studies, mice

exposed to THC or related substances

were more likely than unexposed mice

to develop bacterial infections and

tumors(15, 16).

Effects of Heavy Marijuana Use

on Learning and Social Behavior

Research clearly demonstrates that marijuana has the potential to cause problems in daily life or make a person’s

existing problems worse. Depression(17),

anxiety(17), and personality disturbances(18) have been associated with

chronic marijuana use. 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. 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(19, 20, 25).

Students who smoke marijuana get

lower grades and are less likely to graduate from high school, compared with

their nonsmoking peers(21, 22, 23, 24). A study

of 129 college students found that,

among those who smoked the drug at

least 27 of the 30 days prior to being

surveyed, critical skills related to attention, memory, and learning were significantly impaired, even after the students

had not taken the drug for at least 24

hours(20). These “heavy” marijuana

abusers had more trouble sustaining and

shifting their attention and in registering,

organizing, and using information than

did the study participants who had

abused marijuana no more than 3 of the

previous 30 days. As a result, someone

who smokes marijuana every day may

be functioning at a reduced intellectual

level all of the time.

More recently, the same researchers

showed that the ability of a group of

long-term heavy marijuana abusers to

recall words from a list remained

impaired for a week after quitting, but

returned to normal within 4 weeks(25).

Thus, some cognitive abilities may be

restored in individuals who quit smoking

marijuana, even after long-term heavy use.
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Workers who smoke marijuana are more

likely than their coworkers to have problems on the job. Several studies associate workers’ marijuana smoking with

increased absences, tardiness, accidents, workers’ compensation claims,

and job turnover. A study among postal

workers found that employees who tested positive for marijuana on a preemployment urine drug test had 55 percent more industrial accidents, 85 percent more injuries, and a 75-percent

increase in absenteeism compared with

those who tested negative for marijuana

use(26). In another study, heavy marijuana

abusers reported that the drug impaired

several important measures of life

achievement including cognitive abilities,

career status, social life, and physical

and mental health(27).

Effects of Exposure During

Pregnancy

Research has shown that some babies

born to women who abused marijuana

during their pregnancies display altered

responses to visual stimuli(28), increased

tremulousness, and a high-pitched cry,

which may indicate neurological problems in development(29). During the preschool years, marijuana-exposed children have been observed to perform

tasks involving sustained attention and

memory more poorly than nonexposed

children do(30, 31). In the school years,

these children are more likely to exhibit

deficits in problem-solving skills, memory, and the ability to remain attentive(30).

Addictive Potential

Long-term marijuana abuse can lead to

addiction for some people; that is, they

abuse the drug compulsively even

though it interferes with family, school,

work, and recreational activities. Drug

craving and withdrawal symptoms can

make it hard for long-term marijuana

smokers to stop abusing the drug.

People trying to quit report irritability,

sleeplessness, and anxiety(32). They also

display increased aggression on psychological tests, peaking approximately one

week after the last use of the drug(33).

Genetic Vulnerability

Scientists have found that whether an

individual has positive or negative sensations after smoking marijuana can be

influenced by heredity. A 1997 study

demonstrated that identical male twins

were more likely than nonidentical male

twins to report similar responses to marijuana abuse, indicating a genetic basis

for their response to the drug(34).

(Identical twins share all of their genes.)

It also was discovered that the twins’

shared or family environment before age

18 had no detectable influence on their

response to marijuana. Certain environmental factors, however, such as the

availability of marijuana, expectations

about how the drug would affect them,

the influence of friends and social contacts, and other factors that differentiate

experiences of identical twins were

found to have an important effect.(34)
April 2006 Page 6 of 8

Treating Marijuana Problems

The latest treatment data indicate that, in

2002, marijuana was the primary drug

of abuse in about 15 percent (289,532)

of all admissions to treatment facilities in

the United States. Marijuana admissions

were primarily male (75 percent), White

(55 percent), and young (40 percent

were in the 15–19 age range). Those in

treatment for primary marijuana abuse

had begun use at an early age; 56 percent had abused it by age 14 and 92

percent had abused it by 18(35).

One study of adult marijuana abusers

found comparable benefits from a 14-

session cognitive-behavioral 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 more than

10 years. By increasing patients’ awareness of what triggers their marijuana

abuse, both treatments sought to help

patients devise avoidance strategies.

Abuse, dependence symptoms, and psychosocial problems decreased for at

least 1 year following both treatments;

about 30 percent of the patients were

abstinent during the last 3-month followup period(36).

Another study suggests that giving

patients vouchers that they can redeem

for goods—such as movie passes, sporting equipment, or vocational training—

may further improve outcomes(37).

Although no medications are currently

available for treating marijuana abuse,

recent discoveries about the workings of

the THC receptors have raised the possibility of eventually developing a medication that will block the intoxicating

effects of THC. Such a medication might

be used to prevent relapse to marijuana

abuse by lessening or eliminating its

appeal.

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