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Marijuana is the most commonly abused

illicit drug in the United States. It is a

dry, shredded green and brown mix 

of flowers, stems, seeds, and leaves

derived from the hemp plant Cannabis

sativa. The main active chemical in marijuana is delta-9-tetrahydrocannabinol;

THC for short. 

How is Marijuana Abused?

Marijuana is usually smoked as a 

cigarette (joint) or in a pipe. It is also

smoked in blunts, which are cigars that

have been emptied of tobacco and

refilled with marijuana. Since the blunt

retains the tobacco leaf used to wrap

the cigar, this mode of delivery combines marijuana's active ingredients with

nicotine and other harmful chemicals.

Marijuana can 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-and-sour odor. 

How Does Marijuana Affect

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 the brain

and other organs throughout the body.

THC acts upon specific sites in the brain,

called cannabinoid receptors, kicking off

a series of cellular reactions that ultimately lead to the “high” that users experience when they smoke marijuana. Some

brain areas have many cannabinoid

receptors; others have few or none. The

highest density of cannabinoid receptors

are found in parts of the brain that influence pleasure, memory, thoughts, concentration, sensory and time perception,

and coordinated movement.1

Not surprisingly, marijuana intoxication

can cause distorted perceptions, impaired

coordination, difficulty in thinking and

problem solving, and problems with

learning and memory. Research has

shown that marijuana’s adverse impact

on learning and memory can last for

days or weeks after the acute effects of

the drug wear off.2 As a result, someone

who smokes marijuana every day may be

functioning at a suboptimal intellectual

level all of the time.

Research on the long-term effects of marijuana abuse indicates some changes in

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

example, cannabinoid withdrawal in

Marijuana
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chronically exposed animals leads to an

increase in the activation of the stressresponse system3 and changes in the

activity of nerve cells containing

dopamine.4 Dopamine neurons are

involved in the regulation of motivation

and reward, and are directly or indirectly

affected by all drugs of abuse.

Addictive Potential

Long-term marijuana abuse can lead to

addiction; that is, compulsive drug seeking and abuse despite its known harmful

effects upon social functioning in the context of family, school, work, and recreational activities. Long-term marijuana

abusers trying to quit report irritability,

sleeplessness, decreased appetite, anxiety, and drug craving, all of which make

it difficult to quit. These withdrawal symptoms begin within about 1 day following

abstinence, peak at 2–3 days, and subside within 1 or 2 weeks following drug

cessation.5

Marijuana and Mental Health

A number of studies have shown an

association between chronic marijuana

use and increased rates of anxiety,

depression, suicidal ideation, and schizophrenia. Some of these studies have

shown age at first use to be a factor,

where early use is a marker of vulnerability to later problems. However, at this

time, it not clear whether marijuana use

causes mental problems, exacerbates

them, or is used in attempt to self-medicate symptoms already in existence.

Chronic marijuana use, especially in a

very young person, may also be a marker of risk for mental illnesses, including

addiction, stemming from genetic or

environmental vulnerabilities, such as

early exposure to stress or violence. At

the present time, the strongest evidence

links marijuana use and schizophrenia

and/or related disorders.6 High doses of

marijuana can produce an acute psychotic reaction, and research suggests

that in vulnerable individuals, marijuana

use may be a factor that increases risk

for the disease. 

What Other Adverse Effect

Does Marijuana Have on

Health?

Effects on the Heart

One study found 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 outcome might occur from marijuana’s

effects on blood pressure and heart rate

(it increases both) and reduced oxygencarrying capacity of blood.

Effects on the Lungs

Numerous studies have shown marijuana smoke to contain carcinogens and to

be an irritant to the lungs. In fact, marijuana smoke contains 50 to 70 percent

more carcinogenic hydrocarbons than

tobacco smoke. Marijuana users usually

inhale more deeply and hold their

breath longer than tobacco smokers do,
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which further increases the lungs’ exposure to carcinogenic smoke. Marijuana

smokers show dysregulated growth of

epithelial cells in their lung tissue, which

could lead to cancer;8 however, a recent

case-controlled study found no positive

associations between marijuana use and

lung, upper respiratory, or upper digestive tract cancers.9 Thus, the link between

marijuana smoking and these cancers

remains unsubstantiated at this time.

Nonetheless, marijuana smokers can

have many of the same respiratory problems as tobacco smokers, such as daily

cough and phlegm production, more frequent acute chest illness, a heightened

risk of lung infections, and a greater tendency toward obstructed airways. 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.10 Many of the extra

sick days among the marijuana smokers

in the study were for respiratory illnesses.

Effects on Daily Life 

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

existing problems worse. In one study,

heavy marijuana abusers reported that

the drug impaired several important

measures of life achievement including

physical and mental health, cognitive

abilities, social life, and career status.11

Several studies associate workers’ marijuana smoking with increased absences,

tardiness, accidents, workers’ compensation claims, and job turnover. 

What Treatment Options

Exist?

Behavioral interventions, including cognitive behavioral therapy and motivational incentives (i.e., providing vouchers 

for goods or services to patients who

remain abstinent) have shown efficacy 

in treating marijuana dependence.

Although no medications are currently

available, recent discoveries about the

workings of the cannabinoid system

offer promise for the development of

medications to ease withdrawal, block

the intoxicating effects of marijuana, 

and prevent relapse. 

The latest treatment data indicate that in

2006 marijuana was the most common

illicit drug of abuse and was responsible

for about 16 percent (289,988) of all

admissions to treatment facilities in the

United States. Marijuana admissions

were primarily male (73.8 percent),

White (51.5 percent), and young (36.1

percent were in the 15–19 age range).

Those in treatment for primary marijuana

abuse had begun use at an early age:

56.2 percent had abused it by age 14

and 92.5 percent had abused it by age

18.††
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How Widespread is

Marijuana Abuse?

According to the National Survey on

Drug Use and Health, in 2006, 14.8

million Americans age 12 or older used

marijuana at least once in the month

prior to being surveyed, which is similar

to the 2005 rate. About 6,000 people a

day in 2006 used marijuana for the first

time—2.2 million Americans. Of these,

63.3 percent were under age 18.†††

Monitoring the Future Survey

According to the 2007 Monitoring the

Future survey—a national survey of 8th,

10th, and 12th graders, marijuana use

has been declining since the late 1990s.

Between 2000 and 2007, past-year use

decreased more than 20 percent in all

three grades combined. Nevertheless,

marijuana use remains at unacceptably

high levels, with more than 40 percent

of high school seniors reporting use at

least once in their lifetimes.†††† 

Percentage of 10th Graders Who Have Used Marijuana

Percentage of 12th Graders Who Have Used Marijuana

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

year preceding an individual’s response to the survey. “Past month” refers to use at least once during the 30 days 

preceding an individual’s response to the survey. 

1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007

Lifetime 22.6 22.2 22.0 20.3 20.4 19.2 17.5 16.3 16.5 15.7 14.2

Past year 17.7 16.9 16.5 15.6 15.4 14.6 12.8 11.8 12.2 11.7 10.3

Past month 10.2 9.7 9.7 9.1 9.2 8.3 7.5 6.4 6.6 6.5 5.7

Daily 1.1 1.1 1.4 1.3 1.3 1.2 1.0 0.8 1.0 1.0 0.8

Percentage of 8th Graders Who Have Used Marijuana

1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007

Lifetime 42.3 39.6 40.9 40.3 40.1 38.7 36.4 35.1 34.1 31.8 31.0

Past year 34.8 31.1 32.1 32.2 32.7 30.3 28.2 27.5 26.6 25.2 24.6

Past month 20.5 18.7 19.4 19.7 19.8 17.8 17.0 15.9 15.2 14.2 14.2

Daily 3.7 3.6 3.8 3.8 4.5 3.9 3.6 3.2 3.1 2.8 2.8

1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007

Lifetime 49.6 49.1 49.7 48.8 49.0 47.8 46.1 45.7 44.8 42.3 41.8

Past year 38.5 37.5 37.8 36.5 37.0 36.2 34.9 34.3 33.6 31.5 31.7

Past month 23.7 22.8 23.1 21.6 22.4 21.5 21.2 19.9 19.8 18.3 18.8

Daily 5.8 5.6 6.0 6.0 5.8 6.0 6.0 5.6 5.0 5.0 5.1
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Data Sources

† For street terms searchable by drug name, street term, cost and quantities, drug trade, and drug use, visit:

http://www.whitehousedrugpolicy.gov/streetterms/default.asp.

†† These data are from the Treatment Episode Data Set (TEDS) Highlights – 2006: National Admissions to Substance

Abuse Treatment Services (Office of Applied Studies, DASIS Series: S-40, DHHS Publication No. SMA 08-4313,

Rockville, MD, 2008), funded by the Substance Abuse and Mental Health Services Administration. The latest data are

available at 800-729-6686 or online at www.samhsa.gov.

††† Results from the 2006 National Survey on Drug Use and Health: National Findings (Office of Applied Studies,

NSDUH Series H–32, DHHS Publication No. SMA 07-4293 Rockville, MD, 2007). NSDUH is an annual survey conducted by the Substance Abuse and Mental Health Services Administration. Copies of the latest survey are available

from the National Clearinghouse for Alcohol and Drug Information at 800-729-6686.

†††† These data are from the 2007 Monitoring the Future survey, funded by the National Institute on Drug Abuse,

National Institutes of Health, DHHS, and conducted annually by the University of Michigan’s Institute for Social

Research. The survey has tracked 12th graders’ illicit drug use and related attitudes since 1975; in 1991, 8th and

10th graders were added to the study. The latest data are online at www.drugabuse.gov. 

References

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87(5):1932–1936, 1990.

2 Pope HG, Gruber AJ, Hudson JI, Huestis MA, Yurgelun-Todd D. Neuropsychological performance in long-term

cannabis users. Arch Gen Psychiatry 58(10):909–915, 2001. 

3 Rodríguez de Fonseca F, Carrera MRA, Navarro M, Koob GF, Weiss F. Activation of corticotropin-releasing factor in

the limbic system during cannabinoid withdrawal. Science 276(5321):2050–2054, 1997.

4 Diana M, Melis M, Muntoni AL, Gessa GL. Mesolimbic dopaminergic decline after cannabinoid withdrawal. Proc

Natl Acad Sci, USA 95(17):10269–10273, 1998.

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National Institutes of Health – U.S. Department of Health and Human Services

This material may be used or reproduced without permission from NIDA. Citation of the source is appreciated.