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-and-sour 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 181.
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.
Prevalence of lifetime,* annual, and use within the
last 30 days for marijuana remained stable among
10th- and 12th-graders 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 regularly3.
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 period3.
Percentage of
8th-Graders Who Have Used Marijuana:
Monitoring the Future Study, 2005
|
|
1994 |
1995 |
1996 |
1997 |
1998 |
1999 |
|
Lifetime |
16.7% |
19.9% |
23.1% |
22.6% |
22.2% |
22.0% |
|
Annual |
13.0 |
15.8 |
18.3 |
17.7 |
16.9 |
16.5 |
|
30-day |
7.8 |
9.1 |
11.3 |
10.2 |
9.7 |
9.7 |
|
Daily |
0.7 |
0.8 |
1.5 |
1.1 |
1.1 |
1.4 |
|
|
|
2000 |
2001 |
2002 |
2003 |
2004 |
2005 |
|
Lifetime |
20.3% |
20.4% |
19.2% |
17.5% |
16.3% |
16.5% |
|
Annual |
15.6 |
15.4 |
14.6 |
12.8 |
11.8 |
12.2 |
|
30-day |
9.1 |
9.2 |
8.3 |
7.5 |
6.4 |
6.6 |
|
Daily |
1.3 |
1.3 |
1.2 |
1.0 |
0.8 |
1.0 |
|
Percentage of
10th-Graders Who Have Used Marijuana:
Monitoring the Future Study, 2005
|
|
1994 |
1995 |
1996 |
1997 |
1998 |
1999 |
|
Lifetime |
30.4% |
34.1% |
39.8% |
42.3% |
39.6% |
40.9% |
|
Annual |
25.2 |
28.7 |
33.6 |
34.8 |
31.1 |
32.1 |
|
30-day |
15.8 |
17.2 |
20.4 |
20.5 |
18.7 |
19.4 |
|
Daily |
2.2 |
2.8 |
3.5 |
3.7 |
3.6 |
3.8 |
|
|
|
2000 |
2001 |
2002 |
2003 |
2004 |
2005 |
|
Lifetime |
40.3% |
40.1% |
38.7% |
36.4% |
35.1% |
34.1% |
|
Annual |
32.2 |
32.7 |
30.3 |
28.2 |
27.5 |
26.6 |
|
30-day |
19.7 |
19.8 |
17.8 |
17.0 |
15.9 |
15.2 |
|
Daily |
3.8 |
4.5 |
3.9 |
3.6 |
3.2 |
3.1 |
|
Percentage of
12th-Graders Who Have Used Marijuana
Monitoring the Future Study, 2005
|
|
1994 |
1995 |
1996 |
1997 |
1998 |
1999 |
|
Lifetime |
38.2% |
41.7% |
44.9% |
49.6% |
49.1% |
49.7% |
|
Annual |
30.7 |
34.7 |
35.8 |
38.5 |
37.5 |
37.8 |
|
30-day |
19.0 |
21.2 |
21.9 |
23.7 |
22.8 |
23.1 |
|
Daily |
3.6 |
4.6 |
4.9 |
5.8 |
5.6 |
6.0 |
|
|
|
2000 |
2001 |
2002 |
2003 |
2004 |
2005 |
|
Lifetime |
48.8% |
49.0% |
47.8% |
46.1% |
45.7% |
44.8% |
|
Annual |
36.5 |
37.0 |
36.2 |
34.9 |
34.3 |
33.6 |
|
30-day |
21.6 |
22.4 |
21.5 |
21.2 |
19.9 |
19.8 |
|
Daily |
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.
|
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 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 movement4.
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 long-term 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 system5
and changes in the activity of nerve cells
containing dopamine6.
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
marijuana7.
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 nonsmokers8.
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 airways9.
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 cancers10.
Marijuana abuse also has the potential to promote
cancer of the lungs and other parts of the
respiratory tract because it contains irritants and
carcinogens9,11.
In fact, marijuana smoke contains 50 to 70 percent
more carcinogenic hydrocarbons than does tobacco
smoke12.
It also induces high levels of an enzyme that
converts certain hydrocarbons into their
carcinogenic form—levels that may accelerate the
changes that ultimately produce malignant cells13.
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 inhibited14.
In other studies, mice exposed to THC or related
substances were more likely than unexposed mice to
develop bacterial infections and tumors15,16.
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. Depression17,
anxiety17,
and personality disturbances18
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 off19,20,25.
Students who smoke marijuana get lower grades and
are less likely to graduate from high school,
compared with their nonsmoking peers21,22,23,24.
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 hours20.
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 weeks25.
Thus, some cognitive abilities may be restored in
individuals who quit smoking marijuana, even after
long-term heavy use.
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 pre-employment 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 use26.
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
health27.
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 stimuli28,
increased tremulousness, and a high-pitched cry,
which may indicate neurological problems in
development29.
During the preschool years, marijuana-exposed
children have been observed to perform tasks
involving sustained attention and memory more poorly
than nonexposed children do30,31.
In the school years, these children are more likely
to exhibit deficits in problem-solving skills,
memory, and the ability to remain attentive30.
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 anxiety32.
They also display increased aggression on
psychological tests, peaking approximately one week
after the last use of the drug33.
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 drug34.
(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
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 1835.
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
period36.
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 outcomes37.
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.
1 Results
from the 2004 National Survey on Drug Use and
Health: National Findings (Office of Applied
Studies, NSDUH Series H–27, DHHS Publication No. SMA
05–4061). Rockville, MD, 2004. NSDUH is an annual
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Health Services Administration. Copies of the latest
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for Alcohol and Drug Information at 800-729-6686.
2 These data are from the annual Drug Abuse Warning
Network, funded by the Substance Abuse and Mental
Health Services Administration, DHHS. The survey
provides information about emergency department
visits that are induced by or related to the use of
an illicit drug or the nonmedical use of a legal
drug. The latest data are available at 800-729-6686
or online at www.samhsa.gov.
3 These data are from the 2005 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.
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35 These data from the Treatment Episode Data Set (TEDS)
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