Marijuana is the most commonly used 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. Use also might
include mixing marijuana in food or brewing it 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®, Juicy Fruit®, Afghani #1®, and a number of Skunk
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
There were an estimated 2.6 million new marijuana users
in 2001. This number is similar to the numbers of new users each year
since 1995, but above the number in 1990 (1.6 million). In 2002, over
14 million Americans age 12 and older used marijuana at least once in
the month prior to being surveyed, and 12.2 percent of past year marijuana
users used marijuana on 300 or more days in the past 12 months. This
translates into 3.1 million people using marijuana on a daily or almost
daily basis over a 12-month period.
The percentage of youth age 12 to 17 who had ever used marijuana declined
slightly from 2001 to 2002 (21.9 to 20.6 percent). Among adults age
18 to 25, the rate increased slightly from 53.0 percent to 53.8 percent
in 2002. The percentage of young adults age 18 to 25 who had ever used
marijuana was 5.1 percent in 1965, but increased steadily to 54.4 percent
in 1982. Although the rate for young adults declined somewhat from 1982
to 1993, it did not drop below 43 percent and actually increased to
53.8 percent by 2002.
Forty-two percent of youth age 12 or 13 and 24.1 percent age 16 or 17
perceived smoking marijuana once a month as a great risk. Slightly more
than half of youth age 12 to 17 indicated that it would be fairly or
very easy to obtain marijuana, but only 26.0 percent of 12- or 13-year-olds
indicated the same thing. However, 79.0 percent of those age 16 or 17
indicated that it would be fairly or very easy to obtain marijuana.
Prevalence of lifetime, past year, and past month marijuana use declined
among students in 8th, 10th, and 12th grades in 2003. However, the declines
in 12-month prevalence reached statistical significance only in 8th-graders;
past year use has declined by nearly one-third since 1996. All three
grades showed an increase in perceived risk for regular marijuana use.
This finding represents a welcome turnaround in this perception, which
has been in decline in all grades over the past 1 or 2 years.
In 2002, marijuana was the third most commonly abused drug mentioned
in drug-related hospital emergency department (ED) visits in the continental
United States. Marijuana mentions rose significantly (24%) from 2000
to 2002, but showed no significant increase since 2001. Taking changes
in population into account, marijuana mentions increased 139 percent
from 1995 to 2002.
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 movement.
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 use indicate some changes in the brain similar
to those seen after long-term use of other major drugs of abuse. 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 and changes in the activity of nerve cells containing dopamine.
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 a users risk of heart
attack more than quadruples in the first hour after smoking marijuana.
The researchers suggest that such an effect might occur from marijuanas
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. Many of the extra sick days
among the marijuana smokers in the study were for respiratory illnesses.
Even infrequent 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 illness, a heightened risk of lung infections, and a greater
tendency to obstructed airways. Smoking marijuana increases the likelihood
of developing cancer of the head or neck, and the more marijuana smoked
the greater the increase. A study comparing 173 cancer patients and
176 healthy individuals produced strong evidence that marijuana smoking
doubled or tripled the risk of these cancers.
Marijuana use also 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 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 formlevels 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 tobacco.
Other Health Effects
Some of marijuanas adverse health effects may occur
because THC impairs the immune systems 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 and tumors.
Effects of Heavy Marijuana Use on Learning and Social Behavior
Depression, anxiety, and personality disturbances have
been associated with marijuana use. Research clearly demonstrates that
marijuana has potential to cause problems in daily life or make a persons
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. Moreover, research has shown that marijuanas
adverse impact on memory and learning can last for days or weeks after
the acute effects of the drug wear off.
Students who smoke marijuana get lower grades and are less likely to
graduate from high school, compared with their non-smoking peers. A
study of 129 college students found that, for 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
every day may be functioning at a reduced intellectual level all of
More recently, the same researchers showed that the ability of a group
of long-term heavy marijuana users to recall words from a list remained
impaired for a week after quitting, but returned to normal within 4
weeks. Thus, it is possible that some cognitive abilities may be restored
in individuals who quit smoking marijuana, even after long-term heavy
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 of municipal workers
found that those who used marijuana on or off the job reported more
withdrawal behaviorssuch as leaving work without permission,
daydreaming, spending work time on personal matters, and shirking tasksthat
adversely affect productivity and morale. In another study, marijuana
users reported that use of the drug impaired several important measures
of life achievement including cognitive abilities, career status, social
life, and physical and mental health.
Long-term marijuana use can lead to addiction for some
people; that is, they use 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 using the drug. People trying to quit report irritability, sleeplessness,
and anxiety. They also display increased aggression on psychological
tests, peaking approximately one week after the last use of the drug.
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 non-identical male twins to report similar responses
to marijuana use, indicating a genetic basis for their response to the
drug. (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.
Treating Marijuana Problems
The latest treatment
data indicate that, in 2000, marijuana was the primary drug of abuse
in about 15 percent (236,638) of all admissions to treatment facilities
in the United States. Marijuana admissions were primarily male (76 percent),
White (57 percent), and young (46 percent under 20 years old). Those
in treatment for primary marijuana use had begun use at an early age;
56 percent had used it by age 14 and 92 percent had used it by 18.
One study of adult marijuana users 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 use, both
treatments sought to help patients devise avoidance strategies. Use,
dependence symptoms, and psychosocial problems decreased for at least
1 year following both treatments; about 30 percent of users were abstinent
during the last 3-month followup period.
Another study suggests that giving patients vouchers that they can redeem
for goodssuch as movie passes, sporting equipment, or vocational
trainingmay further improve outcomes.
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
Find this information and more at www.drugabuse.gov