Marijuana is a green or gray mixture of dried, shredded flowers and
leaves of the hemp plant Cannabis sativa. There are over 200 slang terms
for marijuana including "pot," "herb," "weed," "boom," "Mary Jane," "gangster,"
and "chronic." It is usually smoked as a cigarette (called a joint or a nail)
or in a pipe or bong. In recent years, it has appeared in blunts. These are
cigars that have been emptied of tobacco and re-filled with marijuana, often in
combination with another drug, such as crack. Some users also mix marijuana
into foods or use it to brew tea. |
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The main active
chemical in marijuana is THC (delta-9-tetrahydrocannabinol). In 1988, it was
discovered that the membranes of certain nerve cells contain protein receptors
that bind 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. The short term effects of marijuana use include problems with
memory and learning; distorted |
perception;
difficulty in thinking and problem-solving; loss of coordination; and increased
heart rate, anxiety, and panic attacks.
Scientists have found that whether an individ ual has positive or
negative sensations after smoking marijuana can be influenced by heredity. A
recent study demonstrated that identical male twins were more likely than
nonidentical male twins to report similar responses to marijuana use,
indicating a genetic basis for their sensations. Identical twins share all of
their genes, and fraternal twins share about half. Environmental factors 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
would be different even for identical twins also were found to have an
important effect; however, it also was discovered that the twins' shared or
family environment before age 18 had no detectable influence on their response
to marijuana.
Health Hazards
Effects of Marijuana on the Brain
Researchers have found that THC changes the way in which sensory
information gets into and is acted on by the hippocampus. This is a component
of the brain's limbic system that is crucial for learning, memory, and the
integration of sensory experiences with emotions and motivations.
Investigations have shown that neurons in the information processing system of
the hippocampus and the activity of the nerve fibers are suppressed by THC. In
addition, researchers have discovered that learned behaviors, which depend on
the hippocampus, also deteriorate.
Recent research findings also indicate that long-term use of marijuana
produces changes in the brain similar to those seen after long-term use of
other major drugs of abuse.
Effects on the Lungs
Someone who smokes marijuana regularly may have many of the same
respiratory problems that tobacco smokers have. These individuals may have
daily cough and phlegm, symptoms of chronic bronchitis, and more frequent chest
colds. Continuing to smoke marijuana can lead to abnormal functioning of lung
tissue injured or destroyed by marijuana smoke.
Regardless of the THC content, the amount of tar inhaled by marijuana
smokers and the level of carbon monoxide absorbed are three to five times
greater than among tobacco smokers. This may be due to the marijuana users
inhaling more deeply and holding the smoke in the lungs.
Effects on Heart Rate and Blood
Pressure
Recent findings indicate that smoking marijuana while shooting up
cocaine has the potential to cause severe increases in heart rate and blood
pressure. In one study, experienced marijuana and cocaine users were given
marijuana alone, cocaine alone, and then a combination of both. Each drug alone
produced cardiovascular effects; when they were combined, the effects were
greater and lasted longer. The heart rate of the subjects in the study
increased 29 beats per minute with marijuana alone and 32 beats per minute with
cocaine alone. When the drugs were given together, the heart rate increased by
49 beats per minute, and the increased rate persisted for a longer time. The
drugs were given with the subjects sitting quietly. In normal circumstances, an
individual may smoke marijuana and inject cocaine and then do something
physically stressful that may significantly increase risks of overload on the
cardiovascular system.
Effects of Heavy Marijuana Use on Learning and Social
Behavior
A study of college students has shown that critical skills related to
attention, memory, and learning are impaired among people who use marijuana
heavily, even after discontinuing its use for at least 24 hours. Researchers
compared 65 "heavy users," who had smoked marijuana a median of 29 of the past
30 days, and 64 "light users," who had smoked a median of 1 of the past 30
days. After a closely monitored 19- to 24-hour period of abstinence from
marijuana and other illicit drugs and alcohol, the undergraduates were given
several standard tests measuring aspects of attention, memory, and learning.
Compared to the light users, heavy marijuana users made more errors and had
more difficulty sustaining attention, shifting attention to meet the demands of
changes in the environment, and in registering, processing, and using
information. The findings suggest that the greater impairment among heavy users
is likely due to an alteration of brain activity produced by
marijuana.
Longitudinal research on marijuana use among young people below
college age indicates those who used have lower achievement than the non-users,
more acceptance of deviant behavior, more delinquent behavior and aggression,
greater rebelliousness, poorer relationships with parents, and more
associations with delinquent and drug-using friends.
Research also shows more anger and more regressive behavior (thumb
sucking, temper tantrums) in toddlers whose parents use marijuana than among
the toddlers of non-using parents.
Effects on Pregnancy
Any drug of abuse can affect a mother's health during pregnancy, and
this is a time when she should take special care of herself. Drugs of abuse may
interfere with proper nutrition and rest, which can affect good functioning of
the immune system. Some studies have found that babies born to mothers who used
marijuana during pregnancy were smaller than those born to mothers who did not
use the drug. In general, smaller babies are more likely to develop health
problems.
A nursing mother who uses marijuana passes some of the THC to the baby
in her breast milk. Research indicates that the use of marijuana by a mother
during the first month of breast-feeding can impair the infant's motor
development (control of muscle movement).
Addictive Potential
A drug is addicting if it causes compulsive, often uncontrollable drug
craving, seeking, and use, even in the face of negative health and social
consequences. Marijuana meets this criterion. More than 120,000 people seek
treatment per year for their primary marijuana addiction. In addition, animal
studies suggest marijuana causes physical dependence, and some people report
withdrawal symptoms.
Extent of Use
Monitoring the Future Study (MTF)
The NIDA-funded MTF provides an annual assessment of drug use among
12th, 10th, and 8th grade students and young adults nationwide. After
decreasing for over a decade, marijuana use among students began to increase in
the early 1990s. From 1996 to 1997, use of marijuana at least once (lifetime
use) increased among 12th and 10th graders, continuing the trend seen in recent
years. The seniors' rate of lifetime marijuana use is higher than any year
since 1987, but all rates remain well below those seen in the late 1970s and
early 1980s. Past year and past month marijuana use did not change
significantly from 1996 to 1997 in any of the three grades, suggesting the
sharp increases of recent years may be slowing. Daily marijuana use in the past
month increased among 12th graders, but decreased among 8th graders; this
pattern of increases among older students and stable or declining rates among
younger students was found with several indicators in the 1997 MTF.
Percentage of 8th-Graders Who Have Used Marijuana:
Monitoring the Future Study
|
1991 |
1992 |
1993 |
1994 |
1995 |
1996 |
1997 |
Ever
Used |
10.2% |
11.2% |
12.6% |
16.7% |
19.9% |
23.1% |
22.6% |
Used in
Past Year |
6.2 |
7.2 |
9.2 |
13.0 |
15.8 |
18.3 |
17.7 |
Used in
Past Month |
3.2 |
3.7 |
5.1 |
7.8 |
9.1 |
11.3 |
10.2 |
Daily Use
in Past Month |
0.2 |
0.2 |
0.4 |
0.7 |
0.8 |
1.5 |
1.1 |
Percentage of 10th-Graders Who Have Used Marijuana:
Monitoring the Future Study
|
1991 |
1992 |
1993 |
1994 |
1995 |
1996 |
1997 |
Ever Used |
23.4% |
21.4% |
24.4% |
30.4% |
34.1% |
39.8% |
42.3% |
Used in Past Year |
16.5 |
15.2 |
19.2 |
25.2 |
28.7 |
33.6 |
34.8 |
Used in Past Month |
8.7 |
8.1 |
10.9 |
15.8 |
17.2 |
20.4 |
20.5 |
Daily Use in Past Month |
0.8 |
0.8 |
1.0 |
2.2 |
2.8 |
3.5 |
3.7 |
Percentage of 12th-Graders Who Have Used Marijuana
Monitoring the Future Study
|
1979 |
1985 |
1991 |
1992 |
1993 |
1994 |
1995 |
1996 |
1997 |
Ever Used |
60.4% |
54.2% |
36.7% |
32.6% |
35.3% |
38.2% |
41.7% |
44.9% |
49.6% |
Used in Past Year |
50.8 |
40.6 |
23.9 |
21.9 |
26.0 |
30.7 |
34.7 |
35.8 |
38.5 |
Used in Past Month |
36.5 |
25.7 |
13.8 |
11.9 |
15.5 |
19.0 |
21.2 |
21.9 |
23.7 |
Daily Use in Past Month |
10.3 |
4.9 |
2.0 |
1.9 |
2.4 |
3.6 |
4.6 |
4.9 |
5.8 |
Community Epidemiology Work Group
(CEWG)
The resurgence in marijuana use continues, especially among
adolescents, with rates of emergency department mentions of marijuana
increasing from 1994 to 1995 in 10 cities, the percentage of treatment
admissions increasing in 13 areas, and the National Institute of Justice's Drug
Use Forecasting (DUF) percentages increasing among juvenile arrests at numerous
sites. In several cities, such as Minneapolis/St. Paul, increasing treatment
figures have been particularly notable among juveniles. Two factors may be
contributing to the dramatic leap in adverse consequences: higher potency and
the use of marijuana mixed with or in combination with other dangerous
drugs.
National Household Survey on Drug Abuse
(NHSDA)
Marijuana remains the most commonly used illicit drug in the United
States. There were an estimated 2.4 million people who started using marijuana
in 1995. According to data from the 1996 NHSDA, more than 68.6 million
Americans (32 percent) 12 years of age and older have tried marijuana at least
once in their lifetimes, and almost 18.4 million (8.6 percent) had used
marijuana in the past year. In 1985, 56.5 million Americans (29.4 percent) had
tried marijuana at least once in their lifetimes, and 26.1 million (13.6
percent) had used marijuana within the past year. |