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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 individual 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 brains 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 mothers 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 infants 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 Justices 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.
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