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Marijuana
Introduction
Health
Behavior
Pregnancy
Epidemiology |
Marijuana
Introduction
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, marijuana has appeared in blunts, which are cigars that have
been emptied of tobacco and refilled with marijuana, often in combination with
another drug, such as crack. Some users also mix marijuana into foods or use it
to brew tea.
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 non-identical 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 differentiate identical twins' experiences 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 processed by the hippocampus. The hippocampus 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 in this region are suppressed by THC. In
addition, researchers have discovered that learned behaviors, which depend on
the hippocampus, also deteriorate via this mechanism.
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 as tobacco
smokers. 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 and because marijuana smoke is unfiltered.
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 the risk of overloading 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. These 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 marijuana 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, making it a time when expectant
mothers should take special care of themselves. 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 enter 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
1998 to 1999, 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 1998 to 1999 in any
of the three grades, suggesting the sharp increases of recent years may be
slowing. Daily marijuana use in the past month increased slightly among all
three grades as well.
Community
Epidemiology Work Group (CEWG)**
In 1998, marijuana
indicators continued an upward trend in most of the 20 CEWG metropolitan areas.
Rates of emergency department men-tions of marijuana increased significantly in
seven sites, with the largest increases occurring in Dallas (emergency room
mentions increased to 63.9 percent), Boston (to 44.1 percent), Denver (to 40
percent), San Diego (to 35.1 percent), and Atlanta (to 31.7 percent). The
highest percent increase in emergency room mentions comparing the first half of
1997 and the first half of 1998 was among 12- to 17-year olds.
Treatment
data for primary abuse of marijuana increased in six CEWG sites and remained
stable elsewhere. Marijuana treatment admissions were highest in Denver (41
percent of all admissions), Miami (30 percent), New Orleans (22 percent), and
Minneapolis/ St. Paul (20 percent). Half of the treatment admissions for
marijuana in Minneapolis/St. Paul were under age 18.
In
six of the CEWG sites, juvenile arrestees testing positive for marijuana ranged
from a low of 40.3 percent in St. Louis to a high of 63.7 percent in Phoenix.
More than 50 percent of juvenile arrestees in Los Angeles, Denver, and
Washington, D.C. tested positive for marijuana, and 48.9 percent in San Diego.
Among all arrestees, Seattle was the only site where women were more likely than
men (37.9 percent vs. 35.4 percent) to test positive for marijuana.
National
Household Survey on Drug Abuse (NHSDA)***
Marijuana remains the most commonly used illicit drug in the United States.
There were an estimated 2.1 million people who started using marijuana in 1998.
According to data from the 1998 NHSDA, more than 72.0 million Americans (33
percent) 12 years of age and older have tried marijuana at least once in their
lifetimes, and almost 18.7 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.
This
information is available courtesy of the NIDA.
It is in the public domain and can be downloaded, reproduced, or copied
without permission. For more information go to http://www.nimh.nih.gov/practitioners/patinfo.cfm
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