Marijuana refers to the dried leaves, flowers, stems, and seeds from the hemp plant
Cannabis sativa,
which contains the psychoactive (mind-altering) chemical
delta-9-tetrahydrocannabinol (THC), as well as other related compounds.
This plant material can also be concentrated in a resin called hashish
or a sticky black liquid called
hash oil.
Marijuana is the most common illicit drug used in the United States.
After a period of decline in the last decade, its use has been
increasing among young people since 2007, corresponding to a diminishing
perception of the drug’s risks that may be associated with increased
public debate over the drug’s legal status. Although the federal
government considers marijuana a Schedule I substance (having no
medicinal uses and high risk for abuse), two states have legalized
marijuana for adult recreational use, and 20 states have passed laws
allowing its use as a treatment for certain medical conditions (see “Is
Marijuana Medicine?”, below).
How is Marijuana Used?
Marijuana is usually smoked in hand-rolled cigarettes (joints) or in
pipes or water pipes (bongs). It is also smoked in blunts—cigars that
have been emptied of tobacco and refilled with a mixture of marijuana
and tobacco. Marijuana smoke has a pungent and distinctive, usually
sweet-and-sour, odor. Marijuana can also be mixed in food or brewed as a
tea.
THC's
chemical structure is similar to the brain chemical anandamide.
Similarity in structure allows drugs to be recognized by the body and to
alter normal brain communication
How Does Marijuana Affect the Brain?
When marijuana is smoked, THC rapidly passes from the lungs into the
bloodstream, which carries the chemical to the brain and other organs
throughout the body. It is absorbed more slowly when ingested in food or
drink.
However it is ingested, THC acts on specific molecular targets on
brain cells, called cannabinoid receptors. These receptors are
ordinarily activated by chemicals similar to THC that naturally occur in
the body (such as anandamide; see picture, above) and are part of a
neural communication network called the endocannabinoid system. This
system plays an important role in normal brain development and function.
The highest density of cannabinoid receptors is found in parts of the
brain that influence pleasure, memory, thinking, concentration, sensory
and time perception, and coordinated movement. Marijuana overactivates
the endocannabinoid system, causing the “high” and other effects that
users experience. These effects include altered perceptions and mood,
impaired coordination, difficulty with thinking and problem solving, and
disrupted learning and memory.
Marijuana also affects brain development, and when it is used heavily
by young people, its effects on thinking and memory may last a long
time or even be permanent. A recent study of marijuana users who began
using in adolescence revealed substantially reduced connectivity among
brain areas responsible for learning and memory. And a large long-term
study in New Zealand showed that people who began smoking marijuana
heavily in their teens lost an average of 8 points in IQ between age 13
and age 38. Importantly, the lost cognitive abilities were not fully
restored in those who quit smoking marijuana as adults. Those who
started smoking marijuana in adulthood did not show significant IQ
declines.
What Are the Other Health Effects of Marijuana?
Marijuana use may have a wide range of effects, particularly on cardiopulmonary and mental health.
Marijuana smoke is an irritant to the lungs, and frequent marijuana
smokers can have many of the same respiratory problems experienced by
tobacco smokers, such as daily cough and phlegm production, more
frequent acute chest illness, and a heightened risk of lung infections.
One study found that people who smoke marijuana frequently but do not
smoke tobacco have more health problems and miss more days of work than
those who don’t smoke marijuana, mainly because of respiratory
illnesses. It is not yet known whether marijuana smoking contributes to
risk for lung cancer.
Is Marijuana Medicine?
Many have called for the legalization of marijuana to treat
conditions including pain and nausea caused by HIV/AIDS, cancer, and
other conditions, but clinical evidence has not shown that the
therapeutic benefits of the marijuana plant outweigh its health risks.
To be considered a legitimate medicine by the FDA, a substance must have
well-defined and measurable ingredients that are consistent from one
unit (such as a pill or injection) to the next. As the marijuana plant
contains hundreds of chemical compounds that may have different effects
and that vary from plant to plant, and because the plant is typically
ingested via smoking, its use as a medicine is difficult to evaluate.
However, THC-based drugs to treat pain and nausea are already FDA
approved and prescribed, and scientists continue to investigate the
medicinal properties of other chemicals found in the cannabis plant—such
as cannabidiol, a non-psychoactive cannabinoid compound that is being
studied for its effects at treating pain, pediatric epilepsy, and other
disorders. For more information, see
DrugFacts - Is Marijuana Medicine?
Marijuana also raises heart rate by 20-100 percent shortly after
smoking; this effect can last up to 3 hours. In one study, it was
estimated that marijuana users have a 4.8-fold increase in the risk of
heart attack in the first hour after smoking the drug. This risk may be
greater in older individuals or in those with cardiac vulnerabilities.
A number of studies have linked chronic marijuana use and mental
illness. High doses of marijuana can produce a temporary psychotic
reaction (involving hallucinations and paranoia) in some users, and
using marijuana can worsen the course of illness in patients with
schizophrenia. A series of large studies following users across time
also showed a link between marijuana use and later development of
psychosis. This relationship was influenced by genetic variables as well
as the amount of drug used, drug potency, and the age at which it was
first taken—those who start young are at increased risk for later
problems.
Associations have also been found between marijuana use and other
mental health problems, such as depression, anxiety, suicidal thoughts
among adolescents, and personality disturbances, including a lack of
motivation to engage in typically rewarding activities. More research is
still needed to confirm and better understand these linkages.
Marijuana use during pregnancy is associated with increased risk of
neurobehavioral problems in babies. Because THC and other compounds in
marijuana mimic the body’s own endocannabinoid chemicals, marijuana use
by pregnant mothers may alter the developing endocannabinoid system in
the brain of the fetus. Consequences for the child may include problems
with attention, memory, and problem solving.
Additionally, because it seriously impairs judgment and motor
coordination, marijuana contributes to risk of injury or death while
driving a car. A recent analysis of data from several studies found that
marijuana use more than doubles a driver’s risk of being in an
accident. The combination of marijuana and alcohol is worse than either
substance alone with respect to driving impairment
Rising Potency
The amount of THC in marijuana samples confiscated by police has
been increasing steadily over the past few decades. In 2012, THC
concentrations in marijuana averaged close to 15 percent, compared to
around 4 percent in the 1980s. For a new user, this may mean exposure to
higher concentrations of THC, with a greater chance of an adverse or
unpredictable reaction. Increases in potency may account for the rise in
emergency department visits involving marijuana use. For frequent
users, it may mean a greater risk for addiction if they are exposing
themselves to high doses on a regular basis. However, the full range of
consequences associated with marijuana's higher potency is not well
understood. For example, experienced users may adjust their intake in
accordance with the potency or they may be exposing their brains to
higher levels overall, or both.
Is Marijuana Addictive?
Contrary to common belief, marijuana is addictive. Estimates from
research suggest that about 9 percent of users become addicted to
marijuana; this number increases among those who start young (to about
17 percent, or 1 in 6) and among people who use marijuana daily (to
25-50 percent).
Long-term marijuana users trying to quit report withdrawal symptoms
including irritability, sleeplessness, decreased appetite, anxiety, and
drug craving, all of which can make it difficult to abstain. Behavioral
interventions, including cognitive-behavioral therapy and motivational
incentives (i.e., providing vouchers for goods or services to patients
who remain abstinent) have proven to be effective in treating marijuana
addiction. Although no medications are currently available, recent
discoveries about the workings of the endocannabinoid system offer
promise for the development of medications to ease withdrawal, block the
intoxicating effects of marijuana, and prevent relapse.
How Does Marijuana Affect a User’s Life?
Research shows marijuana may cause problems in daily life or make a
person's existing problems worse. Heavy marijuana users generally report
lower life satisfaction, poorer mental and physical health, more
relationship problems, and less academic and career success compared to
non-marijuana-using peers. For example, marijuana use is associated with
a higher likelihood of dropping out of school. Several studies also
associate workers' marijuana smoking with increased absences, tardiness,
accidents, workers' compensation claims, and job turnover.
Learn More
For information on NIDA's marijuana research, click
here.
For additional information on marijuana and marijuana abuse, please see NIDA's
Research Report Marijuana Abuse
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