A preparation of the dried leaves, flowers, stems and seeds of the hemp plant Cannabis sativa, which contains the psychoactive drug tetrahydrocannabinol (THC).
Marijuana is the most noted name among cannabinoid drugs, although other formspan s of cannabis are available. Cannabis is the most cultivated and most Page 710 | Top of Articleused or abused psychoactive drug around the world. Its many forms have been used by humans for centuries, including medical use by early Greek and Roman civilizations. The psychoactive or mind-altering substance in cannabis is tetrahydrocannabinol, or THC, known chemically as delta-9-tetrahydrocannabinol. Marijuana is prepared from the dried leaves, flowers, stems and seeds of the cannabis or hemp plant, forming a complex botanical drug that contains about 100 cannabinoids among a total of 500 chemical constituents. Hashish is another form a cannabis, a dried resinous substance obtained from the leaves of unpollinated female cannabis plants, and hashish oil is obtained from these leaves by solvent extraction. Hashish oil is a concentrate of cannabinoids that is more potent than marijuana. Marijuana and hashish are usually smoked, a habit termed “pot smoking.” These drugs may also be ingested orally, and are some times added to food or beverages. Synthetic forms of delta-9-THC known as synthetic cannabinoid receptor agonists consist of cannabinoids sprayed on herbs and are sold as herbal smoking blends or“natural highs,” with effects similar to those of marijuana.
Among the world's total population, about 147 million people or 2.5% of the population consume cannabis in some form. In the United States, marijuana use became widespread among young people in the 1960s, consistent with rapid growth of pot-smoking globally. By 1979, 50 million young adults in the U.S. between the ages of 18 and 25 had smoked marijuana at least once, representing about 68% of this age group. In the late 1980s, admitted one-time use of marijuana had decreased to about 50–60% of people between the ages of 21 and 29. A 2013 National Survey on Drug Use and Health showed that marijuana was used by 81% of habitual users of illicit drugs and was the only drug used by 65% of this population. In 2014, 12% of eighth graders studied self-reported marijuana Page 711 | Top of Articleuse during the previous year and 6.5% reported current use. Generally, usuage is still widespread among adolescents and young adults in developed countries. This is believed due to a steady decline in theerceptions of risk associated with the drug, which is considered to be the result of increasing debate about legalizing the drug or relaxing restrictions. Low prices for the drug are also associated with periods of abuse.
As of June 2015, marijuana had been legalized in some form in 23 U.S. states and the District of Columbia, but only 4 states (Alaska, Colorado, Oregon, and Washington) have legalized it for recreational use. Some states have decriminalized possession of small amounts of marijuana, typically one ounce or less. Other states have legalized only “medical marijuana” for limited use in treating nausea and vomiting associated with chemotherapy and AIDS, as an appetitite stimulant, as an anticonvulsive or antispasmodic in certain nervous system disorders such as epilepsy, and as a treatment for glaucoma.
The effects of marijuana vary from individual to individual, depending on the physical and psychological condition of the user, the amount of THC actually consumed, and the purity of the drug preparation. Receptors for THC have been discovered in the brain, together with a naturally occurring cannabinoid neurotransmitter called anandamide that binds the chemical to its receptors. Technically, marijuana is classified as a hallucinogen, but its effects are usually much milder than those of other drugs in that class, such as LSD, mescaline, and psilocybin. When a marijuana cigarette is inhaled, THC reaches its highest concentration in the blood within a half hour, is absorbed by the brain and other organs, and can affect consciousness for several hours. THC can remain stored in body fat for several weeks but without further hallucinogenic effects. Marijuana users describe feelings of euphoria, selfconfidence, reduced inhibition, relaxation, and a floating sensation. Feelings of giddiness and mild feelings of paranoia are also common. Physiological effects include increases in pulse and heart rates, reddened eyes, dryness of the mouth, and an increased appetite, particularly for sweets. The initial euphoric feelings after ingesting marijuana are generally followed by sleepiness. Although marijuana has been known to produce psychological dependence, extensive research has shown that chemical dependence or physical dependence is negligible and withdrawal from the drug does not pose medical problems. Although few serious health risks are associated with using the drug, chronic use is associated with negative effects.
Documented negative effects of marijuana use include impairment of perception, sensory motor coordination, and short-term memory. For these reasons, individuals are cautioned not to operate machinery or motor vehicles after using the drug. Individuals who are subject to anxiety or panic attacks are also cautioned not to use the drug as these may be accentuated. Consistent marijuana use has also been linked to immune system dysfunction, lowered testosterone levels in males, and chromosome damage. Marijuana may affect the developing fetus if used by pregnant women. Long-term marijuana smokers display respiratory inflammation and related illnesses similar to tobacco smokers. In research on rats, THC has been found to cause structural and functional changes in the hippocampus, a part of the brain that is important in memory. Studies in human adolescents have also revealed that regular users had impaired neural connectivity in parts of the brain responsible for memory, learning, and impulse control. Psychological effects associated with chronic use of marijuana include a loss of ambition known as amotivational syndrome. Controversy surrounds the physical and psychological risks of short-term and long-term use/abuse of cannabis and researchers continue to explore its effects and its therapeutic potential.
See also Cannabis and cannabis disorders.
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Bechtold, J., Simpson, T., White, H.R., Pardini, D.“Chronic adolescent marijuana use as a risk factor for physical and mental health problems in young adult men.” Psy-chology Addictive Behaviors. (Aug 2015)Epub ahead of print.
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