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marijuana or marihuana, drug obtained from the flowering tops, stems, and leaves of the hemp plant, Cannabis sativa (see hemp) or C. indica; the latter species can withstand colder climates. It is one of the most commonly used drugs in the world, following only caffeine, nicotine, and alcoholic beverages in popularity. In the United States, where it is usually smoked, it also has been called weed, grass, pot, or reefer.

The Plant

C. sativa grows as a common weed in many parts of the world, and drug preparations vary widely in potency according to climate, cultivation, and method of preparation. Mexico, Paraguay, and the United States are the top marijuana-producing nations worldwide. C. indica is a shorter, hardier variety with rounded blue-green leaves, grown in Afghanistan for hashish. Most marijuanas grown in the United States since the late 1980s are hybrids of the two and yield a much more potent product than the marijuana of the past. The resin found on flower clusters and top leaves of the female plant is the most potent drug source and is used to prepare hashish, the highest grade of cannabis. The bud of the female plant, called sinsemilla, is the part most often smoked as marijuana.

The Drug

The effects of marijuana vary with its strength and dosage and with the state of mind of the user. Typically, small doses result in a feeling of well-being. The intoxication lasts two to three hours, but accompanying effects on motor control last much longer. High doses can cause tachycardia, paranoia, and delusions. Although it produces some of the same effects as hallucinogens like LSD and mescaline (heightened sensitivity to colors, shapes, music, and other stimuli and distortion of the sense of time), marijuana differs chemically and pharmacologically.

The primary active component of marijuana is delta-9-tetrahydrocannabinol (THC), although other cannabinol derivatives are also thought to be intoxicating. Synthetic cannabinoids, which mimic the effects of THC, are the active components in so-called synthetic marijuana (see designer drug). In 1988 scientists discovered receptors that bind THC on the membranes of nerve cells. They reasoned that the body must make its own THC-like substance. The substance, named anandamide, was isolated from pig brains in 1992 by an American pharmacologist, William A. Devane.

Marijuana lowers testosterone levels and sperm counts in men and raises testosterone levels in women. In pregnant women it affects the fetus and results in developmental difficulties in the child. There is evidence that marijuana affects normal maturation of preadolescent and adolescent users and that it affects short-term memory and comprehension. Heavy smokers often sustain lung damage from the smoke and contaminants. Regular use can result in dependence.

The Legalization Question

With the increase in the number of middle-class users in the 1960s and 1970s, there came a somewhat greater acceptance of the view that marijuana should not be considered in the same class as narcotics and that U.S. marijuana laws should be relaxed. The Drug Abuse Prevention Act of 1970 eased federal penalties somewhat, and 11 states decriminalized possession. However, in the late 1980s many states rewrote their drug laws and imposed stricter penalties. Beginning in 1996, however, a series of states began enacting medical marijuana laws (see below). In 2012 voters in the states of Colorado and Washington approved the legalization of the private use and possession of small amounts of marijuana; since then 13 more states, the District of Columbia, and two territories have taken similar steps. Opponents of easing marijuana laws have asserted that it is an intoxicant less controllable than alcohol, that society does not need another widely used intoxicant, and that the United States should not act to weaken UN policies, which are opposed to the use of marijuana for other than possible medical purposes. In 2013, Uruguay became the first nation to legalize the growing, selling, and use of marijuana, a move it undertook in part in an attempt to undermine drug cartels. Uruguay's legalization, which was a source of controversy in the country, also was critized by international authorities for contravening treaties to which Uruguay was a party. Canada became the second nation to legalize fully marijuana in 2018.

Medical Uses

Historically, marijuana has been used since ancient times in non-Western medicine to treat a range of conditions; the preparation used and the manner in which has been given has varied. In the 1800s its use in treatment of a number of conditions was explored and documented by some Western physicians as well, and it also was an ingredient in patent medicines. In more recent times, controversy has surrounded the medical use of marijuana, with proponents saying it is useful for treating pain and the nausea and vomiting that are side effects of cancer chemotherapy, for restoring the appetite in people with AIDS, and for treating anxiety. Its active ingredient, THC, was synthesized in 1966 and approved by the U.S. Food and Drug Administration in 1985; synthetic THC is available by prescription in pill form as dronabinol (Marinol) and nabilone (Cesamet). Proponents of medical marijuana say it is not as effective as the herb and is more expensive. In addition to THC, another cannibis derivative (or cannabinoid), cannabidiol (CDB), is an anti-inflammatory and antioxidant and also moderates THC's psychoactive effects.

A 1999 U.S.-government-sponsored study by the Institute of Medicine found that marijuana appeared beneficial for certain medical conditions, such as nausea caused by chemotherapy and wasting caused by AIDS. Because of the toxicity of marijuana smoke, however, it was hoped that further research might lead to development of new delivery systems, such as bronchial inhalers. A number of studies since 1999 have shown that smoked marijuana has pain-reducing effects when compared with marijuana stripped of its cannabinoids.

The Office of National Drug Control Policy has opposed legalization of the medical use of marijuana, citing law enforcement issues and the possibility that some would use it as a pretext to sell marijuana for nonmedical use, and the FDA said in 2006 that, despite the 1999 report, that marijuana “has no accepted or proved use in the United States.” Proponents, disregarding the law, have set up networks for the distribution of the drug to people who they judge will be helped by it and continue to lobby for its legalization for medical use. In 1996 California enacted the first state law permitting the use of marijuana for medical reasons; most states now have approved some sort of medical marijuana legislation. As a result of a Supreme Court ruling in 2005, however, these laws do not protect medical users with a prescription from federal prosecution. In 2009 the U.S. attorney general ordered that federal prosecutors not focus on persons who clearly comply with state medical marijuana laws, but federal law enforcement officials have moved to close many so-called marijuana dispensaries despite compliance, arguing in part that many prescriptions for marijuana are not justified medically. Another, lower court ruling permits doctors to discuss medical use of marijuana with their patients but forbids them to help patients obtain the drug. Thirty countries permit the medical use of the drug.

History of Marijuana Use

Marijuana has been used as an agent for achieving euphoria since ancient times; it was described in a Chinese medical compendium traditionally considered to date from 2737 B.C. It also has a long history of use as a medicinal herb. Its use spread from China to India and then to N Africa and reached Europe at least as early as A.D. 500. A major crop in colonial North America, marijuana (hemp) was grown as a source of fiber. It was extensively cultivated during World War II, when Asian sources of hemp were cut off.

Marijuana was listed in the United States Pharmacopeia from 1850 until 1942 and was prescribed for various conditions including labor pains, nausea, and rheumatism. Its use as an intoxicant was also commonplace from the 1850s to the 1930s. A campaign conducted in the 1930s by the U.S. Federal Bureau of Narcotics (now the Bureau of Narcotics and Dangerous Drugs) sought to portray marijuana as a powerful, addicting substance that would lead users into narcotics addiction. It is still considered a “gateway” drug by some authorities. In the 1950s it was an accessory of the beat generation; in the 1960s it was used by college students and “hippies” and became a symbol of rebellion against authority.

The Controlled Substances Act of 1970 classified marijuana along with heroin and LSD as a Schedule I drug, i.e., having the relatively highest abuse potential and no accepted medical use. Most marijuana at that time came from Mexico, but in 1975 the Mexican government agreed to eradicate the crop by spraying it with the herbicide paraquat, raising fears of toxic side effects. Colombia then became the main supplier. The “zero tolerance” climate of the Reagan and Bush administrations (1981–93) resulted in passage of strict laws and mandatory sentences for possession of marijuana and in heightened vigilance against smuggling at the southern borders. The “war on drugs” thus brought with it a shift from reliance on imported supplies to domestic cultivation (particularly in Hawaii and California).

Beginning in 1982 the Drug Enforcement Administration turned increased attention to marijuana farms in the United States, and there was a shift to the indoor growing of plants specially developed for small size and high yield. After over a decade of decreasing use, marijuana smoking began an upward trend once more in the early 1990s, especially among teenagers, but by the end of the decade this upswing had leveled off well below former peaks of use. With the legalization of medical and recreational marijuana use in a number of states in the 21st cent., use has again increased. At the same time, the potency of the marijuana being used has also increased.


See J. S. Hochman, Marijuana and Social Evolution (1972); E. Marshal, Legalization (1988); M. S. Gold, Marijuana (1989); L. Grinspoon and B. J. Bakalar, Marijuana: The Forbidden Medicine (1995); publications of the Drugs & Crime Data Center and Clearinghouse, the Bureau of Justice Statistics Clearinghouse, and the National Clearinghouse for Alcohol and Drug Information.

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The Spanish name for the dried leaves and flowering tops of the hemp plant (Cannabis sativa), which have narcotic ingredients and are smoked in cigarettes. Also spelled marihuana.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.


, marihuana
1. the dried leaves and flowers of the hemp plant, used for its euphoric effects, esp in the form of cigarettes
2. another name for hemp (the plant)
Collins Discovery Encyclopedia, 1st edition © HarperCollins Publishers 2005