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Hemp, or Cannabis sativa, is a tall, annual plant that thrives in temperate and subtropical climates. It is native to central and western Asia, and is one of the oldest cultivated plants. The word "hemp" is derived from the old English word "hanf," and refers to both the plant and the long fibers that are processed from its stems. The most common use of hemp has been as a source of fiber for manufacturing rope, canvas, other textiles, and paper. Hemp contains more than 400 biochemicals, and has been used for medicinal purposes for at least 3,000 years. Even today, it is useful as a treatment for cancer and AIDS patients, because its stimulatory effect on the appetite can help victims of these diseases to avoid weight loss. During the twentieth century hemp gained notoriety as the source of marijuana, a psychoactive drug banned in most countries.

Hemp is a dioecious plant, meaning there are separate male and female plants. It is an annual, herbaceous plant that can grow as tall as 10–20 ft (3–6 m). Hemp can be cultivated in a wide range of climates having adequate amounts of sun and moisture during the summer. It has a relatively short growing season, and, in the Northern Hemisphere, is planted in May and harvested in September. As hemp grows it improves soil quality somewhat, and reduces the abundance of weeds by casting a dense shade over the ground surface.

Hemp has been grown for at least 5,000 years to obtain its stem fibers for weaving cordage and textiles. Its fibers can be used for manufacturing rope, canvas, and other materials. Its seeds can be pressed for oil, which is used for making paint, heating and lubricating oils, animal feed, and pharmaceutical products. The plant also produces a sap rich in silica, which can be used for making abrasives.

For centuries, hemp was the largest cash crop in the world. As recently as 1941, U.S. farmers were encouraged by the federal government to grow hemp, because of the need for its fibers to make rope, parachutes, backpacks, hoses, and other necessities during World War II.

The cultivation of hemp has been outlawed in the United States and many other countries because its flowering buds, and to a lesser degree its foliage, are the source of the drug marijuana. The buds produce a yellow resin that contains various cannabinoid chemicals. Of these, delta-9-tetrahydrocannabinol, or THC, has the most psychoactive activity. THC combines with receptor sites in the human brain to cause drowsiness, increased appetite, giddiness, hallucinations, and other psychoactive effects. Although the causative mechanisms are not fully known, current research indicates that THC ingestion results in THC binding to receptor sites associated with measurable memory loss. Other studies correlate THC binding to receptors in the cerebellum and correlated decreases in motor coordination and/or the ability to maintain balance.

Plant breeders have now produced varieties of hemp with concentrations of THC that are too low for the plants to be used as a medicine or recreational drug. In Canada and many other countries, permits are being granted to allow farmers to grow low-THC hemp as a source of valuable fiber. Although United States Federal law prohibits hemp growth, as of 2002 eight states had passed state legislation authorizing industrial hemp research.

In 2002, a United States federal appeals court blocked a Drug Enforcement Administration (DEA) rule that attempted to ban food made with hemp. Prior to the ruling the DEA—relying on the Controlled Substances Act—banned food products containing tetrahydrocannabinol (THC). At press, an appeal was pending.

See also Natural fibers.



Bosca, I., and M. Karus. The Cultivation of Hemp: Botany, Varieties, Cultivation, and Harvesting. Hemptech Pub., 1998.

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