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Marijuana is the common name for the drug obtained from the hemp plant, Cannabis sativa. Hemp is a tall annual plant that can grow in almost any climate. Native to central and western Asia, hemp is one of the oldest crops cultivated by humans. Hemp's most common agricultural use has been as a source of linen, rope, canvas, and paper.

Hemp contains more than 400 chemicals. The main psychoactive (affecting the mind or behavior) chemical is tetrahydrocannabinol, commonly referred to as THC. For over 3,000 years, the dried ground leaves, flowers, and stems of the plant have been smoked, eaten, chewed, or brewed as a medicine to relieve symptoms of illness. From the seventeenth to the early twentieth century, marijuana was considered a household drug useful for...