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Indian hemp plant (Cannabis sativa) or the crude drug made of its dried and crushed leaves or flowers. The active ingredient is tetrahydrocannabinol (THC). Also called pot, grass, and weed, the drug has long been used as a sedative or analgesic; it was in use in China by the 3rd millennium BC and had reached Europe by AD 500. Today it is used worldwide, though it has been generally illegal at least since the International Opium Convention of 1925. Its psychological and physical effects, including mild euphoria and alterations in vision and judgment, vary with strength and amount consumed, the setting, and the user's experience. Chronic use is not physically habit-forming but may be mildly psychologically habit-forming. Marijuana has been shown to be medically therapeutic for patients with glaucoma, AIDS, and the side effects of chemotherapy; in 2001 Canada became the first country to legalize the use of marijuana by people with terminal illnesses and chronic conditions. Supporters of legalization claim that it is a more benign drug than alcohol; opponents contend that it is addictive and leads to use of more serious drugs. A resin from the plant is the source of hashish.
This entry comes from Encyclopædia Britannica Concise. For the full entry on marijuana, visit Britannica.com.