Marijuana is a greenish-gray mixture of the dried, shredded leaves, stems, seeds, and flowers of Cannabis sativa, the hemp plant. Most users smoke marijuana in hand-rolled cigarettes. The major active chemical in marijuana is delta-9-tetrahydro-cannabinol (THC), which causes the mind-altering effects of marijuana intoxication. Between 1980 and 1997, the amount of THC in marijuana available in the United States significantly increased. In 1999 more than 2 million Americans used marijuana for the first time; two-thirds of them were between the ages of 12 and 17. The marijuana that is available today can be five times more potent than the marijuana of the 1970's. During intoxication, marijuana impairs short-term memory, attention, judgment, and other cognitive functions, as well as coordination and balance. The heart rate increases. Further, memory and learning skills can be impaired beyond the intoxication period but may not be permanent. The cumulative, potentially permanent effects of the chronic abuse of marijuana are addiction; chronic cough, bronchitis, and emphysema; and increased risk of cancer of the head, neck, and lungs. Treatment programs for marijuana abuse are rare, partly because many who use marijuana do so in combination with other drugs, such as cocaine and alcohol. One study of adult marijuana users found comparable benefits from a 14-session cognitive-behavioral group treatment and a 2-session individual treatment that included motivational interviewing and advice on ways to reduce marijuana use. 24 references