Marijuana, mixture of leaves, stems, and flowering tops of the Indian hemp plant Cannabis sativa, smoked or eaten for its hallucinogenic and pleasure-giving effects. The psychoactive ingredient of marijuana, tetrahydrocannabinol (THC), is concentrated in the flowering tops; hashish, a drug prepared from the plant resin, has about eight times more THC than marijuana. Marijuana grows throughout temperate regions, with the more potent varieties produced in dry, hot, upland climates. Except for limited medical purposes, cultivating marijuana is illegal in all but a few countries.
Known in Central Asia and China as early as 3000 BC, marijuana was used as a folk medicine. About 1900 it started to be used as a pleasure-inducing drug, and by the 1960s and 70s its use was widespread among students, becoming, after alcohol, the second most popular drug. Although marijuana has not been proven to be physically addicting, and no physical withdrawal symptoms occur when its use is discontinued, psychological dependence does develop. Many users describe two phases of marijuana intoxication: initial stimulation, giddiness, and euphoria, followed by sedation and pleasant tranquility. Mood changes are often accompanied by altered perceptions of time and space and of one s bodily dimensions. The thinking processes become disrupted by fragmentary ideas and memories. Many users report increased appetite, heightened sensory awareness, and pleasure. Negative effects can include confusion, acute panic reactions, anxiety attacks, fear, a sense of helplessness, and loss of self-control.
Chronic marijuana users are said to develop an amotivational syndrome characterized by passivity, decreased motivation, and preoccupation with drug taking. The relationship of this syndrome to marijuana use, however, has not been established. Like alcohol intoxication, marijuana intoxication impairs reading comprehension, memory, speech, problem-solving ability, and reaction time. The effects on the intellect of long-term use are unknown. Consistent evidence that marijuana induces or causes brain damage does not exist. Medical research has indicated that the drug is effective in relieving some of the symptoms of glaucoma and in treating the nausea induced by cancer chemotherapy and radiation treatments