The common name of a small number of varieties of Cannabis sativa, or Indian hemp plant, which contain tetrahydrocannabinol (THC), a psychoactive drug.

Cannabis, in the form of marijuana, hashish (a dried resinous material that seeps from cannabis leaves and is more potent than marijuana), or other cannabinoids, is probably the most often used illegal substance in the world. In the United States, marijuana use became widespread among young people in the 1960s. By 1979, 68 percent of young adults between the ages of 18 and 25 had experimented with it at least once, and it was reported that as of the same year the total number of people in the U.S. who had tried the drug was 50 million. In the late 1980s, it was estimated that about 50 to 60 percent of people between the ages of 21 and 29 had tried marijuana at least once.

Marijuana and hashish are usually smoked, but may also be ingested orally,...