Cannabis, also known as marijuana among several other names, is a preparation of the Cannabis plant intended for use as a psychoactive drug or medicine. The main psychoactive part of cannabis is tetrahydrocannabinol (THC); one of 483 known compounds in the plant, including at least 65 other cannabinoids.

Marijuana—also called weed, herb, pot, grass, bud, ganja, Mary Jane, and a vast number of other slang terms—is a greenish-gray mixture of the dried, shredded leaves and flowers of Cannabis sativa, the hemp plant. Some people smoke marijuana in hand-rolled cigarettes called joints; many use pipes, water pipes (sometimes called bongs), or marijuana cigars called blunts (often made by slicing open cigars and replacing some or all of the tobacco with marijuana). Stronger forms of marijuana include sinsemilla (from specially tended female plants) and concentrated resins containing high doses of marijuana’s active ingredients, including honeylike hash oil, waxy budder, and hard amberlike shatter. These resins are increasingly popular among those who use them both recreationally and medically.

Marijuana is one of the most common used drugs.Its use is widespread among young people. In 2015, more than 11 million young adults ages 18 to 25 used marijuana in the past year. Rates of marijuana use among middle and high school students have dropped or levelled off in the past few years after several years of increase. However, the number of young people who believe marijuana use is risky is decreasing.