Marijuana refers to the dried leaves, flowers, stems, and seeds from the hemp plant Cannabis sativa, which contains the psychoactive (mind-altering) chemical delta-9-tetrahydrocannabinol (THC), as well as other related compounds. This plant material can also be concentrated in a resin called hashish or a sticky black liquid called hash oil.

Marijuana is the most common illicit drug used in the United States. After a period of decline in the last decade, its use has been increasing among young people since 2007, corresponding to a diminishing perception of the drug’s risks that may be associated with increased public debate over the drug’s legal status. Although the federal government considers marijuana a Schedule I substance (having no medicinal uses and high risk for abuse), two states have legalized marijuana for adult recreational use, and 21 states have passed laws allowing its use as a treatment for certain medical conditions (see “Is Marijuana Medicine?”, below).

How is Marijuana Used?

Marijuana is usually smoked in hand-rolled cigarettes (joints) or in pipes or water pipes (bongs). It is also smoked in blunts—cigars that have been emptied of tobacco and refilled with a mixture of marijuana and tobacco. Marijuana smoke has a pungent and distinctive, usually sweet-and-sour, odor. Marijuana can also be mixed in food or brewed as a tea.

illlustration of chemical structures showing how similar the natural brain chemical anandamide is to marijuana's THCTHC's chemical structure is similar to the brain chemical anandamide. Similarity in structure allows drugs to be recognized by the body and to alter normal brain communication
How Does Marijuana Affect the Brain?

When marijuana is smoked, THC rapidly passes from the lungs into the bloodstream, which carries the chemical to