Letter From the Director

Image of a marijuana plant What is Marijuana? Marijuana—often called pot, grass, reefer, weed, herb, Mary Jane, or MJ—is a greenish-gray mixture of the dried, shredded leaves, stems, seeds, and flowers of Cannabis sativa—the hemp plant.

By the time they graduate from high school, about 46 percent of teens will have tried marijuana.1 Although current use among U.S. teens has dropped dramatically in the past decade (to a prevalence of about 15 percent in 2011), this decline has stalled during the past several years.2 These data are from the Monitoring the Future survey, which has been tracking drug use among teens since 1975. Still, the World Health Organization ranks the United States first among 17 European and North American countries for prevalence of marijuana use. And more users start every day. In 2010, an estimated 2.4 million Americans used marijuana for the first time; greater than one-half were under age 18.1

The use of marijuana can produce adverse physical, mental, emotional, and behavioral effects. It can impair short-term memory and judgment and distort perception. Because marijuana affects brain systems that are still maturing through young adulthood, its use by teens may have a negative effect on their development. And contrary to popular belief, it can be addictive.

We hope that this Research Report will help make readers aware of our current knowledge of marijuana abuse and its harmful effects.

Nora D. Volkow, M.D.
National Institute on Drug Abuse

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This page was last updated July 2012