by the Institute of Medicine

About the author: The Institute of Medicine (IOM), associated with the National Academy of Sciences, is a private organization that aims to improve health and science policies on the federal, public, and private levels.

Millions of Americans have tried marijuana, but most are not regular users. In 1996, 68.6 million people—32% of the U.S. population over 12 years old—had tried marijuana or hashish at least once in their lifetime, but only 5% were current users. Marijuana use is most prevalent among 18- to 25-year-olds and declines sharply after the age of 34. Whites are more likely than blacks to use marijuana in adolescence, although the difference decreases by adulthood.

Most people who have used marijuana did so first during adolescence. Social influences, such as peer pressure and prevalence of use by peers, are...