Research on cravings has focused on nicotine, alcohol, cocaine, and opiate drugs. It has not specifically addressed marijuana, so it remains unknown whether marijuana induces similar changes in brain function.

MARIJUANA USE AND DEPENDENCE

Another way to look at the risk of marijuana addiction is to examine general patterns of use and dependence. Who uses marijuana? How frequently and under what circumstances do marijuana users become abusers? How do patterns of marijuana abuse compare with those of other abused substances? Social scientists and epidemiologists have addressed several aspects of these questions in recent years.

Millions of Americans have tried marijuana, but most do not use it regularly. According to a U.S. Department of Health and Human Services household survey conducted in 1997, 33 percent of the U.S. population over the age of 12 (some 70 million people) has tried marijuana or hashish at least once. Only 5 percent of respondents reported that they currently use either substance. Marijuana use was most prevalent among people between 18 and 25 and declined sharply in people age 34 and older.

These results fit a long-observed scenario: many people try marijuana as adolescents, but few continue to use it past young adulthood (see Figure 3.1). Peer pressure, as well as the desire to conform or appear mature, typically prompts teenagers to try marijuana for the first time. Different factors, however, appear to influence marijuana use beyond mere experimentation.

In one study of 456 students who tried marijuana while in high school, those who became regular (but not heavy) marijuana users typically said they continued to take the drug to improve their mood, rather than for any social reason.20 This finding is in keeping with additional research on young adults, who tend to use drugs on a regular basis to satisfy psychological needs rather than to impress others.

Only 28 percent of the high school students continued using marijuana after their initial experimentation with the drug. Several who quit did so because they felt that marijuana had harmed either their health or their relationships with other people. Some



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