however, most future drug users become well acquainted with alcohol and nicotine—usually when they are too young to do so legally.

Discussions of marijuana as a gateway drug usually refer to—and often confuse—two distinct behavioral scenarios. The first, more often called the “stepping stone” hypothesis, is the notion that marijuana possesses pharmacological properties that compel users to experiment with harder drugs. The second and more common theory is that marijuana opens a door to the world of illegal substances. Once introduced to illicit drug use via marijuana, young people encounter increased peer pressure to try other drugs and gain easier access to them.

The stepping-stone hypothesis applies to marijuana only in the sense that individuals who enjoy marijuana's effects probably have a stronger than average attraction to mood-altering substances. In other words, many of the same factors that induce people to use marijuana are likely to predispose them to use harder drugs as well. Those factors include physiological reactions to drugs, the psychological state of the user, and the social context in which the drug is used. Additional factors are addressed by the gateway theory, which asserts that marijuana, due to its illegal status, serves as a conduit to harder drugs.

People who are most likely to use illicit drugs other than marijuana tend to share several traits, including use of alcohol or nicotine at an early age, heavy marijuana use, and psychiatric disorders. Yet while it appears that people who try alcohol and nicotine earliest are more likely than others to experiment with illegal drugs, they are no more likely to become heavy drug users. Similarly, experimental or infrequent users of marijuana are less likely to progress to harder drug use than those who smoke marijuana on a daily basis. One study of young adult males found that those who had used marijuana between 10 and 99 times in their lives were unlikely to have tried another illicit drug, while more than half of those who had used marijuana more than 100 times had done so.32

Data that have been collected on the gateway phenomenon are frequently overinterpreted. For example, in one study, researchers concluded that “marijuana's role as a gateway drug appears to have increased” based on interviews with drug abusers

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