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The gateway drug theory (also called gateway theory, gateway hypothesis and gateway effect) states that use of less deleterious drugs precedes, and can lead to, future use of more dangerous hard drugs〔 or crime. It is often attributed to the earlier use of one of several licit substances, including tobacco or alcohol, as well as cannabis.〔 The reverse gateway theory posits that earlier regular cannabis use predicts later tobacco initiation and/or nicotine dependence in those who did not use tobacco before. ==Cannabis== The hypothesis is that the use of soft drugs like cannabis leads to the use of harder drugs via a sequence of stages.〔 This is based on the observation that many consumers who use cocaine or heroin have previously used cannabis, and most have used alcohol or tobacco; the hypothesis is that progression of drug use initiation continues from there to other drugs like cocaine or heroin. Some research supports that cannabis use predicts a significantly higher risk for subsequent use of "harder" illicit drugs, while other research does not.〔 Some research even has found alcohol represented the "gateway" drug, leading to the use of tobacco, marijuana, and other illicit substances. While some research shows that many hard drug users used cannabis or alcohol before moving on to the harder substances, other research shows that some serious drug abusers have not used alcohol or cannabis first.〔 The latter is evident in Japan, where the overwhelming majority of users of illicit drugs do not use cannabis first.〔 One study finds no evidence that medical marijuana laws lead to an increase in cocaine or heroin usage. The risk factor for using drugs in cannabis users may be higher because few people try hard drugs prior to trying cannabis, not because cannabis users increasingly try hard drugs such as certain substituted amphetamines (e.g., methamphetamine). For example, cannabis is typically available at a significantly earlier age than other illicit drugs. Jacob Sullum analyzed the "gateway" theory in a 2003 ''Reason'' magazine article, noting that the theory's "...durability is largely due to its ambiguity: Because it's rarely clear what people mean when they say that pot smoking leads to the use of "harder" drugs, the claim is difficult to disprove.": : "Notice that none of these interpretations involves a specific pharmacological effect of the sort drug warriors seem to have in mind when they suggest that pot smoking primes the brain for cocaine or heroin. As a National Academy of Sciences panel observed in a 1999 report, 'There is no evidence that marijuana serves as a stepping stone on the basis of its particular drug effect.' Last year the Canadian Senate's Special Committee on Illegal Drugs likewise concluded that 'cannabis itself is not a cause of other drug use. In this sense, we reject the gateway theory.'" (The National Institute on Drug Abuse ) have noted that while most cannabis users do not go on to use "harder" substances, reported data is consistent with the theory that cannabis is a gateway drug. However, they also suggest an alternative explanation. It may be that some individuals are more prone to using drugs and that these people are more likely to start with readily available substances such as cannabis, tobacco, and alcohol.〔(【引用サイトリンク】url=http://www.drugabuse.gov/publications/marijuana/marijuana-gateway-drug )〕 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「gateway drug theory」の詳細全文を読む スポンサード リンク
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