the gateway drug theory (also called gateway theory, gateway hypothesis and gateway effect) states that the use of less deleterious drugs can lead to a future risk of using 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 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 
Substance_dependence Theories