Gateway Drugs Theory

Initiation of substance use usually occurs in nonrandom but trivial temporal order. Unsurprisingly, the use of any substances is preceded by nonuse, and the first use of illicit drugs is usually preceded by consumption of licit substances. The use of "hard" drugs, such as cocaine and heroin, is usually preceded by "soft" drugs, such as marijuana. The sequential order becomes even less consistent beyond the initiation of involvement with illicit compounds, to the degree that the illicit drugs other than marijuana, that is, hard drugs, are usually collapsed in one class in research modeling use sequences. Moreover, a substantial proportion of drug users initiate their drug involvement with illicit rather than licit drugs, or use hard drugs before marijuana.