Most of what we know about the effectiveness of prevention comes from studies of “universal” programs, which target the general population. These universal approaches, which often focus on incipient or “gateway” drug use, are based on the assumption that early experimentation with tobacco, alcohol, and marijuana can lead to more frequent use of these substances and progression into the use of other more dangerous substances. This gateway notion is rooted in early conceptions of marijuana as a stepping-stone to more serious drug involvement (Wagner and Anthony, 1999) as well as research evidence of a statistical link between age at first use of drugs and later more frequent or problematic use (Brunswick and Boyle, 1979; O’Donnell and Clayton, 1979; Robins and Przybeck, 1985; Anthony and Petronis, 1991)
Findings such as these and subsequent analyses of sequences of drug use patterns over time led to a developmental stage theory of adolescent involvement in legal and illegal drugs (Kandel, 1975; Kandel and Faust, 1975). According to this perspective, use of alcohol and tobacco precedes the use of illegal drugs, and the use of marijuana precedes the use of other illegal drugs. Early descriptions of this developmental process (e.g., Kandel, 1982) were careful to point out that most individuals who reach a given stage of substance use discontinue it for one reason or another, and that only a small subgroup of users at earlier stages actually progress to the next stage of use.
Although sophisticated research demonstrated that the use of legal drugs is associated with increased probability of marijuana use, and the use of marijuana is associated with increased probability of other illegal drug use (Yamaguchi and Kandel, 1984), the authors stress the limitations on the inferences about the link between use of one drug and use of another. They point out (p. 679) that personality and lifestyle variables, as well as environmental factors such as availability and supply, also explain the transition from one drug to another and from one level of use to another. In particular, they pointed out the need to control for individual propensity variables prior to the time of initiation into legal drug use. These effects due to heterogeneity in population characteristics are confounded with the early use of gateway substances.
The models do not rule out the alternative interpretation that some individuals are more likely to use more drugs, to use more dangerous drugs, to persist in their use for a longer period of time, and to begin their use earlier than others. This idea is consistent with the well-established findings in the criminological literature (Moffitt, 1993) that the offending