Both cross-sectional and longitudinal studies have demonstrated that use of illicit drugs, like cocaine, is reliably preceded by use of other drugs, like nicotine and alcohol (Yamaguchi & Kandel, 1984; Kandel & Davies, 1991; Kandel et al., 1992; Kandel & Yamaguchi, 1993; Merrill et al., 1999). The Gateway Hypothesis of drug abuse posits that the use of some drugs (Gateway drugs) increases the risk of subsequent drug abuse. If so, identification of factors that predispose to Gateway drug use may lead to early identification of those at risk for other drug use.

Several hypotheses have focused on either personality characteristics or environmental circumstances in the use of drugs and the progression of drug use (Jessor et al., 1980; Donovan et al., 1985; Donovan & Jessor, 1985; Wood et al., 1995; Costa et al., 1989; Donovan & Jesser, 1983; Swadi, 1999). For example, sensation seeking traits have been hypothesized to predict the initial foray into experimentation with psychoactive drugs (Wills et al., 1994). Because of the relative ease of procurement of nicotine and alcohol, these drugs would be most likely to be the ones used first. Initial use of other, more difficult to obtain and illicit drugs may follow as a result of a continuing search for new sensations and exposure to environmental circumstances that are more amenable to obtaining of these drugs.