A New Trick for an Old Dog: Applying Developmental Trajectories to Inform Drug Use Progression

Summary

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The frequent criticisms of the "gateway hypothesis" have led scholars to note the importance of considering the role of intra-individual change for drug use progression. While studies employing drug use trajectories have added considerably to our understanding of drug use comorbidity, the extent to which trajectories inform drug use progression remains largely unknown despite the fact that there are several theoretical reasons to suspect that intra-individual change is important to the gateway phenomenon. The current study employs latent class growth models using a sample from the Boys Town study of adolescent drug and drinking behavior. The results demonstrate that knowing how gateway drug use changes over time provides important information above and beyond knowing frequency of gateway use for predicting harder drug use trajectories. Implications of the empirical findings and directions for future research are discussed.

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A New Trick for an Old Dog: Applying Developmental Trajectories to Inform Drug Use Progression

INTRODUCTION

One of the most contentious debates in the field of drug use and abuse is whether the use of one substance precedes and functions as a "gateway" to use of another harder drug. The gateway hypothesis posits that the typical sequence of substance use begins with alcohol or tobacco, moves into use of marijuana, and ends with harder drug use such as cocaine and heroin (Kandel, 1975; 2002; Kandel & Yamaguchi, 1999, Peele & Brodsky, 1997). While the gateway sequence has been supported across a variety of domestic and international samples (Kandel, Yamaguchi, & Chen, 1 992), it remains controversial for various reasons (Golub & Johnson, 1 998).

First, some researchers have challenged the order of the gateway sequence (Kandel, 2002), pointing out that not every individual who engages in drug use follows the same sequencing pattern (Andrews, Hops, Ary, Lichtenstein, & Tildesley, 1991; Blaze-Temple, & Lo, 1992). For instance, not only can entire stages of drug use be skipped (Golub & Johnson, 1 994) but drug use can often occur in the opposite direction of the expected gateway sequence (Blaze-Temple & Lo, 1992; Golub & Johnson, 1994; Mackesy-Amiti, Fendrich, & Goldstein, 1997; Young et al., 1995). Second, determining which substances should be categorized as gateway drugs is problematic and is frequently disputed (Kandel, 2002). Though many consider licit substances to be gateway drugs (Kandel et al., 1992; Kandel, 2002), marijuana is also frequently labeled a gateway drug to use of heroin, barbiturates, or other harder drugs (DeSimone, 1998; Golub & Johnson, 1994). Inconsistencies surrounding the sequencing of drug use have led some to question the focus of drug use progression research; for instance, Kandel (2002) asks "should one not refer to 'gateway use' of a drug rather than to a 'gateway drug'?" (p. 8). This shifts the emphasis of drug use progression research from strict sequencing to use patterns of a substance, drawing specific attention to the ramifications gateway use trajectories have for use trajectories of subsequent substances.

Despite the large number of dimensions that are employed to describe use of a drug (e.g., see Wohlwill, 1973), sequencing, age of onset, and frequency of use have received most of the empirical attention in drug use progression research (Fergusson & Horwood, 2000; Labouvie & White, 2002). Initiation of alcohol use at an...

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