Substance use pathways to methamphetamine use among treated users

Abstract

Considerable research has focused on patterns of substance use initiation among adolescents and for users of selected drugs; however, few data are available for methamphetamine (MA) users. This study describes substance initiation patterns for 352 MA users and assesses predictors of age of MA initiation and its sequencing. Subjects were randomly selected from treatment admissions in a large California county and interviewed using an extensive natural history protocol. Average age of MA initiation was 19 years. Nearly all (95%) had used alcohol, marijuana, and tobacco (average initiation age 13); inhalants, hallucinogens, and crack were also commonly used earlier in the drug sequence than MA. Earlier age of MA initiation was related to race/ethnicity (being non-African–American), younger age of first use of any substance, more types of early criminal behavior, and initiating MA use for sensation-seeking reasons. Following initiation of alcohol, marijuana, and/or tobacco, 27% initiated MA before other illicit drugs, 18% initiated another illicit drug before MA, and 56% initiated two or more other illicit drugs before MA. Later MA order in the initiation sequence was related to ethnicity (being African–American) and initiating MA to substitute for another drug. Results may support targeted prevention efforts and development of more effective interventions.

Introduction

Research on the patterns and sequence of drug initiation is accruing and has the potential to better inform the development of prevention and early intervention strategies. Much of this research has been directed to three broad areas: the adolescent period, which typically encompasses initial onset of drug use, substances used earliest in the sequence, and general populations, most of whom do not progress to serious use of drugs. Some studies have focused on problem populations of serious drug users, with a majority of this limited research focusing on opiate and cocaine use. Little is known about the patterns of drug use development specifically for users of methamphetamine (MA), a drug now labeled a principal drug threat because of epidemic increases in its use during the past decade. While problems associated with MA abuse have been recognized for many years, MA has now become the focus of national strategies for combating its spread and impact (Drug Enforcement Administration, 2005, National Drug Intelligence Center, 2004, Office of National Drug Control Policy, 2000, Office of National Drug Control Policy, 2005, Pennell et al., 1999). Examination of patterns of drug initiation among MA users can better inform these efforts.

Considerable research exists on patterns of onset of substance use among adolescents, with results showing typical progression through initiation of alcohol, tobacco, and marijuana before use of other illicit drugs (e.g. Ellickson et al., 1992, Kandel & Yamaguchi, 1993, Newcomb, 1995, Oetting & Beauvais, 1990, Young et al., 2002, Yu & Williford, 1992). In general populations, earlier age of onset of alcohol use has been found to be predictive of later problem use of alcohol and of use of illicit drugs (e.g. Fergusson, Lynskey et al., 1994, Grant & Dawson, 1998, Gruber et al., 1996, Hawkins et al., 1997, Kandel & Yamaguchi, 1993). While use of marijuana has often been found to be a precursor of other illicit drug use and early marijuana use is associated with increased risks of progression to other illicit drug use and abuse (Fergusson & Horwood, 2000, Lynskey et al., 2003), other studies have found that marijuana use was not a necessary precondition for progression to other illicit drug use (Blaze-Temple & Lo, 1992). By contrast, among native American youth who had used two or more drugs, marijuana was more likely to be initiated before alcohol (Novins, Beals, & Mitchell, 2001).

Patterns of substance use onset are less consistent for specific populations that have progressed to regular use of illicit drugs. For example, in a study of intravenous heroin users, results supported the common pattern of earliest onset of alcohol and tobacco (average age 13.4 and 13.6, respectively) followed by marijuana (age 14.8). In that sample, heroin was initiated at an average age of 18.8 years, a year earlier than MA for the 46% who had used MA (Zinkernagel et al., 2001). However, other studies have found that marijuana was the initial drug used by a large proportion of regular drug users and also that many initiated use of other illicit drugs prior to either alcohol or marijuana (Golub & Johnson, 1994, Mackesy-Amiti et al., 1997).

Describing drug progression and selected personal and contextual conditions that are related to this progression may facilitate the identification of risk factors and critical periods for developing interventions to delay onset or progression. Regrettably, we know little about such patterns of drug use initiation among the increasing numbers of MA users.

This paper describes substance/drug initiation patterns, including age of initiation and sequence of substances used, for methamphetamine (MA) users sampled from admissions to substance abuse treatment programs in Los Angeles County. In addition, we consider the relationships of selected user characteristics to age of MA initiation and to the relative order of MA initiation within the drug initiation sequence.