Personality and drugs of choice

Abstract

Although drug preference has been studied from the perspectives of individual differences and comorbid psychopathology, research incorporating both of these levels of analysis has been limited. In the current study, inpatients in a substance abuse treatment facility who reported preferences for alcohol, marijuana, methamphetamines, cocaine, heroin, or crack cocaine were compared in terms of their scores on measures of higher-order personality variables and psychopathology constructs representing lower-order elements of these factors. Results suggested that a broad externalizing dimension differentiated heroin users from alcohol, marijuana, and cocaine users. With the single exception that crack users remained more paranoid than alcohol users, psychopathology variables did not provide more specific discriminatory ability after broad personality factors were controlled. Implications for substance use research are discussed, with a focus on the utility of integrating individual differences and psychopathology constructs.

Introduction

Recent research has identified two broad personality dimensions that capture much of the relations between and represent heritable risk factors for psychiatric disorders including substance use (e.g., Achenbach, 1966, Krueger, 1999, Krueger et al., 2001, Krueger et al., 2002, Wolf et al., 1988). Internalizing relates to generalized psychological distress, is generally the first factor extracted from multi-scale measures of psychopathology, and tends to be sensitive to a wide range of problems in living. Externalizing is often more directly associated with behaviors that cause distress for others and (to a lesser extent or as a consequence) self, including substance use disorders. These integrative dimensions bear clear resemblance to broad dimensional models of personality (e.g., Eysenck, 1998, McCrae and Costa, 2003; see Markon, Krueger, & Watson, 2005).

Personality traits related to the internalizing and externalizing factors have been found to predict the type of substance likely to be used. For example, LeBon et al. (2004) showed that heroin addicts had higher levels of novelty seeking (a trait that is empirically related to externalizing; Markon et al., 2005), than alcoholics or controls, and that both heroin and alcohol users had higher levels of harm avoidance (related to internalizing; Markon et al., 2005) than controls, but were not different from one another. Conway, Swendsen, Rounsaville, and Merikangas (2002) found that constraint, a trait (negatively) related to externalizing (Markon et al., 2005), distinguished opioid and cocaine (lower constraint) from marijuana and alcohol (higher constraint) users.

Psychopathology constructs such as mood disorders are widely considered risk factors for substance abuse, and it is typically recommended that substance use must be stabilized before other disorders are treated. Whatever the clinical merits of these practices, they rest on the assumption that substance use and other forms of psychopathology represent discrete and quasi-independent constructs, and may not fully take their shared individual difference factors into account. Similarly, research demonstrating that psychopathology varies among individuals with different drugs of choice, such as a study by Donovan, Soldz, Kelley, and Penk (1998) indicating that heroin users were more depressed than alcohol and cocaine users and cocaine users were more manic than alcohol and heroin users, have tended not to take broader individual differences into account.

A better understanding of the influence of both broad personality dimensions and narrower symptom domains on drug choice would be useful for research on personality–behavior relations and would facilitate clinical assessment in substance using populations. For example, such research would enable a clearer understanding of personality as an etiological factor in substance use, as well as the influences of substances on personality. A clearer understanding may also improve predictions about likely correlates and risk factors for substance use. In addition, interventions may be targeted to treat underlying predispositions, thus ameliorating both psychopathological syndromes and the risk for substance use. Furthermore, it would provide a parsimonious explanation for the many “comorbidities” commonly observed between psychopathology and substance use.

Several possibilities exist with regards to the relations between personality, psychopathology and substance preference. Drugs of choice, given a temperamental predisposition to use, may be a function of factors not captured by personality dimensions (Krueger et al., 2001). Such factors might include psychopathology constructs, given that several studies using multi-scale self-report instruments have found that narrower trait/psychopathology constructs appear to differentiate substance users from non-users (e.g., Hopwood et al., 2007, Ruiz et al., 2003) and types of users from one another (e.g., Conway et al., 2002, Donovan et al., 1998, LeBon et al., 2004). Other potential factors that could influence substance of choice may include social influence, cultural mores, local availability of substances, demographic variables, or preferences related to personal conditioning histories.

Conversely, personality dimensions may relate to both a propensity to engage in substance use and a relative propensity to use different kinds of substances. For example, individuals with moderate levels of internalizing and externalizing characteristics may use substances associated with less severe impact on functioning, or perhaps with greater social acceptability (e.g., alcohol, marijuana), whereas, individuals with extremely high levels of these factors may use a variety of substances, including drugs that can have more serious short- and long-term impact on functioning and are less socially acceptable (e.g., cocaine, heroin). Trait dimensions may also differentially predict substance preference. For example, individuals with a high level of internalizing may prefer drugs with anxiolytic properties whereas individuals with a high level of externalizing may prefer drugs with disinhibiting properties.

The current study was designed to investigate the influence of both broad personality domains and narrower syndromal constructs on drugs of choice by testing three hypotheses. First, based on previous literature, it was anticipated that substance users would have elevated levels of internalizing and externalizing symptoms relative to a community population. Second, the hypothesis that these factors would also differentiate groups of individuals defined by their substance of choice was tested. Third, lower-order psychopathology constructs related to internalizing and externalizing were tested for their ability to differentiate groups defined by substance of choice, after accounting for broader personality factors.