Impulsive traits and impulsive behaviour associated with opioid dependence : relationship to abstinence and heroin use

Opioid dependence is associated with significant morbidity and mortality. New and improved treatments are needed to foster improvements in abstinence rates. Heroin use is associated with impulsive traits and behaviour, and therefore addressing impulsivity within the context of opioid treatments may help to increase treatment efficacy. Impulsivity is a complex multifaceted construct, which has been defined and measured inconsistently. Additionally, studies examining impulsivity specifically in opioid dependence are scarce and usually recruit participants at the commencement of treatment, who may exhibit different behaviours from opioid-dependent individuals in the general community. No study has comprehensively assessed impulsivity in opioid-dependent individuals in a naturalistic setting to establish which facets of impulsivity may be targets for intervention. Therefore, the primary aim of this thesis was to determine the association between facets of impulsivity and ongoing heroin use in opioid-dependent individuals. This thesis reports on a study of 72 opioid-dependent individuals on opioid-substitution pharmacotherapy in the general community and 25 matched healthy controls. Participants in the study reported their drug use using standardised measures, and were administered a battery of measures that were based on a comprehensive framework of impulsivity. The impulsivity assessment included motor impulsivity tested using the Go/No-Go (GNG) Task, temporal impulsivity tested using the Monetary Choice Questionnaire (MCQ), reflection impulsivity tested using the Information Sampling Task (IST), and impulsive decision making assessed using the Iowa Gambling Task (IGT) and Cambridge Gambling Task (CGT). Participants also self-reported their impulsivity on a questionnaire, the Barratt Impulsiveness Scale (BIS). The findings of this thesis revealed that some facets of impulsivity, but not all, were associated with opioid dependence, relative to controls. We then followed the opioid-dependent participants longitudinally, and based on their heroin use patterns at baseline,1-month, 2-months, 3-months, and 6-months, we classified the opioid dependent participants into groups of heroin-use patterns using latent class growth analysis. Four classes emerged (abstinent, low use, high use, very high use), which we then compared on measures of impulsivity. Difference emerged between the abstinent and non-abstinent groups, but not between the low and high heroin-use groups. Mood was associated with self-reported but not performance-based behavioural measures of impulsivity and did not relate to frequency of heroin use. Novel aspects of the methodology in this thesis are the explicit use of a comprehensive framework of impulsivity, and the classification of participants based on robust statistical models of their heroin-use patterns. This research makes important contributions to understanding that multiple self-reported and performance-based behavioural measures of impulsivity appear to reflect distinct aspects of the construct of impulsivity. As such, a comprehensive assessment of impulsivity is needed to accurately reflect the complex relationship between aspects of impulsivity and opioid use. Such a comprehensive assessment of impulsivity may provide important indications of how to identify those at risk of relapse, and to more precisely target treatment. For example, treatments to improve skills underlying decision making and temporal impulsivity may improve outcomes for opioid dependent individuals, e.g., evaluating decisions based on previous experience, and increasing the salience of small rewards.