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Abstract
Violent offending and injecting drug use (IDU) are highly comorbid, serious behaviours. Despite extensive empirical investigation, the mechanisms underpinning this comorbidity remain unclear, which is, in part, due to a widespread assumption that drug use causes violence. In an effort to better understand the liability to violent offending among IDU, this thesis aimed to answer three major unresolved issues: (i) Does drug use cause violence or do underlying factors predispose individuals to drug use and violence? (ii) Is there heterogeneity in the nature of, and risk profiles for, violent offending? (iii) Are risks for violent offending specific to IDU?
Addressing these issues was possible through quantitative examination of two large epidemiological datasets: one of community-based IDU (N=300) and a large treatment-based case-control sample (N=1,927). Analyses were structured according to a developmental framework that has not previously been used in this area. This framework focuses on the impact of early life predisposing factors on long term adverse behavioural outcomes. Violent offending was found to be highly prevalent among IDU, with a significant minority (approximately one-third) having committed a serious, injurious violent act. Findings regarding the risks for the likelihood (Chapter Two), severity (Chapter Three), stability (Chapter Four) and specificity (Chapter Five) of violent offending were remarkably consistent across the Chapters. Childhood psychopathology, higher scores on aggressive and impulsive trait measures, and childhood maltreatment were found to be strongly, positively correlated with the initial liability to violent offending. Substance use, on the other hand, appeared to play a greater role in the maintenance of violent behaviour. The findings further indicated that heterogeneity in violent patterns was best explained by the extent of cumulative exposure to early-life and substance use risks, such that IDU with greater early-life risk exposure engaged in more stable, serious violent behaviour. The antisocial markers noted among violent IDU were absent in a matched Control group, supporting a hypothesis of risk specificity for violence.
This thesis provides new information to a growing literature regarding the substance use-violent offending association, and has implications for the early identification and intervention in individuals at high risk for an adverse developmental course