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Abstract
This thesis explored the effect of cocaine use on treatment outcomes for heroin dependent individuals in Sydney, Australia. A naturalistic, longitudinal design was employed in order to examine the effects of cocaine on outcomes over a two year period. Study 1 assessed the prevalence and correlates of cocaine use among heroin dependent individuals. Cocaine use was found to be common among entrants to all three of the major treatment modalities in NSW. Heroin users who also used cocaine (CU) displayed a poorer clinical profile at baseline than non-cocaine users (NCU), reporting higher levels of drug use and dependence, and a greater prevalence of needle risk-taking and criminal behaviour.
Study 2 examined outcomes three months post-study entry. CU and NCU were found to have been equally well retained in treatment. Despite significantly reduced levels of cocaine use amongst the cohort, however, CU continued to display the higher levels of drug-related harm that characterized them at baseline. In order to determine whether cocaine use itself was responsible for the greater levels of harm observed amongst CU, or whether instead CU were an inherently more dysfunctional group for whom cocaine use merely served as a marker, comparisons were made within groups on the basis of cocaine use patterns over the study period. The results of these analyses demonstrated that commencing cocaine use resulted in a clear decline in functioning, whereas cessation resulted in corresponding improvements.
In Study 3 outcomes were examined twelve months post-study. Baseline cocaine use was again found to predict poorer outcome, despite a large scale reduction in cocaine use amongst the cohort. Importantly, CU were significantly less likely than NCU to be abstinent from heroin at twelve months and more likely to have been incarcerated since study entry. In addition, the effect of persistence of cocaine use was examined. Results indicated that the harms associated with cocaine use increased with increasing persistence of use.
Outcomes at two years post-study entry were explored in Study 4. At this time CU and NCU recorded similar outcomes in most domains. Thus, it appeared that the harms caused by cocaine use may take a substantial period of time to diminish. Patterns of cocaine use and motivations for cessation and commencement were also examined. Responses suggested that cocaine use amongst the cohort was largely opportunistic, with participants ceasing use for a variety of reasons, including the financial and psychological problems caused by cocaine use. Past year prevalence of cocaine dependence was measured in this study, with the majority of those who had used cocaine in the past year meeting criteria for dependence.
In Study 5, generalized estimating equations were used to measure the effect of baseline cocaine use on major outcome variables over the entire two year study period. Even after controlling for treatment variables, heroin use and other baseline polydrug use, the results of this study confirmed previous findings within the thesis by demonstrating the negative effect of baseline cocaine use on most outcome variables.
Evidently, cocaine use among dependent heroin users has serious, long lasting, consequences. To date, however, there has been a stark lack of research examining the effect of cocaine use on treatment outcomes for heroin dependence. To that end, the results of this thesis are encouraging, suggesting that treatment for heroin dependence may also aid in reducing cocaine use among this group.