Trajectories of heroin use: 10-11-year findings from the Australian Treatment Outcome Study
The Australian Treatment Outcome Study (ATOS) is a landmark study of the pathways of heroin use and one of the few to be conducted outside of the US. The purpose of the 10 year follow up of the original 615 participants was to identify pathways of heroin use in Australia, predictors of trajectory group membership and subsequent outcomes among people with heroin dependence over 10–11 years.
A total of 615 participants were recruited between 2001 and 2002 as part of the Australian Treatment Outcome Study (66.2% male; mean age 29 years). This analysis focused on 428 participants for whom data on heroin use was available over 10–11 years following study entry.
Six trajectory groups were identified out of the 428 identified for this study. One in five (22.1%) were classified as having ‘no decrease‘ in heroin use, with the probability of using remaining high during the 10–11 years. One in six were classified as demonstrating a ‘rapid decrease to maintained abstinence’. The probability of heroin use among this group declined steeply in the first 2–3 years and continued to be low. The remaining trajectories represented other fluctuating patterns of use. Few baseline variables were found to predict trajectory group membership, but group membership was predictive of demographic, substance use and physical and mental health outcomes at 10–11 years.
Conclusion and Discussion
Long-term trajectories of heroin use in Australia appear to show considerable diversity. During a decade of follow-up, with few risk factors predicting group membership, just over a fifth continued to use at high levels, while fewer than a fifth become abstinent early on and remained abstinent. The remainder showed fluctuating patterns.
Despite methodological differences, there was some consistency between the groups identified in this study and those identified by previous research. All studies have identified a group in which use remains high across time. Twenty-two per cent of the ATOS cohort demonstrated ‘no decrease’ in the probability of heroin use during the 10–11-year period (> 0.98) emphasizing that, for some, heroin dependence is a chronic, debilitating disorder requiring a long-term response. At the other end of the spectrum, one in six participants demonstrated ‘rapid decrease with maintained abstinence’. It is important to note that although these reductions appeared within the first 2–3 years of follow-up, on average, participants in the ATOS cohort had already been using heroin for 10 years at study entry. Pathways in between the ‘no decrease’ and ‘rapid decrease to maintained abstinence’ were more variable, reflecting patterns of rapid and gradual reductions in the probability of use followed by periods of early and late relapse over time.
For some, heroin dependence is a chronic, debilitating disorder requiring early intervention and a long-term response. There were, however, few characteristics found to predict which path a person might take. In particular, there was little to differentiate those who would continue to use and those who would achieve maintained abstinence. Further research is needed to improve our understanding of factors that underlie group membership and the role of dynamic factors that may influence trajectories.