Background: Schizophrenia consistently ranks among the leading causes of disability worldwide, and is significantly overrepresented in socially disadvantaged populations. Despite demonstrated efficacy of antipsychotic medication in research studies, poor adherence limits its effectiveness in real-world practice. Remarkably, antipsychotic adherence has never been examined in homeless or justice-involved patient cohorts under naturalistic conditions, and current treatment guidelines provide little information on practices to improve outcomes in these important subgroups. The three original research studies that comprise this thesis address this substantial omission in existing literature. Methods: The studies include population-level analysis, retrospective cohort design and a randomized controlled trial. Offenders diagnosed with schizophrenia, prescribed antipsychotic medication and convicted under British Columbia jurisdiction were the basis for longitudinal epidemiological analysis. A homeless cohort of Vancouver patients with severe mental illness enabled retrospective analysis of antipsychotic use, and examination of changes in adherence following randomization to different supported-housing treatment conditions. All three analyses drew on a centralized administrative repository of comprehensive prescription details. Adherence was operationalized using the medication possession ratio (MPR). Results: Over an average follow-up of 10 years, findings from the offender sample (n=11,462) revealed a mean MPR of 0.41. Results further demonstrated that patients who met guideline-level adherence (MPR≥0.80) were significantly less likely to be convicted of both violent and non-violent offences. 15-year retrospective analyses of homeless patients also showed an average MPR of 0.41. Higher antipsychotic adherence was significantly associated with duration of homelessness, prescription of long-acting injectable medication and primary care engagement. Randomization to market housing with assertive community treatment resulted in near guideline-level adherence (0.78), while assignment to congregate supported-housing and treatment as usual led to relatively low levels of adherence (0.55 and 0.61, respectively). Conclusion: Results demonstrate that homeless and/or justice-involved patients with schizophrenia have very low levels of adherence to prescribed antipsychotic medication. Findings were corroborated using two separate samples, in the context of universal health care, where prescribed medication is provided at no cost to patients of limited means. Action is needed to implement measures including those detailed in this research that have demonstrated promise to improve adherence among highly vulnerable patient groups.
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Thesis advisor: Somers, Julian
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