Clinical outcomes among patients with affective and non-affective psychosis and the role of substance use

Stewart, Bailey K. (2024) Clinical outcomes among patients with affective and non-affective psychosis and the role of substance use. Doctoral (PhD) thesis, Memorial University of Newfoundland.

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Abstract

Substance use is common among individuals experiencing psychosis and has important implications for clinical outcomes, symptomatic course, and treatment considerations. While research has largely focused efforts towards understanding the impact of cannabis in this population, insufficient attention has been paid towards alcohol in the existing literature. In addition, conclusions about the impact of substance use on patients with psychosis may be limited given that most research includes patients with affective and non-affective psychosis. There is some debate in the literature regarding the clinical utility of this dichotomy and further exploration is warranted. The aims of the current study were to: 1) examine the differences and similarities between patients with affective and non-affective psychosis; and 2) investigate whether substance use differentially impacts patients diagnosed with affective or non-affective psychosis. Patients were recruited from an early psychosis intervention program in St. John’s, NL and were diagnosed with either schizophrenia or bipolar disorder. Patients’ clinical characteristics (i.e., substance use, positive symptoms, overall functioning, illness severity, and overall improvement) were assessed at three time points: admission, 12 and 24 months. A significant interaction between diagnostic group and time was found and suggested that patients with schizophrenia tended to show greater levels of improvement over the course of 24 months compared to patients with bipolar disorder. Further, patients with schizophrenia who abused cannabis tended to improve over the same time while patients with bipolar disorder who abused cannabis tended to show a decline. The interaction between diagnostic group and time was not significant for positive symptoms, overall functioning, or illness severity. Patients with bipolar disorder were also rated as having higher overall levels of global functioning and lower levels of illness severity compared to patients with schizophrenia. Lastly, alcohol abuse was a significant predictor of various clinical outcomes, including overall functioning and illness severity. The current study highlights the clinical utility of the dichotomy between affective and non-affective psychosis, and the need to further examine the impact of substance use, particularly alcohol, in this population.

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