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Reasons for Substance Use in Psychosis

Gregg, Lynsey

[Thesis]. Manchester, UK: The University of Manchester; 2011.

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Abstract

Large numbers of people with a diagnosis of psychosis use drugs and alcohol, resulting in poorer symptomatic and functional outcomes for many. A better understanding of the causes of this increased comorbidity is necessary if treatments designed to help people with psychosis abstain from or reduce their substance use are to be successful. The aim of this programme of research was to examine reasons for substance use in people with psychosis; to develop a new self report questionnaire of reasons for substance use and to use the new measure to test a multiple risk factor model of substance use maintenance. The psychometric properties of the new Reasons for Substance use in Schizophrenia (ReSUS) questionnaire were investigated in a clinical sample (n = 230) and the relationship of the different ReSUS subscales to psychopathology, coping strategies and substance use were examined in a series of studies. Coping reasons for use were less frequently endorsed than social and individual enhancement reasons but were related to psychopathology and to problematic substance use in both clinical and non-clinical samples. Coping reasons, enhancement reasons and dysfunctional coping strategies partially mediated the relationship between psychopathology and problematic substance use in a non-clinical sample (n = 221). Distress in relation to symptoms and coping reasons for use mediated the relationship between symptoms and substance use consequences in a clinical sample (n = 82) indicating that some substance use may be considered an attempt to self medicate psychiatric symptoms. An experience sampling study of cannabis use in daily life (n = 42) investigated the temporal relationship between symptoms and cannabis use and found that affect but not positive symptoms predicted cannabis use for a subgroup of people who reported using cannabis to cope: for these individuals cannabis use was more likely when positive affect was reduced and when negative affect was increased. The studies in this thesis have methodological limitations that will need to be addressed through future research. However, they extend the current literature on substance use in psychosis and lend credence to a cognitive motivational perspective on substance use. Results highlight the role of coping reasons for use in predicting substance use outcome and suggest that future research and clinical work in psychosis and substance use comorbidity should take self reported reasons for use into account.