Substance abuse and quality of life among severely mentally ill consumers: a longitudinal modelling analysis.

BACKGROUND: Evidence suggests that substance abuse negatively affects both psychiatric symptom severity and quality of life (QOL) in people with severe mental illness (SMI). However, these relationships have not been examined simultaneously, nor have they been characterized over time. Thus, it is difficult to appreciate the extent to which substance abuse exerts an enduring effect on psychiatric symptoms and distress and/or QOL in this population. The purpose of this study is to test a conceptual model linking these factors together.
METHODS: Subjects were participants in a longitudinal evaluation of community mental healthcare in Ontario (n = 133). Comprehensive consumer assessments were conducted at treatment entry, and at 9 and 18 months. Subjects were receiving intensive case management or assertive community treatment throughout the 18-month study period. Structural equation modelling was used to examine the concurrent and longitudinal relationships between substance abuse, symptoms and distress, and QOL.
RESULTS: The prevalence of substance abuse was 55.0%. The SEM analysis suggested that substance abuse at baseline was associated with elevated symptomatology and distress and lower QOL, and that these effects endured after 18 months of treatment. Psychiatric symptoms and distress mediated the negative relationship between substance abuse and QOL.
CONCLUSIONS: The mediating role played by symptom and distress levels in the relationship between substance abuse and QOL suggests the importance of closely monitoring changes in these factors among SMI patients with substance problems. Tracking symptom severity and distress levels over time will allow service providers to intervene and potentially improve the QOL of individuals with SMI.