Background: Impairments in cognition are considered as one of the core features of psychotic disorders, including impairments in executive functioning (EF). EF is an umbrella term that incorporates...Show moreBackground: Impairments in cognition are considered as one of the core features of psychotic disorders, including impairments in executive functioning (EF). EF is an umbrella term that incorporates several higher cognitive functions. Findings on the relationship between substance use and EF are inconsistent. A potential mechanism underlying the effect of substance use on EF may be sleep disturbance. Therefore, the aim of this thesis study was to identify the relationship between substance use and EF in people diagnosed with a psychotic disorder and examine whether sleep quality mediates this relationship. Methods: The current sample comprised 301 participants with a primary diagnosis of a psychotic disorder. Schizophrenia was the most common diagnosis in the sample (43.2%). EF was assessed using the Behaviour Rating Inventory of Executive Function for Adults (BRIEF-A). Substance use was assessed using the Measurements in the Addictions for Triage and Evaluation questionnaire (MATE). Sleep quality was assessed using the Pittsburgh Sleep Quality Index (PSQI). Results: Results of a linear regression analysis showed a significant positive relationship between the MATE and BRIEF-A (β = .25, p < .001). The mediation analysis confirmed this significant positive relationship between the MATE and the BRIEF, by a significant total effect (β = .25, p = .001). The indirect effect of the MATE on the PSQI was not significant (β = -.0004, p = .996). The indirect effect of the PSQI on the BRIEF-A was significant (β = .22, p = .002). The direct effect of the MATE on the BRIEF-A was significant as well (β = .25, p < .001). Conclusion: Our findings suggest that more problematic substance use is associated with worse EF. This relationship is not mediated by sleep quality in our study, as substance use was not found to be associated with sleep quality. However, we found that better sleep quality was associated with better EF. These results highlight the importance of taking substance use and poorer sleep quality into account in the treatment of psychotic disorders.Show less
