Objectives: Co-morbidity with cannabis use disorder is common in patients with a psychotic disorder and is associated with adverse outcome. This study aimed to determine prevalence of cannabis use disorder among patients with a psychotic disorder and subjects at ultra high risk of psychosis and to study the influence of cannabis use on severity of (pre-)psychotic symptomatology, psychosocial functioning and variables related to the course of the disorder in these patients.
Methods: In this study 169 consecutively assessed patients with a psychotic disorder were included as well as 59 consecutively assessed subjects at ultra high risk of psychosis.
Results: 45% of the patients with a psychotic disorder and 27% of the UHR patients were diagnosed with a co-morbid cannabis use disorder. Patients with cannabis use disorders did not differ from patients without cannabis use disorder in severity of psychotic symptoms. However, excluding patients with substance use disorder other than cannabis use disorder resulted in higher scores on positive symptom levels for patients with cannabis use disorder compared to patients without any substance use disorder. Regarding ultra high risk patients, subjects with cannabis use disorder did not differ from subjects without cannabis use disorder on severity of pre-psychotic symptomatology. However, a negative correlation was found between the amount of cannabis used recently and scores on the pre-psychotic negative subscale.
Conclusion: Our results suggest a specific association between cannabis abuse and psychotic symptomatology.