Exploration of the Comorbidity of Cannabis Use Disorders and Mental Health Disorders among Inpatients Presenting to All Hospitals in New South Wales, Australia

Background: Cannabis is one of the most commonly used illegal psychoactive substances and its use often coexists with mental health disorders. Objectives: This study explores the relationships between cannabis use disorders and some common mental health disorders. Methods: Admissions to all New South Wales (NSW) hospitals were analyzed. The data were extracted from the NSW Department of Health Inpatient Statistics Data Collection for the period 1 July 2006 to 30 June 2007. Readmissions within 28 days were excluded. Data extraction and analyses were performed by using the SAS program. Chi-square tests and odds ratio were used to examine the association between cannabis use disorder and mental health disorders. Results: Of the 1.8 million admissions, associations between cannabis use disorders and mental health disorders were strong (odds ratio 7.8-10.7, p < .001). Inpatients (53.8%) who used cannabis had at least one identifiable mental disorder. Higher comorbidity rates were observed for females (39.6%) and for those aged between 30 and 49 years. Cannabis use disorder comorbid with the most common mental disorders were: anxiety disorder (3.4%), bipolar affective disorder (5.7%), major depressive disorder (10.9%), personality disorder (9.2%), schizophrenia (15.0%), and severe stress disorder (8.7%). Cannabis use disorder has strong associations with these mental health disorders (odds ratio 4.8-34.8). The average length of stay (ALOS) for cannabis use disorders was 9.0 days and the ALOS for the most common mental health disorders was 11.0 days. Conclusions and implications: This study provides detailed information about the association between cannabis use disorders and mental health disorders and extends our understanding of comorbidity presentations in inpatient admissions.