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

Abstract

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.