Prevalence of comorbid bipolar and substance use disorders in clinical settings, 1990–2015: Systematic review and meta-analysis

Background Comorbidity between substance use disorders (SUDs) and bipolar disorder (BD) is highly prevalent to the extent it may almost be regarded the norm. This systematic review and meta-analysis aimed to estimate the prevalence rates of SUDs in treatment seeking patients diagnosed with BD in both inpatient and outpatient settings. Methods A comprehensive literature search of Medline, EMBASE, psychINFO and CINAHL databases was conducted from 1990 to 2015. Prevalence of co-morbid SUDs and BD were extracted and odds ratios (ORs) were calculated using random effects meta-analysis. Results There were 151 articles identified by electronic searches that yielded 22 large, multi-site studies and 56 individual studies describing comorbid rates of SUDs amongst community dwelling, BD inpatients or outpatients. The SUDs with the highest prevalence in BD were alcohol use (42%) followed by cannabis use (20%) and other illicit drug use (17%). Meta-analysis showed males had higher lifetime risks of SUDs compared to females. BD and comorbid SUDS were associated with earlier age of onset and slightly more hospitalisations than non-users. Limitations The results do not take into account the possibility that individuals may have more than one comorbid disorder, such as having more than one SUD, anxiety disorder, or other combination. Some of the meta-analyses were based on relatively few studies with high rates of heterogeneity. Most included studies were cross-sectional and therefore causality cannot be inferred. Conclusions This systematic review shows comorbidity between SUDs and bipolar illness is highly prevalent in hospital and community-based samples. The prevalence of SUDs was similar in patients with bipolar I and bipolar II disorders. This study adds to the literature demonstrating that SUDs are common in BD and reinforces the need to provide better interventions and properly conducted treatment trials to reduce the burden conferred by comorbid SUD and BD.