Bipolar disorder and co-occurring cannabis use disorders: Characteristics, co-morbidities and clinical correlates
Highlights
► We examine rates of co-morbid mental disorders and indicators of the course of illness among individuals with bipolar disorder and cannabis use disorders (CUD). ► Among individuals with bipolar disorder, concurrent CUD were associated with increased risk for nicotine, alcohol and drug use disorders. ► Among individuals with bipolar disorder, concurrent CUD were associated with earlier age of onset and greater annual number of bipolar episodes. ► Co-occurring CUD are associated with significant co-morbidities and a more severe course of illness among individuals with bipolar disorder.
Introduction
Bipolar I and II disorders are serious mental illnesses that have been reported to occur in approximately 1–3% (Narrow et al., 2002, Grant et al., 2005) and 3–5% (Berk and Dodd, 2005, Cerullo and Strakowski, 2007) of the population, respectively. They are, globally, the sixth leading cause of disability (Woods, 2000). Bipolar disorders are often complicated by co-occurring substance use disorders, which are associated with increased co-morbidities (Gao et al., 2008). Cannabis is the most common illicit substance used among individuals with bipolar disorder (Cerullo and Strakowski, 2007) and up to 38% of individuals with bipolar disorder misuse cannabis (Etain et al., 2012). Cannabis abuse has particularly been reported to be high among young bipolar patients (Dell'Osso et al., 2011), and chronic cannabis use is associated with higher severity of illness and greater treatment non-compliance among individuals with bipolar disorder (van Rossum et al., 2009).
Despite numerous reports on co-occurrence between bipolar disorder and substance use disorders (see for example review by Cerullo and Strakowski (2007)), few studies have focused particularly on the relationship between CUD and bipolar disorder. In a longitudinal study by Strakowski et al. (2007), co-occurring CUD was found to be associated with more overall time in affective episodes and with more rapid cycling. Baethge et al. (2005) reported that in a prospective study on a clinical sample of bipolar patients, cannabis dependence was particularly associated with more manic episodes. Agrawal et al. (2011) reported results from a case-control study showing that co-occurring CUD was associated with increased suicide attempts, mixed episodes and disability.
Nevertheless, data pertaining to characteristics and co-occurrence of cannabis use disorders (CUD) among individuals with bipolar disorder are still scarce. The aim of this study is to (a) report on characteristics of bipolar disorder and co-occurring CUD; (b) examine rates of co-morbid mental disorders among individuals with bipolar disorder and CUD; (c) examine bipolar-related indicators of course of illness among individuals with bipolar disorder and CUD. We used data from the National Epidemiologic Survey on Alcohol and Related Conditions (NESARC) to examine the relationship between bipolar disorder and CUD. The NESARC is the largest epidemiological survey to-date on mental illness and substance abuse. In addition, it uses assessment tools which clearly differentiate primary mental disorders and substance-induced disorders. This is particularly important when exploring the association between bipolar disorder and CUD, as it is the only way to conclude whether CUD among individuals with bipolar disorder are associated with specific co-occurring mental disorders even when cannabis-induced mental disorders are ruled out.
Section snippets
Sample
We analyzed cross-sectional data from a population-based national representative sample, the National Epidemiological Survey of Alcohol and Related Conditions (NESARC) study (Wave 1, 2001–2002) (Grant et al., 2003b) conducted by the National Institute on Alcohol Abuse and Alcoholism (NIAAA). The interview was developed to advance measurement of substance use and mental disorders in large-scale surveys. Face-to-face interviews were conducted with 43,093 adults (response rate, 81%), aged 18 years
Results
Rates of 12-month CUD among individuals with lifetime bipolar disorder were 7.2% (CI=5.8–9.0), compared to 1.2% (CI=1.1–1.3) in the general population. Among individuals with CUD, no differences were found in the mean age of first use of cannabis (16.0 (±0.47) vs. 16.0 (±0.22); p=0.95), mean number of days of cannabis used in the last 12 months (192.1 (±16.9) vs. 161.1 (±7.0); p=0.09) and mean number of joints consumed on days when cannabis was used (3.2 (±0.41) vs. 2.6 (±0.17); p=0.13) among
Discussion
Cannabis use disorders are more prevalent among individuals with bipolar disorder compared to the general population. Results of this study show that among individuals with bipolar disorder, co-occurring CUD is associated with significant co-morbidities, particularly co-morbid substance use disorders. CUD among individuals with bipolar disorder was also found be associated with a more severe course of illness.
The general sociodemographic characteristics of individuals with CUD among respondents
Acknowledgments
This research was supported by a strategic training grant (Grant number TUF 96115) from the Canadian Institute of Health Research provided for the Social Aetiology of Mental Ilness Training Program.
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