Understanding comorbidity between substance use, anxiety and affective disorders: Broadening the research base
Section snippets
Comorbidity: beyond specialist health services
Schizophrenia and bipolar disorder have been given an understandably high priority by those in the specialist mental health system who have to treat the distress and disability that these disorders cause. People with dual diagnoses are less likely than persons with psychosis alone to comply with medication, and more likely to experience psychosocial problems, depression, suicidal behaviour, rehospitalisation, homelessness, and higher family burden (Bartels et al., 1992, Drake et al., 1996).
What have population studies shown?
The richest epidemiological data on patterns of comorbidity comes from surveys in the USA such as the National Comorbidity Survey (NCS) in the early 1990s (Kessler et al., 1994), its replication (NCS-R) in 2001–2002 (Kessler, Chiu, Demler, Merikangas & Walters, 2005) and the National Epidemiological Survey on Alcohol and Related Conditions (NESARC) (Compton et al., 2007, Hasin et al., 2007). Similar studies have also been conducted in other developed countries including Australia (The National
Why does comorbidity matter?
Comorbidity matters for several important reasons. First, it is the rule rather than the exception with mental disorders; if we ignore comorbid disorders when studying one type of mental disorder, we may mistake characteristics of the disorder under study for those of comorbid conditions (Kessler, 1995, Kessler and Wang, 2008).
Second, persons with comorbid mental disorders often have a poorer treatment response and a worse course of illness over time (Kessler, 1995, Kavanagh et al., 2003),
Understanding comorbidity
There are a number of hypotheses that may explain the comorbidity between substance use and anxiety and affective disorders (Cerda et al., 2008, Kessler and Wang, 2008). These have very different implications for treatment and prevention of psychiatric comorbidity.
First, one mental disorder may directly produce another e.g. sustained heavy alcohol abuse can produce depression in persons who are alcohol dependent (Raimo & Schuckit, 1998).
A second possibility is that some mental disorders may
Prospective epidemiological studies
Hypotheses about the nature of the relationships between comorbid disorders cannot be clearly distinguished in cross-sectional epidemiological studies that use retrospective life histories to assess temporal and causal relationships between disorders. More direct tests are needed using longitudinal studies of mental disorders (e.g. Fergusson & Horwood, 1997) in representative population samples to minimise the selection bias that affects treatment samples. To date a limited number of such
Conclusions
The central foci of research to date on comorbidity between substance use disorders and other mental disorders have been on epidemiological studies of the prevalence and correlates of comorbidity in the population and small scale clinical studies of the outcome of combined pharmacological and psychological interventions for patients with the comorbid alcohol and anxiety and depressive disorders, psychosis and substance use disorders. The epidemiological research has provided important
Acknowledgement
We would like to thank Sarah Yeates for her assistance in searching the literature and preparing this paper for publication.
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