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6. CONCURRENT DISORDERS

CHAPTER 6

Concurrent Disorders

Introduction
Over the past decade, there has been increasing awareness that there is a
high degree of comorbidity (co-occurrence in the same individual) between
various psychiatric disorders. That is, individuals with a history of one
psychiatric disorder are much more likely than would be expected by chance
to have a history of another psychiatric disorder (Robins & Regier, 1991;
Kessler et al., 1994). Most relevant to this report are data indicating that there
is high comorbidity between any mental disorder and substance dependence.
Specifically, these data indicate that:
• Lifetime prevalence of alcohol disorder is 22.3% for individuals with
any mental disorder compared to 14% for the general population, and
that the odds of having an alcohol disorder if a person also has any
mental disorder are 2.3 times higher than if there is no mental disorder
(Regier et al., 1990).
• Among people with substance (except alcohol) use disorders, 53% also
suffer from at least one other mental disorder, with an odds ratio of 4.5
when compared to people without substance (other than alcohol)
disorders (Regier et al., 1990).

• Higher percentages of people with mental illness, particularly those
with schizophrenia, smoke tobacco than in the general population and
among people without mental illness. Depending on the particular
mental illness, it has been reported that 26–88% of psychiatric patients
smoke compared to 20–30% of the general population (Glassman et
al., 1990; Breslau, 1995; Hughes et al., 1986).
Despite the fact that the majority of studies were undertaken in a few
developed countries and the degree of comorbidity in many cultures is vastly
unknown, this high degree of comorbidity between mental disorders and
substance use disorders strongly suggests that these disorders are linked
because of shared neurobiological and behavioural abnormalities. Although
most scientists and clinicians would agree with this suggestion, it remains
unclear as to what the causal factors are. That is, does mental illness lead to
substance dependence, or does substance dependence lead to mental illness,
or are both mental illness and substance dependence independent

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