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  WHO > Programmes and projects > World health report > The world health report 2001 - Mental Health: New Understanding, New Hope
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Chapter 2: Burden of Mental and Behavioural Disorders: Previous page | 1,2,3,4,5,6,7,8

Comorbidity

  Chapter 2

It is common for two or more mental disorders to occur together in an individual. This is not unlike the situation with physical disorders, which also tend to occur together much more frequently than can be explained by chance. It is especially common with advancing age, when a number of physical and mental disorders occur together. Physical health problems not only coexist with mental disorders such as depression, but can also predict the onset and persistence of depression (Geerlings et al. 2000).

One of the methodologically sound studies of a nationally representative sample was done in the United States (Kessler et al. 1994) and showed that 79% of all ill people were comorbid. In other words, only in 21% of patients did a mental disorder occur singly. More than half of all lifetime disorders occurred in 14% of the population. Similar findings have been obtained in studies from other countries, although not much information is available from developing countries.

Anxiety and depressive disorders commonly occur together. Such comorbidity is found among about half of all the individuals with these disorders (Zimmerman et al. 2000). Another common situation is the presence of mental disorders associated with substance use and dependence. Among those attending alcohol and drug services, between 30% and 90% have a "dual disorder" (Gossop et al. 1998). The rate of alcohol use disorders is also high among those attending mental health services (65% reported by Rachliesel et al. 1999). Alcohol use disorders are also common (12­50%) among persons with schizophrenia.

The presence of substantial comorbidity has serious implications for the identification, treatment and rehabilitation of affected individuals. The disability of individual sufferers and the burden on families also increase correspondingly.

Chapter 2: Burden of Mental and Behavioural Disorders: 1,2,3,4,5,6,7,8 | Next page

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