What is comorbidity ?

In medicine, comorbidity is the presence of one or more additional diseases or disorders co-occurring with a primary disease or disorder. The term can indicate either a condition existing simultaneously but independently with another condition or a related medical condition. Comorbidity also implies interactions between the illnesses that affect the course and prognosis of both.

‘Comorbidity’ was defined by Feinstein (1970) as “any distinct clinical entity that has co-existed or that may occur during the clinical course of a patient who has the index disease under study” (pp. 456 –7). Within psychiatry, comorbidity is commonly
used to refer to the overlap of two or more psychiatric disorders (Boyd, Burke, Gruenberg, et al., 1984). Comorbidity between substance use disorders and other mental disorders has gained increasing prominence in psychiatry and psychology within the past few decades (Wittchen, 1996). Angold and colleagues have recently drawn a distinction between two types of comorbidity (Angold, Costello, & Erkanli, 1999).
Homotypic comorbidityrefers to the co-occurrence of mental disorders within a diagnostic grouping (Angold et al., 1999). The co-occurrence of two different substance use disorders (e.g. cannabis and alcohol) is an example of homotypic
comorbidity. Heterotypic comorbidity refers to the co-occurrence of two disorders from different diagnostic groupings (Angold et al., 1999). This might include, for example, the co-occurrence of a substance use disorder and an anxiety disorder.

whatever is the definition, the final point is Comorbidity is associated with worse health outcomes, more complex clinical management, and increased health care costs. In the United States, about 80% of Medicare spending is devoted to patients with 4 or more chronic conditions, with costs increasing exponentially as the number of chronic conditions increases.