Comorbidity is the presence of one or more diseases in conjunction with a disease currently being studied or treated. For example, if a person sought treatment for schizophrenia but also had heart disease, his/her therapist or psychiatrist might say that his/her heart disease is comorbid with his/her schizophrenia.

Understanding Comorbidity
The term comorbidity has historically been used to characterize diseases that are unrelated to and neither cause nor are caused by the disease being treated. However, some medical professionals use the term more broadly to refer to all diseases a person has or even to indicate that one disease is affecting the other; while increasingly common, this use is less standard.

The concept of comorbidity helps treatment providers to understand the total impact of all diseases on a person’s life. It can also help with treatment decisions. For example, some psychoactive medications can exacerbate heart conditions by increasing the blood pressure or pulse, so when a mental health patient has a comorbid condition, treatment providers generally take into account the net effect.

Comorbidity in Psychology
In the field of psychology, patients sometimes have several different physical or mental health conditions. Occasionally, the onset of a physical condition can contribute to the development of a mental health condition. For example, a person with lung cancer might develop depression; when a doctor describes the depression as comorbid, the doctor is using the term to mean that the condition is related.

Comorbidity can affect a person’s prognosis because other illnesses affect the medications a person can take, the effectiveness of these medications, and the long-term success of treatment. For example, a young, otherwise healthy person might be more likely to recover from cancer than someone with several comorbid conditions, any of which can exacerbate or be exacerbated by the cancer.


  1. Valderas, J. M., Starfield, B., Sibbald, B., Salisbury, C., & Roland, M. (2009). Defining Comorbidity: Implications for Understanding Health and Health Services. The Annals of Family Medicine, 7(4), 357-363. doi: 10.1370/afm.983

Last Updated: 08-4-2015

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