depression: co-occurrence with other illnesses

Source: National Institute of Mental Health

Depression can coexist with other illnesses. In such cases, it is important that the depression and each co-occurring illness be appropriately diagnosed and treated.

Research has shown that anxiety disorders­which include post traumatic stress disorder (PTSD), obsessive compulsive disorder, panic disorder, social phobia, and generalized anxiety disorder­commonly accompany depression.

Depression is especially prevalent among people with PTSD, a debilitating condition that can develop after exposure to a terrifying event or ordeal in which grave physical harm occurred or was threatened. Traumatic events that can trigger PTSD include violent personal assaults such as rape or mugging, natural disasters, accidents, terrorism, and military combat. PTSD symptoms include: re experiencing the traumatic event in the form of flashback episodes, memories, or nightmares; emotional numbness; sleep disturbances; irritability; outbursts of anger; intense guilt; and avoidance of any reminders or thoughts of the ordeal. In one NIMH supported study, more than 40 percent of people with PTSD also had depression when evaluated at one month and four months following the traumatic event.

Substance use disorders (abuse or dependence) also frequently co-occur with depressive disorders. Research has revealed that people with alcoholism are almost twice as likely as those without alcoholism to also suffer from major depression. In addition, more than half of people with bipolar disorder type I (with severe mania) have a co-occurring substance use disorder.

Depression has been found to occur at a higher rate among people who have other serious illnesses such as heart disease, stroke, cancer, HIV, diabetes, and Parkinson’s. Symptoms of depression are sometimes mistaken for inevitable accompaniments to these other illnesses. However, research has shown that the co-occurring depression can and should be treated, and that in many cases treating the depression can also improve the outcome of the other illness.

Causes of Depression

Substantial evidence from neuroscience, genetics, and clinical investigation shows that depressive illnesses are disorders of the brain. However, the precise causes of these illnesses continue to be a matter of intense research.

Modern brain imaging technologies reveal that, in depression, neural circuits responsible for the regulation of moods, thinking, sleep, appetite, and behavior fail to function properly, and critical neurotransmitters­chemicals that brain cells use to communicate­ are out of balance. Studies of brain chemistry, including the effects of antidepressant medications, continue to inform our understanding of the biochemical processes involved in depression.

In some families, depressive disorders seem to occur generation after generation; however, they can also occur in people with no family history of these illnesses. Genetics research indicates that risk for depression results from the influence of multiple genes acting together with environmental or other non-genetic factors.

Very often, a combination of genetic, cognitive, and environmental factors is involved in the onset of a depressive disorder. Trauma, loss of a loved one, a difficult relationship, a financial problem, or any stressful change in life patterns, whether the change is unwelcome or desired, can trigger a depressive episode in vulnerable individuals. Later episodes of depression may occur without an obvious cause.

NIH Publication No. 05-4972
Revised 2005