When a person experiences two or more illnesses at the same time, those illnesses are considered “comorbid.” This concept has become the rule, not the exception, in many areas of medicine, and certainly in psychiatry. Up to 93% of Medicare dollars are spent on patients with four or more comorbid disorders. The concept of comorbidity is widely realized but unfortunately not well-defined or understood.

In mental health, one of the more common comorbidities is that of depression and anxiety. Some estimates show that 60% of those with anxiety will also have symptoms of depression, and the numbers are similar for those with depression also experiencing anxiety.

While we don’t know for certain why depression and anxiety are so often paired together, there are several theories. One theory is that the two conditions have similar biological mechanisms in the brain, so they are therefore more likely to “show up” together. Another theory is that they have many overlapping symptoms, so people frequently meet the criteria for both diagnoses (an example of this might be the problems with sleep seen in both generalized anxiety and major depressive disorder). Additionally, these conditions often present simultaneously when a person is triggered by an external stressor or stressors.

While clinicians can typically recognize one mental illness relatively easily, it’s much more difficult to recognize comorbid disease. They must pay careful attention to symptoms that could suggest other disorders such as bipolar disorder and look for other factors such as substance abuse. This requires time with the patient, possibly their families and other collateral sources of information. The health care system today makes this level of assessment difficult, but not impossible.

Unfortunately, most research today focuses on patients with one illness, and treatments are then guided by this research. In result, there are many well-researched treatments available for mental illnesses, but not for comorbid mental illnesses. There is a lot that we still need to understand about how we recognize and treat conditions when they present at the same time.

There are several things we do know about comorbid anxiety and depression, however, and they underscore this need for accurate assessment. When anxiety and depression present together, these illnesses can often be harder to treat. This is because both the anxiety and depression symptoms tend to be more persistent and intense when “working” together.

This means that those experiencing both anxiety and depression will need better, more specialized treatments. Professionals and caregivers providing treatment may need to get creative, like adding one treatment onto another to make sure that both underlying disorders are responding. For example, if antidepressants are helping improve a person’s mood, but not their anxiety, a next step would be to add cognitive behavioral therapy to the treatment plan.

More research is needed to fully understand why some patients experience comorbid conditions and others do not. Until then, it is vitally important that those experiencing one, two or multiple mental illnesses engage in treatment early, and find a provider they can work with to reach their goals. While treatment may have more challenges when dealing with comorbidity, success is possible.

By Beth Salcedo, MD