To feel anxious at times is normal, and all people experience it now and then. However, showing extreme, unreasonable, and constant anxiousness and fear about things is a psychiatric illness, medically termed as an anxiety disorder.

Anxiety disorders include obsessive compulsive disorder, panic disorder, social anxiety disorder, post-traumatic stress disorder, and so on. The most common anxiety disorder is generalized anxiety disorder (GAD). Many people are affected by more than one anxiety disorder concurrently, known as comorbidity. Surveys have shown that GAD is the most comorbid of anxiety disorders.

The coexistence or overlap of disorders increases the complexities of diagnosis and treatment for both the psychiatrist and the patient.

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Comorbidities of GAD

The most common comorbidities of GAD are major depressive disorder (MDD), bipolar disorder (BD), and substance use disorder (SUD), due to the similar symptoms of these disorders.

GAD and Major Depressive Disorder

GAD presents with uncontrolled and persistent worry about a range of things like job, family, and financial status. It is a kind of floating condition, where the person drifts from one worry to the next without end in such as way that it has an impact on their normal activities. MDD, often simply referred to as depression or clinical depression, is a serious mood disorder that also affects normal life. Patients with anxiety from a very young age, displaying low self-esteem, pessimism, and severe stress is accompanied by perpetual feelings of sadness or loss of interest over a long duration of time (more than 2 weeks in order for a diagnosis to be made).

Patients at both initial and severe stages of GAD have episodes of depression (MDD). Longitudinal studies have found variations in the appearance of MDD in patients with GAD. In these studies, (a) one-third of patients showed signs of GAD leading to MDD; (b) one-third had symptoms of MDD leading to GAD; and finally (c) one-third of them had the onset of both GAD and MDD simultaneously. More than 70% of patients with lifetime GAD are also found to have lifetime MDD. Studies of twins have revealed that the same genetic factors of risk have a hand in both GAD and MDD. However, whether the patient develops GAD or MDD first depends on how they react to the environmental stressors in their life.

GAD and Bipolar Disorder

Formerly called manic depression, bipolar disorder is characterized by extreme mood variations, from high to low; at high, the patient is over-exultant, while at low he may harbor suicidal thoughts for no particular reason. It has been found that 51% of patients with BD have another anxiety disorder, which actually worsens the illness. Due to this comorbidity, BD patients tend to have:

• Younger age of onset
• Lower quality of life
• Lower chance of recovery
• Increased risk of substance abuse, and, most importantly
• Greater lifetime suicidal tendencies

The average period of euthymia (normal positive state of mind) in BD with comorbid GAD is found to be less than half of that in patients with BD alone. Surveys have shown suicide attempts of 62% and 53% in BD and current and lifetime GAD comorbidity patients, respectively, as opposed to 22% in patients with BD alone.

Impulsiveness tends to be heightened in BD and current GAD patients, even after adjustments are made for age, gender, and presence of other comorbid anxieties.

GAD and Substance Use Disorder

Research studies have shown a significant link between patients of GAD and substance use or abuse. Most people with GAD are unaware of their illness and try to ease their anxiety by self-medication using alcohol or drugs.
One-third of individuals with GAD are victims of SUD, though they are mostly known to use and not abuse substances. A mutual pattern exists between these two disorders, which follow three pathways:

• Anxiety leading to substance use
• Substance use/abuse leading to anxiety
• Genetic risks that are central to both GAD and SUD.

A survey carried out in the USA had an odds ratio of 9:5 for dependence on drugs in the presence of GAD.

Future Directions

In spite of the extremely high rate of comorbidity, only half of the patients with GAD receive treatment, suggesting that the other half is probably resorting to self-medication. According to estimates, in the USA alone about 3.1% of adults met the criteria for GAD in 2016. More women are said to be affected by GAD, though the reason for this is unknown.

Psychiatrists are still at crossroads as to how they should approach treatment considerations, and whether to treat each disorder separately or in parallel? Should treatment for one be completed and then the next one started? Future research on the standard clinical care for comorbidities of anxiety disorders should be undertaken to explore this issue further.