There is considerable symptom overlap and high levels of comorbidity between anxiety disorders and depression. The recognition of this comorbidity has both academic interest and clinical significance. Epidemiological studies have demonstrated that depressed individuals with a history of anxiety disorders are at increased risk for hospitalization, suicide attempt, and greater impairment from the depression. These individuals also tend to have a more chronic course of depression, as observed in psychiatric patients, primary care patients, and epidemiological samples. Van Valkenberg and colleagues reported that depressed patients with anxiety had poorer outcome and greater psychosocial impairment than those without an anxiety disorder. In the National Institute of Mental Health Collaborative Depression Study, the presence of panic attacks predicted a lower rate of recovery during the first 2 years of the follow-up interval. Similarly, Grunhaus found poorer outcome in depressed patients with comorbid panic disorder than in depressed patients without panic. In an 8-month follow-up study, depressed primary care patients with a history of generalized anxiety disorder (GAD) or panic disorder were less likely to have recovered from their depressive episode.

Gaynes and colleagues prospectively followed primary care patients with major depressive disorder (MDD) every 3 months for 1 year after their initial diagnostic evaluation. At baseline, half of the original 85 patients had a coexisting anxiety disorder, the most frequent being social phobia (n=38). Twelve months after intake, 68 of the patients were available for the final interview. Those with a comorbid anxiety disorder were significantly more likely to still be in an episode of depression (82% vs 57%; risk ratio=1.44; 95% CI 1.02-2.04), and they experienced more disability days during the course of the 12 months than the depressed patients without an anxiety disorder (67.1 days vs 27.5 days).