Number of episodes and antidepressant response in major depression.

Current series of depression suggests that episodes of major depression sensitize a patient to further episodes so that the illness adopts a recurrent course. This suggested pathophysiological process may also lead to increased risk of treatment resistance and a chronic course of illness. This hypothesis has received little empirical support and, if correct, would suggest that greater number of episodes would lead to a decreased response to antidepressants. We examined this in a cohort of outpatients with major depressive disorder. We observed that initial severity of depression and duration of treatment, but not number of previous episodes, was related to treatment outcome. Our findings are discussed in relation to prevailing theories of the pathophysiology of depression and suggestions for further studies are made.