Clinical features of treatment-resistant depression.

As many as 30% to 40% of patients with major depressive disorder are unresponsive to a trial of antidepressant medication. Many patients labeled with treatment-resistant depression actually have pseudoresistance, in that they have been inadequately treated or are misdiagnosed. Others may have unrecognized comorbid psychiatric or general medical conditions that contribute to treatment resistance. Variables such as gender, family history, age at onset, severity, and chronicity have also been evaluated as possible risk factors for treatment-resistant depression. This article reviews the current literature regarding the clinical characteristics of treatment-resistant depression, with particular attention to the relevance of these factors for clinical decision making.