Sexual dysfunction is a common side effect of selective serotonin reuptake inhibitors (SSRIs). The hypotheses of this study are that:1. subjects with major depression or dysthymia who are being treated with an SSRI and experiencing treatment-related sexual dysfunction will experience less sexual dysfunction if they are switched to duloxetine, and 2. they will experience either improved antidepressant response or no loss of antidepressant response.