Lisdexamfetamine Dimesylate in Residual Symptoms and Cognitive Impairment in Major Depressive Disorder.

This study aims to test the effect of a newly-approved stimulant medication, lisdexamfetamine dimesylate (Vyvanse), on specific residual symptoms of depression found in some patients who are undergoing treatment with, but have only partially responded to, a selective-serotonin reuptake inhibitor (SSRI) or selective-norepinephrine reuptake inhibitor (SNRI) antidepressant. Specifically, the investigators hypothesize that symptoms potentially related to deficient dopaminergic activity, such as lassitude, apathy, reduced positive affect and impaired executive function, in particular, will improve. This protocol is designed to test the hypothesis that this cluster of co-occurring residual symptoms sometimes found in treated depression will respond as a group to adjunctive psychostimulant therapy. The investigators propose to demonstrate this cluster of residual depressive symptoms and to measure the effect of stimulant therapy on it. The investigators hope to better understand the specific symptoms in this clinical population that are likely to improve with stimulant therapy.