In the inpatient trial, patients will be randomly assigned to receive ketamine or placebo for the duration of the acute ECT course. Patients will be administered a detailed cognitive battery the day before commencing ECT treatment, the day after the 6th treatment, and 1-3 days and 1 month following the end of the acute ECT course. The purpose of this trial is to examine whether patients in the ketamine condition had superior cognitive outcomes to those in the placebo condition during and following a course of ECT. In addition, depressive symptomatology will be examined throughout the ECT course to determine whether ketamine anaesthesia during ECT has antidepressant, as well as, cognitive benefits. Projected sample for this trial is N = 34.