In the first session, one group of TRD patients receive low dose Ketamine (0.5 mg/kg) over 40 minutes while the other group of TRD patients receive placebo-saline infusion. In the second visit, the patients who received ketamine in the first visit will receive placebo-saline infusion and the patients who received placebo-saline infusion will receive a ketamine infusion. The study will be randomized such that in the first session, 5 patients will receive ketamine infusion and 5 patients will receive placebo. The randomization will be broken and the data analyzed. The study will then continue with the remaining 10 patients, where 5 of them will receive ketamine infusion and 5 patients will receive placebo infusion in the first session.