Major depressive disorder (MDD) is a recurrent, incapacitating psychiatric illness which will be the second most disabling disease worldwide by the year 2020. There is a rising promise in a N-methyl-D-aspartate (NMDA) receptor antagonist, ketamine, which may be used in the treatment of resistant depression. Many of the studies are in favor of the drug, even in single dose application, with effects appearing in minutes to hours from administration. However, there is a need to evaluate the benefits and risks regarding psychomimetic, psychiatric, neurologic, and cognitive adverse effects of ketamine administration. The most distressing symptoms which appear most frequently during ketamine administration are dissociative symptoms, which can be quantified as a CNS adverse drug reaction. Results generally show that a single infusion of ketamine is efficacious and well-tolerated, while dissociative symptoms tend to abate within 2 hours after ketamine administration. As studies show single doses of ketamine should be definitely considered as an option in TRD patients with/without suicidal thoughts, even though it could not provide remission, or the effect could be temporary, but improving patients' quality of life by reducing depressive symptomatology should be a major asset while considering this particular procedure, particularly in inpatients.