Ketamine and Nitroprusside for Depression

The purpose of this study is to test the effects of the medication ketamine and the medication called nitroprusside in patients with major depression. Ketamine has both good and bad effects. Some studies have shown that ketamine improves depression. However, studies have also shown that it causes strange and sometimes unpleasant sensations referred to "psychotic" or "dissociative" symptoms. An example of a psychotic symptom would be hearing or seeing something that in reality is not there. The study team would like to see if nitroprusside can prevent the reported bad effects of ketamine without blocking the reported good effects. This might make ketamine a better treatment for depression.