There is growing evidence demonstrating rapid effectiveness onset of action (within hours) of intravenous administration of ketamine in depression, treatment-resistant depression and bipolar depression. Published review in Science (2012) by Duman & Aghajanian calls this “perhaps the most important discovery in half a century.” There is recent evidence published in JAMA Psychiatry (2013) by Hallak and colleagues provide evidence that sodium nitroprusside (SNP) given by intravenous route to patients diagnosed with schizophrenia improved psychosis within hours. Although the “precise” mechanism of action of both ketamine (in depression) and SNP (in schizophrenia) remain unclear but there is evidence indicating for the possible involvement of the “NMDA-Nitric Oxide-cGMP” pathway in mechanisms of action of these two rapid-onset effective therapeutic interventions.