Ketamine start relieving the symptoms of depression fairly quickly, sometimes after only one session unlike antidepressants that take several weeks to start working. Multiple clinical trials suggest that a single low dose (0.5mg/kg) of IV ketamine results in a 50–70% response rate in patients with treatment resistant depression. Wan L, Levitch CF, Perez AM, et al. Ketamine safety and tolerability in clinical trials for treatment resistant depression. J Clin Psychiatry 2015;76:247–52.
Researchers aren’t sure exactly why ketamine helps depression but one theory is that ketamine stimulates connections to regrow between brain cells that are involved in mood regulation. The blockade of NMDA-type glutamate receptors may also be a mechanism of action as Ketamine is a glutamate N-methyl-d-aspartate (NMDA) receptor antagonist.
Depression of Bipolar DIsorder also improves afer ketamine therapy and IV ketamine was also reported as efficacious in the treatment of PTSD. Feder A, Parides MK, Murrough JW, et al. Efficacy of intravenous ketamine for treatment of chronic posttraumatic stress disorder: a randomized clinical trial. JAMA Psychiatry 2014;71:681–8.
Some studies also show that the cognitive impairment (forgetfulness, lack of concentration) associated with severe depression can be improved by ketamine. Chen MH, Li CT, Lin WC, et al. Cognitive function of patients with treatment-resistent depression after a single low dose of ketamine infusion. J Affect Disord. 2018; 241:1-7.