Ketamine and its enantiomers show different abuse liability. Preclinical evidence indicates that (R,S)-ketamine and (S)-ketamine carry greater risk for abuse than (R)-ketamine, which at antidepressant-relevant doses in rodents appears safe with minimal liability. In clinical settings, limited studies suggest that single or repeated ketamine administrations under professional control did not lead to misuse, dependence, diversion, or gateway activity in patients with treatment-resistant depression. However, most clinical studies were retrospective and lacked systematic evaluation with validated scales. The review identified 65 eligible studies (55 preclinical, 10 clinical), with only 4 preclinical studies evaluating enantiomer abuse liability.
Psychotic depression, a severe form of major depression with hallucinations or delusions, affects 0.35-1% of people over a lifetime. Current treatments, such as antidepressants combined with antipsychotics or electroconvulsive therapy, often lead to relapse and side effects like tardive dyskinesia. Some case studies suggest ketamine may improve both mood and psychotic symptoms in treatment-resistant patients, but its safety is debated because ketamine can induce psychotomimetic effects. Most clinical trials have excluded these patients, so it remains unknown whether ketamine would worsen psychosis. Future research should include people with psychotic features to determine ketamine's safety and effectiveness.