The relationship between subjective effects induced by a single dose of ketamine and treatment response in patients with major depressive disorder: A systematic review

Objective The relationship between ketamine's hallucinogenic- and dissociative-type effects and antidepressant mechanism of action is poorly understood. This paper reviewed the correlation between subjective effects defined by various psychometric scales and observed clinical outcomes in the treatment of patients with Major Depressive Disorder ( MDD ). Methods Based on PRISMA guidelines, we reviewed the dissociative and psychotomimetic mental state induced with ketamine during MDD treatment. Our selected studies correlated depression rating with validated scales collected at regular intervals throughout the study period such as the Clinician-Administered Dissociative States Scale (CADSS), Brief Psychiatric Rating Scale (BPRS), and the 5-Dimensional Altered States of Consciousness Rating Scale (5D-ASC). We excluded studies with bipolar depression or with repeated dosing and no single-dose phase. We included 8 of 556 screened reports. Results Two of five CADSS studies found significant negative correlations between increases in CADSS scores and depression scores. One of six BPRS studies demonstrated correlations between BPRS scores and depression scores. The 5D-ASC's one study found no correlation with the MADRS. Conclusions Ketamine's dissociative and psychotomimetic effects were correlated with depression changes in 37.5% of studies, but most studies did not examine this relationship and future studies should consider this association since it appears important for MDMA and psilocybin therapies.