In treatment-resistant inpatients with major depressive or bipolar disorder, the dissociative side effects of a single ketamine infusion predicted a more robust and sustained antidepressant response. Greater dissociation measured 40 minutes after infusion correlated with greater improvement in depression scores at 230 minutes and 7 days later. In contrast, psychotomimetic symptoms, manic symptoms, and changes in blood pressure or pulse were not significantly linked to antidepressant efficacy. The findings suggest that dissociation, rather than other side effects, may be a marker or mediator of ketamine's antidepressant action, though further prospective research is needed.
Higher body mass index and a family history of alcohol use disorder in a first-degree relative were associated with greater improvement in depression symptoms after a single ketamine infusion. Patients with no prior suicide attempts also showed greater improvement, but only at day 7. The analysis combined data from four studies of treatment-resistant inpatients with major depressive disorder or bipolar depression who received a single 0.5 mg/kg ketamine infusion over 40 minutes. The findings suggest that certain clinical characteristics may help predict who benefits most from ketamine's rapid antidepressant effects, though the analysis was post hoc and the models explained only 13% to 36% of the variation in symptom improvement.