Among people with treatment-resistant depression, the intensity of dissociation caused by a single infusion of ketamine or esketamine is linked to greater antidepressant effect one day later, but only when dissociative symptoms are mild to moderate. For every one-point increase on a dissociation scale up to 15 points, depression scores improved by an average of 0.5 points after 24 hours. This relationship was not observed at 72 hours or 7 days after infusion. The study was not originally designed to test this relationship, so confounding factors were not controlled, and the finding should be considered suggestive rather than definitive.
A systematic review of 46 studies on ketamine and its enantiomers for major depressive disorder identified 16 assessment tools used to measure suicidal behavior. Most were explicit, clinician-rated scales such as the Montgomery-Åsberg Depression Rating Scale (MADRS), Hamilton Depression Rating Scale (HAM-D), and Beck Scales for Suicide Ideation. Only the Suicide Ideation and Behavior Assessment Tool (SIBAT) was specifically developed for rapid-acting antidepressant trials. The variety of instruments used across studies makes comparisons difficult. The MADRS is suggested as a reasonable choice for assessing suicidal behavior in this context, though no single tool is universally preferable.