There has been a resurgence of interest in hallucinogenic psychedelics (eg, psilocybin, lysergic acid diethylamide (LSD), mescaline, N,N-Dimethyltryptamine (DMT)) and entactogens (eg, 3, 4-methylenedioxymethamphetamine [MDMA]) in psychiatric research, which are hypothesized to achieve clinical benefit due to, in part, experiences of altered consciousness and fundamental shifts in mental frameworks.2
These drugs have been associated with cognitive states of enduring personal importance and have been compared with mystical experiences that might emerge over the ordinary course of life and carry sacred or spiritual meaning. Furthermore, these experiences may powerfully influence existential concepts of self, including moral values, self-identity, and purpose. There is converging evidence that these psychedelic effects are mediated in part by activity at 5HT-2A receptors. Ketamine may induce alterations in consciousness and personal frameworks similar to those achieved by serotonergic psychedelics while also sharing a common glutamatergic pathway of drug effect.3,4 However, there has been little investigation into how such changes might mediate the therapeutic potential of ketamine.
Preliminary data suggest that ketamine produces meaningful, transformative experiences that may help patients accept healthier values, behaviors, and beliefs related to abstinence from drugs and alcohol.5,6 Other evidence suggests that dose-related mystical-type experiences mediate the effects of ketamine on motivation to quit in cocaine-dependent research volunteers.7 Few recent studies have examined whether ketamine’s hallucinogenic properties are implicated in antidepressant effects; however, psychiatric vulnerabilities to depression plausibly involve an existential dimension. This dimension includes depressive symptoms of hopelessness, guilt, and suicidality, which appear to be ketamine-sensitive.8
Given the paucity of modern literature exploring the psychedelic and mystical properties of ketamine in depression, more widespread data on psychotomimetic and dissociative effects of ketamine provide some initial groundwork. Berman and collegeagues9 and Zarate and colleagues10 suggested that the antidepressant effects of ketamine (0.5 mg/kg over 40 min) were disconnected from ketamine-induced psychotomimetic symptoms. The antidepressant effects, measured by the Hamilton Depression Rating Scale (HDRS), were significant even after positive symptoms on the Brief Psychiatric Rating Scale (BPRS) returned to baseline. However, it was also noted that initial changes in BPRS positive symptom scales from baseline trended to predict a greater decrease in HDRS scores within a day of treatment with ketamine.
A small study further demonstrated a substantial relationship between psychotomimetic effects 30 minutes after ketamine administration (0.54mg/kg over 30 min) as measured by BPRS and antidepressant effects in the following week.11 A larger study involving 108 patients found that dissociation measured by the Clinician Administered Dissociative States Scale (CADDS) at 40 minutes was associated with HDRS score improvement at 230 minutes and 7 days after infusion.12 Although no relationship between initial BPRS positive subscale scores and antidepressant effect was found, a correlation between CADSS and BPRS scores was found at 40 minutes postinfusion.
Dr. Mathai is PGY 1 Psychiatry Resident, Dr. Mathew is Professor of Psychiatry, Dr. Storch is Professor of Psychiatry, and Dr. Kosten is Professor of Psychiatry, Baylor College of Medicine, Houston, TX.
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