Abstract

Background
Although the temporary antidepressant effects of the atypical psychedelic ketamine are well established, it is still controversially discussed whether ketamine’s acute psychoactive effects mediate the primary antidepressant response. Concerns have already been raised that the widely used dissociation questionnaires may not capture a depressed patient’s subjective ketamine experience with sufficient conceptual depth. Additionally, also standardized altered-states-of-consciousness (ASC) questionnaires have in their development not taken the actual ketamine experience of individuals suffering from depression into account.

Aims
We aimed to complement current ASC psychometrics in order to capture the ketamine experience and its antidepressant and therapy-assisting potential more fully. For this, we derived 11 new ASC questionnaire items based on qualitative reports of the ketamine experience from individuals suffering from depression. We hypothesize that these new items reveal important new relations between ketamine induced ASCs and antidepressant effects.

Methods
The 11 new items were measured with 14 patients suffering from depression with recurrent major depressive episodes (56 measured ketamine sessions) in an open-label, prospective, non-interventional, outpatient study. We added the new items to the latest psychometric 11-subscale version of the 5-Dimensional Altered State of Consciousness Rating Scale (5D-ASC) and analyzed the sensitivity with which the new items captured ketamine-induced ASCs and potential antidepressant effects when compared against the 5D-ASC.

Results
For 10 of the 11 new items, we found a strong correlation between their scores and the antidepressant treatment outcome. We also found generally strong effects for experienced ASCs: The stronger the ASCs overall, the stronger the resulting antidepressant effect. The two new items which showed the strongest correlation were: “In my mind problems of mine were treated so that it felt like a self-therapy” and “I was in a state that made me unsusceptible to mental problems.” These results clearly indicate the therapeutic potential of the ASC scale expansion.

Conclusion
Our study results suggest that our new qualitatively derived ASC items are sensitive to the ketamine experience and its antidepressant potential, and are therefore a valuable extension to the 5D-ASC for both research and therapy of depressed individuals.