Ketamine-Assisted Psychotherapy for Treatment-Resistant Depression

Proportion of Participants Retained in Study Through 2-Month Follow-Up

Retention will be assessed as completion of all scheduled study assessments through the 2-month follow-up. A single value is derived for each participant, coded as 1 (retained) or 0 (not retained). Higher values indicate successful retention; lower values indicate dropout.

Mean Change in Hamilton Depression Rating Scale (HDRS) Total Score

Depression severity will be measured using the 17-item HDRS (items scored 0-2 or 0-4; total score range 0-52). A single value is derived by summing item scores. Higher scores indicate greater depression severity (worsening); lower scores indicate reduced severity (improvement). Mean change is calculated as post-treatment score minus baseline score.

Mean Change in Numerical Pain Rating Scale Score

Pain intensity will be assessed using an 11-point Numeric Rating Scale (0 = no pain, 10 = worst imaginable pain). A single value is derived by averaging participant ratings at each time point. Higher scores indicate worse pain; lower scores indicate reduced pain. Mean change is calculated as follow-up score minus baseline score.

Mean Change in NEO Five-Factor Inventory-3 (NEO-FFI-3) Openness Subscale Score

Openness will be measured using the NEO-FFI-3 Openness subscale (12 items scored 0-4; total score range 0-48). A single value is derived by summing the 12 item scores. Higher scores indicate greater openness; lower scores indicate reduced openness. Mean change is calculated as follow-up score minus baseline score.

Mean Acceptability Rating of Ketamine-Assisted Psychotherapy

Acceptability will be assessed using a 5-point Likert scale (1 = low acceptability, 5 = high acceptability). A single value is derived by averaging scores across participants. Higher scores indicate greater acceptability; lower scores indicate lower acceptability.

Proportion of Participants Reporting Adverse Events (AEs)

Adverse events will be graded using the Common Terminology Criteria for Adverse Events (CTCAE v5.0; 0 = none, 1 = mild, 2 = moderate, 3 = severe, 4 = life-threatening, 5 = fatal). A single value is derived for each participant as the highest AE grade experienced. Higher values indicate more severe AEs; lower values indicate milder or no AEs.

Mean Mystical Experience Questionnaire (MEQ-30) Total Score

Mystical experiences will be measured using the MEQ-30 (30 items scored 0-5; total score range 0-150). A single value is derived by summing item scores. Higher scores indicate more intense mystical experiences; lower scores indicate fewer or weaker mystical experiences.

8. Mean Change in Resting-State fMRI Whole Brain Functional Connectivity

Functional connectivity will be measured using resting-state fMRI. Correlations between 400 cortical ROIs (Schaefer atlas) and subcortical ROIs (Harvard-Oxford atlas) will be calculated. A single value per participant is derived as the mean Fisher-Z transformed correlation coefficient across all ROI pairs. Higher values indicate stronger connectivity; lower values indicate weaker connectivity. Mean change is calculated as post-treatment value minus baseline value.

Mean Change in Subcortical Brain Volume

Volumes of subcortical structures will be calculated from MRI scans using FSL-FIRST and FreeSurfer. A single value per participant is derived by summing the volumes of predefined structures (mm³). Higher values indicate larger volumes; lower values indicate smaller volumes. Mean change is calculated as post-treatment volume minus baseline volume.

Clinician-Administered Dissociative States Scale (CADSS-6) Total Score

Dissociation will be measured using the CADSS-6 (6 items scored 0-4; total score range 0-24). A single value is derived by summing item scores. Higher scores indicate greater dissociation; lower scores indicate less dissociation.