PHQ-9

The Patient Health Questionnaire-9 (PHQ-9) is a 9-item self-report instrument derived from the full PHQ designed to screen for, diagnose, and monitor the severity of major depressive disorder. Each item corresponds to one of the nine DSM-IV/DSM-5 criteria for major depression and is rated on a 0–3 scale (0 = not at all, 3 = nearly every day) over the past two weeks. Total scores range from 0 to 27. The PHQ-9 is the most widely used depression screener in clinical practice globally and is increasingly adopted as a secondary endpoint in psychedelic clinical trials due to its brevity, strong psychometric properties (sensitivity 88%, specificity 88% at cutoff ≥10), and free availability in the public domain. It correlates well with clinician-rated scales and is sensitive to treatment-related change.