In-session cortisol reactivity as a predictor of treatment response in Korean patients with PTSD.

Post-traumatic stress disorder (PTSD) is associated with hypothalamic-pituitary-adrenal (HPA) axis dysregulation, and in-session cortisol reactivity during exposure-based therapy may carry prognostic value. This study examined whether within-session salivary cortisol reactivity during Written Exposure Therapy (WET) predicts treatment response in Korean patients with PTSD. In a secondary analysis of a non-randomized waitlist-controlled trial (N = 41), cortisol was collected before and 15 min after the writing task at each of five sessions. Treatment response was defined using the reliable change index and assessed with the CAPS-5 and PCL-5 at the 6-week assessment, 12-week follow-up, and 24-week follow-up. Post-session cortisol suppression was numerically observed across all five sessions but reached significance only at Sessions 2 and 3. No significant group differences in Session 1 cortisol reactivity were found at the 6-week assessment; however, at 12-week follow-up responders showed significantly greater Session 1 cortisol suppression than non-responders on both CAPS-5 and PCL-5 (rs = 0.502 and 0.651, respectively), and this discrimination persisted at 24-week follow-up for PCL-5 (r = 0.563) but not CAPS-5. Subjective distress and cortisol reactivity were largely independent. These findings suggest that efficient HPA axis regulation during the first WET session may serve as an early biological marker of treatment consolidation.