Based on psychobiological assumptions regarding HPA dysregulations in stress-related disorders [25 (link),26 (link)], as well as findings from prior studies conducted by our own workgroup [27 (link)] and other researchers [28 (link)] we posited that subgroups of patients could be identified based on their unstimulated cortisol levels. Participants were fasted from the night before the morning blood sampling. They were asked to quietly relax before sample collection. Serum cortisol levels were measured using the Elecsys Cortisol II assay (Roche Diagnostics GmbH, Mannheim, Germany) at the Global Clinical Central Lab (Yongin, South Korea). Based on the median cortisol levels, participants were divided into low- vs. high-cortisol groups for analysis. Given the lack of an absolute cutoff value for cortisol levels and the goal of maximizing statistical power by increasing the number of patients in both groups, we divided the two groups based on the median cortisol value, as we have previously done in a similar study [27 (link)].