Personality moderates the predictive value of serum serotonin for antidepressant remission in depressive disorders.

Blood-based biomarkers such as peripheral serotonin (5-HT) hold promise for predicting antidepressant response in depression, but findings have been inconsistent. Personality traits linked to serotonergic function may moderate this relationship. This study examined whether personality type (PT) moderates the relationship between baseline serum serotonin (s5-HT) levels and antidepressant remission at 12 weeks. In a prospective, naturalistic study, 1086 outpatients with depressive disorders received stepwise pharmacotherapy. PT was classified as resilient or vulnerable using cluster analysis of the Big Five Inventory. Baseline s5-HT was measured and analyzed as both categorical (median split) and continuous variables. Remission was defined as a Hamilton Depression Rating Scale (HAMD) score ≤ 7 at week 12. Logistic regression tested the main and interaction effects of PT and s5-HT, adjusting for covariates. No direct association was found between PT and s5-HT levels. However, higher s5-HT significantly predicted remission only in the resilient group, showing a significant PT × s5-HT interaction. These findings identify personality as a moderator of the relationship between peripheral serotonin and antidepressant response. This biopsychosocial interaction may help explain prior inconsistencies and may provide preliminary insights relevant to individualized care, pending further validation.