Depression is a leading global public health concern, with trauma and trauma-related symptoms increasingly recognized as important contributors to its onset and maintenance. It remains unclear which specific post-traumatic and dissociative symptoms most strongly predict subsequent depressive symptoms.

This longitudinal study addressed this gap by examining the predictive role of complex PTSD and dissociative symptoms on depressive symptoms over six months.

Participants were 293 female mental health service users recruited internationally. They completed surveys at baseline and six-month follow-up. Measures included the Patient Health Questionnaire-9 (PHQ-9) for depressive symptoms, the International Trauma Questionnaire (ITQ) for ICD-11 complex PTSD symptoms, and the Multiscale Dissociation Inventory (MDI) for dissociative symptoms.

Controlling for baseline depression, age, education, and location, hierarchical multiple regression analysis revealed that baseline re-experiencing symptoms (β = 0.135, p = .019) and depersonalization (β = 0.187, p = .034) significantly and positively predicted follow-up depressive symptoms. Nevertheless, baseline avoidance was negatively associated with depressive symptoms (β = -0.304, p = .043) at follow-up.

These findings suggest that the trauma model of depression requires more research and replication. Re-experiencing, depersonalization, and avoidance might be important symptom-level targets for preventing and treating depression, but future research should replicate these patterns in larger and more diverse samples, examine the mechanisms linking trauma-related symptoms to depressive trajectories, and evaluate whether trauma-focused interventions reduce depressive symptoms in individuals with prominent re-experiencing and depersonalization.