PTSD'S mediation of the relationships between trauma, depression, substance abuse, mental health, and physical health in individuals with severe mental illness: evaluating a comprehensive model.

OBJECTIVE: Following trauma exposure and PTSD, individuals with severe mental illness (SMI) frequently suffer a complex course of recovery complicated by reduced mental and physical health and increased substance abuse. The authors evaluated a theoretical PTSD-SMI model which theorizes that trauma, PTSD, depression, substance abuse, mental health, and physical health are interrelated and that PTSD mediates these relationships. METHOD: Participants were ethnoracially diverse individuals diagnosed with SMI (N=175) who were assessed for trauma exposure, severity of PTSD and depression, substance abuse, and overall mental and physical health functioning. Pearson's correlations were utilized to examine the relationships between study domains. The mediating effects of PTSD were assessed using regression coefficients and the Sobel test for mediation. RESULTS: A majority of participants with SMI (89%) reported trauma exposure and 41% reported meeting diagnostic criteria for PTSD. On average, participants were exposed to over four types of traumatic events. Trauma, severity of PTSD and depression, substance abuse, and overall mental and physical health functioning were significantly interrelated. PTSD partially mediated the relationships between trauma and severity of depression and between trauma and overall mental health; PTSD fully mediated the trauma and overall physical health relationship. DISCUSSION: Within an ethnoracially diverse SMI sample, trauma exposure and PTSD comorbidity were high and associated with severity of depression, substance abuse, overall mental health and physical health functioning. Supporting our theoretical PTSD-SMI model, PTSD mediated the adverse effects of trauma exposure on participants' current severity of depression and overall mental and physical health functioning.