--- - |2 The vast majority of adults in the United States experience at least one traumatic event during childhood. According to the self‐medication hypothesis of substance use disorders, adult survivors of childhood trauma may cope with trauma‐related symptoms via alcohol or drug use. The purpose of this study is to identify through which specific PTSD symptom clusters childhood trauma exposure are associated with adult substance use. Participants of this study (N = 627) were not recruited based on substance use or traumatic exposure. Results of this study demonstrate that arousal/reactivity partially mediates the association between childhood trauma and current substance use. Implications for treatment include recommendations for trauma‐informed approaches that aim to decrease arousal/reactivity and subsequently substance use. - Journal of Marital and Family Therapy, EarlyView.