Substance use disorders (SUD) and posttraumatic stress disorder (PTSD) are frequently comorbid in those who have experienced psychological trauma, although little research has investigated the cause and effect relationships between the two. This thesis examined the co-occurrence of trauma-related symptoms, PTSD, and SUD using Perceived Causal Relations scaling in an online community sample (n = 513) and in persons who were or had recently attended treatment for SUDs (n = 12). In both samples, participants perceived trauma-related reexperiencing and avoidance as significant causes of substance use partly dependent on the gender of the respondent, and men reported that dissociative experiences were more of an effect than a cause of their substance use. Study results are considered in respect to the self-medication, high-risk and susceptibility hypotheses associating PTSD-SUD comorbidity
