Mechanisms of change in psychological interventions for posttraumatic stress symptoms: A systematic review with recommendations

Psychological interventions can alleviate posttraumatic stress symptoms (PTSS). However, further development of treatment approaches calls for understanding the mechanisms of change through which diverse interventions affect PTSS. We systematically searched the literature for controlled studies of mechanisms of change in psychological interventions for PTSS. We aimed to detect all empirically studied mechanisms and evaluate the level of evidence for their role in the alleviation of PTSS. We identified 34 studies, of which nine were among children. We found evidence for improvements in maladaptive posttraumatic cognitions as a general mechanism of change involved in diverse interventions, among both adults and children. We also found some preliminary evidence for increases in mindfulness as a mechanism of change in mindfulness- and spiritually-oriented interventions among adults. We found scant, mixed empirical evidence for other mechanisms of change. Notably, studies on changes in traumatic memories as a mechanism of change were lacking, despite clinical emphasis on their importance. A major limitation across reviewed studies was that most could not establish temporal order of changes in mechanisms and PTSS. Including thorough analyses of mechanisms of change beyond cognitions in all future trials and improving the reporting of findings would aid the development and implementation of even more effective interventions.