I . The recommended treatments for post-traumatic stress disorder (PTSD) are psychological therapies and medication, but the best approach is still discussed. Exposure to traumatic events in psychotherapy tends to cause high drop- out rates. Likewise, little effect or adverse events of medications may lead to attrition. The aim of this study was to compare the outcomes of treatment by psychotherapy and medications. An additional aim was to explore the combinations of treatment modalities in adults with PTSD and to investigate differences in drop-out rates. METHODS M . A systematic review was performed in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-Analysis (PRISMA) statement. PubMed and Embase were searched for relevant randomised clinical trials. The Cochrane risk-of-bias tool was used to assess the quality of the retrieved trials. RESULTS R . Seven eligible studies were identified. Three studies showed that psychotherapy was superior to selective serotonin reuptake inhibitors. Two studies showed an augmenting effect with prolonged exposure. Two studies showed no differences across the treatment groups. In four of the included studies, patients treated with psychotherapy were more likely to drop out. CONCLUSIONS C . Extant evidence is insufficient to assess whether combined therapy is superior to monotherapy. Both medication and psychotherapy have an effect on PTSD, but psychotherapy tends to provide greater and more long-lasting outcome improvements. Trauma type, PTSD severity and other variables affect drop-out rates and treatment outcomes.