<qa>  What is the main cause of PTSD?PTSD is a common disorder with 10 lifetime prevalence among Americans. The major causes of PTSD are sexual assault, accidents, disasters Despite this public health burden, only two drugs, sertraline Zoloft and paroxetine Paxil, are approved by the FDA for the treatment of PTSD. New options for the treatment of PTSD are much needed. Approximately half of patients with PTSD respond to Zoloft and Paxil. Many patients experience psychotic symptoms with PTSD, which may not respond to treatment to Zoloft and Paxil. 