The problem with prescription medications for PTSD (post traumatic stress disorder) is that they are not as effective as they are for the other major anxiety disorders. PTSD is a severe manifestation of anxiety, where you are re-living the trauma you endured through flashbacks and nightmares of the event. So you are being traumatized over and over again with this disorder. As you recall the traumatic events, you become hypervigilant and constantly scan your environment for any sign of danger, to protect yourself. And why not? You are reliving the traumatic events in your mind as if they were still happening, so this is a very distressing state. So you are hypervigilant, on guard constantly, having your sleep disrupted by nightmares, and your days filled with flashback of the horrible event. Monotherapy with an antidepressant just does not work much of the time...often need to find combinations of medications to address the multiple problems and symptoms seen with PTSD, and these symptoms encompass anxiety, mood lability, sleep, recall of the trauma, and hypervigilance. Therefore multiple medications are commonly required to address all these symptoms in multiple domains.