Posttraumatic stress disorder (PTSD) is the fourth most common psychiatric disorder and is estimated to affect more than ten million American children and adults at some point in their lives. Although a number of pre-, peri-, and acute phase post-trauma variables (e.g., prior trauma history, subjective life threat, injury) have been shown to increase one's risk of developing PTSD, initial psychological reaction to a traumatic event is an imperfect predictor of subsequent diagnosis. In addition, early psychological interventions have generally proven ineffective, and in some cases, detrimental with regards to subsequent symptomatology. In light of this, researchers have recently begun to examine possible pharmacological interventions that could be administered in the acute phase of responding to trauma to prevent or reduce the severity of subsequent post-traumatic stress.