Center research in 2010, using a PTSD rat model, has addressed need to seek a novel 5-HT2A receptor antagonist that can demonstrate maximum efficacy with minimum adverse reaction in the treatment of PTSD. In the center’s current research, administration of the novel 5-HT2A antagonist, MDL 11,939, administered within 30 minutes before or after exposure to traumatic stress, is hypothesized to prevent traumatic event-induced exaggerated fear response in an animal model of PTSD. The use of such compounds that act specifically at the 5-HT2A receptor would also be expected to prevent the undesirable side effects that occur in human subjects who are treated with selective serotonin reuptake inhibitors (e.g., SSRIs) and antidepressants. This research will benefit active duty military, reservists and veterans, as well as civilians exposed to traumatic circumstances.