Current research efforts are exploring the underlying neurochemical changes associated with PTSD. Recently, these efforts have focused on the prevention of PTSD in persons exposed to trauma by administration of medication to affect the underlying neurochemical processes. For example, preliminary evidence suggests that interference with consolidation of trauma-related memories using the beta-antagonist, propranalol, may prevent PTSD in humans with recent traumas. However, given that as much as 90% of the US population is exposed to at least one traumatic event during their lifetime, the utility of this treatment is limited by the logistical problems of treating everyone at risk for developing PTSD after a trauma. To date, there are very few systematic studies on humans that focus on changing the underlying traumatic memory once PTSD has been established.