Morphine prevents the development of stress-enhanced fear learning

► We utilize the stress-enhanced fear learning (SEFL) model of PTSD. ► Repeated morphine administration following trauma blocks SEFL ► Single morphine injection given immediately following trauma has no effect on SEFL. ► A single morphine injection given 48-hours after the trauma block SEFL ► Morphine may be an effective preventative therapy for populations at-risk for PTSD.