 The purpose of this study is to investigate a new use for a medication called levodopa L-DOPA. L-DOPA has been approved for use in Parkinson s disease, but not for Posttraumatic Stress Disorder PTSD. L-DOPA is thought to enhance certain cognitive abilities that the investigators believe may be affected among women with PTSD. It is hypothesized that L-DOPA may enhance fear extinction learning to a conditioned fear stimulus. If this is true, L-DOPA may improve outcomes for those undergoing certain types of therapy for PTSD, though that aim is beyond the scope of this project. Additionally, the investigators are testing whether an individuals genetic profile affects how well L-DOPA works to enhance cognitive abilities. 