This study aims to first identify the optimal estradiol (E2) dose that best engages the fear extinction network among healthy women using oral contraceptives. The second objective is to then evaluate the impact of this optimal E2 dose, when administered in conjunction with 5 sessions of Prolonged Exposure therapy, on the functional activity of the fear extinction network of women with clinically significant posttraumatic stress disorder symptoms. This approach will elucidate the neural mechanisms underlying effective exposure treatment for these symptoms, and will document how estradiol could be used as adjunct to enhance the outcome of extinction-based therapies.