There are limited current treatments available for PTSD, and the only FDA-approved medications are SSRIs, which were empirically found to be somewhat helpful. Losartan provides a potentially important and exciting development in that it is readily available, safe, inexpensive (available as a generic drug), and has a neurobiological mechanism based on recent exciting discoveries, as outlined below. This proposal is designed to test, in a multisite RCT, this novel, mechanistically-determined, safe and well-tolerated, potentially powerful treatment for PTSD symptoms.