The investigators propose to conduct a randomized double-blind, parallel-group, placebo-controlled trial of mifepristone in veterans with military-related posttraumatic stress disorder (PTSD). This study will examine the clinical, neuropsychological, and neuroendocrine effects of short-term treatment of mifepristone (600 mg/day for one week) to determine if this treatment is efficacious in improving PTSD symptoms, cognitive functioning, or other related clinical measures. Additionally, the investigators will observe whether baseline neuroendocrine activity, or other clinical or neuropsychological factors predict the response to mifepristone, and whether mifepristone-induced changes in neuroendocrine activity are associated with treatment outcome.

Inclusion Criteria:

• Subject is a male U.S. veteran
• Subject was exposed to combat or another criterion A traumatic event during military service
• Subject meets diagnostic criteria for chronic PTSD

Exclusion Criteria:

• Veteran has a history of adrenal insufficiency or a plasma cortisol level less than 5 mcg/dl at screening
• Veteran has a moderate-severe traumatic brain injury, a history of a stroke, or another neurological illness or injury likely to impact cognitive functioning
• Veteran has diabetes mellitus, an endocrinopathy, or another major medical illness.
• Veteran is taking oral corticosteroids
• Veteran has a lifetime diagnosis of schizophrenia, schizoaffective disorder, or bipolar disorder
• Veteran is currently suicidal or otherwise is in need of urgent clinical care
• Veteran is currently receiving specialized trauma-focused psychotherapy (i.e., prolonged exposure, cognitive processing therapy or eye movement and desensitization reprocessing).
• Veteran is not willing to use effective means of birth control during the study or for 90 days after taking study medication
• Veteran has history of allergic reaction to mifepristone