Eligibility Criteria:
Inclusion Criteria:
* Participant is a male veteran.
* Veteran meets the Diagnostic and Statistical Manual of Mental Disorders, 4th Edition (DSM-IV) diagnostic criteria for chronic PTSD.
* Veteran has a CAPS total score (past month symptom status) greater than or equal to 50 at screening.
* For veterans taking psychotropic medications (i.e., antidepressants, antipsychotics or anxiolytics/sedative-hypnotics), the veteran will be on a stable dose for at least five weeks prior to screening.
* For veterans not taking psychotropic medication, a minimum of five half-lives must elapse prior to screening since the veteran last took any given psychotropic medication.
Exclusion Criteria:
* Veteran recently continued to engage in a maladaptive pattern of alcohol/substance use and/or abuse (as defined in protocol).
* Veteran has used potent CYP3A4 inhibitors (fluconazole, ketoconazole, itraconazole, erythromycin, rifampin) and inducers within five half-lives prior to randomization.
* Veteran is taking simvastatin, lovastatin, fentanyl, pimozide, bupropion, nefazodone, dihydroergotamine, ergotamine, quinidine, sirolimus, tacrolimus, or clarithromycin, cyclosporine, St. John's Wort, diltiazem, verapamil, propranolol, alprazolam, carvedilol or some anticonvulsants (phenytoin, phenobarbital, or carbamazepine) within five half-lives prior to randomization.
* Veteran is taking oral corticosteroids within five half-lives prior to randomization.
* Veteran should be free of a major medical illness and medical condition that contraindicate the administration of mifepristone. These include but are not limited to:
1. Veteran has a history of adrenal insufficiency or a low plasma cortisol level at screening (a.m. level less than 5 mcg/dl or a p.m. level of less than 3 mcg/dl.)
2. Veteran has a history of severe traumatic brain injury, a history of a stroke, or another neurological illness or injury likely to impact cognitive functioning.
3. Veteran has diabetes mellitus, an endocrinopathy, or another major medical illness.
4. Veteran has a history of cardiovascular disease including a history of angina, myocardial infarction or other evidence of coronary artery disease, or congestive heart failure.
5. Veteran has prolonged QTc interval \>450 msec on ECG at screening.
6. Veteran has hypokalemia at screening (defined as potassium level \< 3.5 Milliequivalent Per Liter (mEq/L)).
7. Veteran has a history of hepato-biliary disease or an aspartate transaminase (AST), alanine transaminase (ALT) greater than 2 times the Upper Limit of Normal (ULN).
8. Veteran has a history of renal disease or an estimated glomerular filtration rate (GFR) of \< 60 ml/min.
* Veteran has a lifetime diagnosis of schizophrenia, schizoaffective disorder, or type I bipolar disorder.
* Veteran has a history of attempted suicide within the previous two years or active suicidal ideation within the past month as assessed by the Columbia-Suicide Severity Rating Scare (C-SSRS).
* Veteran is currently receiving specialized trauma-focused psychotherapy, such as prolonged exposure therapy and cognitive processing therapy.
* Veteran is not willing to use effective means of birth control during the study.
* Veteran has a history of allergic reaction to mifepristone.
* Veteran is found to be unsuitable for study participation at the discretion of the site investigator for any reason.