Ketamine as a Treatment for Post-Traumatic Stress Disorder (PTSD)

Inclusion Criteria: * Men or women, 18-65 years of age; * Participants must have a level of understanding sufficient to agree to all tests and examinations required by the protocol and must sign a written informed consent document; * Participants must fulfill DSM-5 criteria for current civilian or combat-related PTSD * Women must be using a medically accepted reliable means of contraception (if using an oral contraceptive medication, they must also be using a barrier contraceptive) or not be of childbearing potential (i.e., surgically sterile, postmenopausal for at least one year); * Women of childbearing potential must have a negative pregnancy test at screening and prior to each intravenous infusion; * Participants must be able to identify a family member, physician, or friend (i.e. someone who knows them well) who will participate in a Treatment Contract (and e.g. contact the study physician on their behalf in case manic symptoms or suicidal thoughts develop). Exclusion criteria: * Women who plan to become pregnant, are pregnant or are breast-feeding * Serious, unstable medical illnesses such as hepatic, renal, gastroenterologic, respiratory, cardiovascular, endocrinologic, neurologic, immunologic, or hematologic disease, including gastro-esophageal reflux disease, obstructive sleep apnea, history of difficulty with airway management during previous anesthetics, ischemic heart disease and uncontrolled hypertension, and history of severe head injury; * Clinically significant abnormal findings of laboratory parameters, physical examination, or ECG; * Renal impairment, as reflected by a BUN \>20 mg/dL, and/or creatinin clearance of \>1.3 mg/dL; * Thyroid impairment, as reflected by TSH\> 4.2 mU/L Patients with uncorrected hypothyroidism or hyperthyroidism; * Hormonal treatment (e.g., estrogen) started in the 3 months prior to the first infusion day; * Use of evidence-based individual psychotherapy (such as prolonged exposure) during the study; * History of autism, mental retardation, pervasive developmental disorders, or Tourette's syndrome; History of one or more seizures without a clear and resolved etiology; * History of (hypo)mania; * Past or current presence of psychotic symptoms, or diagnosis of a lifetime psychotic disorder including schizophrenia or schizoaffective disorder; * Drug or alcohol abuse or dependence within the preceding 3 months * Previous recreational use of ketamine or PCP; * Current diagnosis of bulimia nervosa or anorexia nervosa; * Diagnosis of schizotypal or antisocial personality disorder * Patients judged clinically to be at serious and imminent suicidal or homicidal risk. * A blood pressure of one reading over 160/90 or two separate readings over 140/90 at screen or baseline visits * Patients who report current treatment with a benzodiazepine, an opioid medication, or a mood stabilizer (such as valproic acid or lithium) within 2 weeks prior to randomization