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

Inclusion Criteria: * Men or women, 21-55 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-IV criteria for current civilian or combat-related PTSD, based on clinical assessment by a study psychiatrist and on the CAPS (score must be at least 50 at screening and prior to each infusion - this is done to ensure at least moderate severity and to safeguard against high placebo response rates); additionally, clinicians will use clinical judgment to assess if patients are symptomatic enough to receive each infusion * 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 pre-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 (because the medical risk of using ketamine during pregnancy and breast-feeding is unknown); * 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; * 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) and other non-pharmacological treatments during the study; * Histories 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 (given that this might otherwise contribute to their symptoms, however, a rather narrow time period was chosen such as to allow participation by individuals with a history of substance abuse or dependence problems that could be secondary to their PTSD, and to more closely approximate patients seen in real-world settings); * Previous recreational use of ketamine or PCP; * Current diagnosis of bulimia nervosa or anorexia nervosa; * Diagnosis of schizotypal or antisocial personality disorder (since these are known to reduce the possibility of study completion; other Axis II diagnoses will be allowed); * 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.