Ketamine and Prolonged Exposure in PTSD

Inclusion Criteria: 1. Diagnosis of chronic (minimum of three months) PTSD (Clinician-Administered PTSD Scale for DSM-5 -CAPS-5 score\>33). 2. Voluntarily eligible to participate in PE. 3. Severity of PTSD symptoms defined by PCL-5\>33. 4. Psychotropic medications on stable doses (no dosing adjustments/changes for ≥4 weeks; ≥6 weeks for fluoxetine) prior to prior to beginning of the study. Exclusion Criteria: 1. Unwillingness/unable to sign informed consent. 2. Previous or current participation in trauma-exposed therapy and/or ketamine treatment. 3. Evidence of mental retardation, pervasive developmental disorder and/or moderate/severe cognitive impairment (MMSE scores ≤27). 4. Any unstable medical or non-psychiatric CNS condition. 5. Lifetime history of psychosis-related disorder, bipolar disorder I or II disorder, or any condition other than PTSD judged to be the primary presenting psychiatric diagnosis. 6. Moderate to severe traumatic brain injury (mental status change or loss of consciousness\>30 min; Glasgow Coma Scale \<13; post-traumatic amnesia\>24hours; visible lesion on CT/MRI brain scan). 7. Active alcohol/illicit substance use disorder within 6 months of initial assessment; presence of illicit drugs by positive urine toxicology. 8. For women: pregnancy (confirmed by lab test), initiation of female hormonal treatments within 3 months of screening, or inability/ unwillingness to use a medically accepted contraceptive method during the study. 9. Imminent risk of suicidal/homicidal ideation and/or behavior with intent and/or plan