Combining Esketamine and Prolonged Exposure Treatment for PTSD (Post Traumatic Stress Disorder)

Inclusion Criteria: 1. Individual between the ages of 18-65 years old (Young adults \[18 to 24 years old\] must not be taking an antidepressant). 2. PTSD diagnosis as assessed by Clinician-Administered Posttraumatic Stress Scale (CAPS-5) 3. Able to speak and read English (due to standardization of outcome measures) 4. On stable doses of current medications for at least 4 weeks 5. Weigh between 50-100 kg (110-220 pounds). Exclusion Criteria: 1. Young adults (18-24) currently taking any antidepressant. 2. Lifetime history of psychotic disorder or history of significant psychotic symptoms. 3. Lifetime history of manic episode. 4. Moderate or greater severity for alcohol or substance use disorder (DSM-5) in the previous six months. 5. A history of ketamine or phencyclidine abuse. 6. Evidence of a traumatic brain injury severe enough to interfere with comprehension and responding to the baseline screening questionnaires. 7. Current suicidal ideation severe enough to warrant immediate attention (as determined by the Depressive Symptoms Index-Suicidality Subscale and corroborated by a clinical risk assessment by a credentialed provider) 8. Other psychiatric disorders severe enough to warrant designation as the primary disorder as determined by clinician judgment. 9. Current use (with past 4 weeks) of any prohibited concomitant medications 10. Benzodiazepines, other medications, sedatives, acute alcohol use, or recreational drug use that would put patients at risk in the judgment of clinical providers). 11. Planned use of ketamine (i.e., for pain control) or participation in another trauma-focused psychotherapy during the time of the study. 12. Uncontrolled hypertension or tachycardia 13. A history of sensitivity or adverse reaction to ketamine or its excipients 14. An unstable medical, cardiovascular, pulmonary, or neurological condition that the investigator considers a contraindication to ketamine administration 15. Aneurysmal vascular disease (including thoracic and abdominal aorta, intracranial and peripheral arterial vessels) or arteriovenous malformation. 16. Intracerebral hemorrhage. 17. Pregnancy or breastfeeding; women of childbearing potential unwilling to utilize reliable methods of contraception 18. History of nasal surgery or nasal obstructions experienced as an adult. 19. Inability to arrange for assisted transportation on ketamine treatment days due to recommendation that patient not drive for the remainder of the day following a ketamine treatment.