The principal investigator for this study plans to build upon the psilocybin-assisted therapy intervention used in prior completed trials to conduct an open-label trial of two psilocybin administration sessions combined with psychotherapy to investigate the safety, tolerability, and clinical efficacy of psilocybin-assisted therapy for the treatment of PTSD in US Veterans.

Inclusion Criteria:

• Be a United States Military Veteran
• Have at least a high-school level of education or equivalent (e.g. GED).
• Have a current DSM-5 diagnosis of Post-traumatic Stress Disorder
• Have a CAPS-5 total severity score of ≥23 at baseline
• SSRIs will be allowable so long as participants are on a stable regimen for a period of 3 months.
• Concurrent psychotherapy is allowed if the type and frequency of the therapy has been stable for at least 2 months prior to screening and is expected to remain stable during participation in the study.
• Be medically stable as determined by screening for medical problems via a personal interview, a medical questionnaire, a physical examination, an electrocardiogram (ECG), and routine medical blood and urinalysis laboratory tests
• No use of hallucinogens in the past 3 months and no history of regular or frequent use of hallucinogens

Exclusion Criteria:

• General medical exclusion criteria:

  • Individuals who are pregnant or nursing; individuals who are of child-bearing potential and sexually active who are not practicing a highly effective means of birth control
  • Individuals with partners of childbearing potential who are sexually active and not practicing a highly effective means of contraception
  • Cardiovascular conditions: coronary artery disease, stroke, angina, uncontrolled hypertension, a clinically significant ECG abnormality (e.g., atrial fibrilation), prolonged QTc interval (i.e., QTc > 450 msec), artificial heart valve, or TIA in the past year • Systolic blood pressure (SBP) > 139 mm HG; diastolic blood pressure (DBP) > 89 mm HG; heart rate (HR) > 90 bpm.
  • Epilepsy with history of seizures
  • Insulin-dependent diabetes; if taking oral hypoglycemic agent, then no history of symptoms of hypoglycemia

• Psychiatric Exclusion Criteria:

  • Current or past history of meeting DSM-5 criteria for schizophrenia spectrum or other psychotic disorders (except substance/medication-induced or due to another medical condition), or Bipolar I or II Disorder
  • Current or history within six months of meeting DSM-5 criteria for a moderate or severe alcohol, tobacco, caffeine, or other drug use disorder; if a regular smoker, they must agree to use a nicotine patch on the day of dosing as smoking will not be allowed on these sessions
  • Have a first degree relative with schizophrenia spectrum or other psychotic disorders including substance/medication-induced or due to another medical condition
  • Risk for acute suicidality as determined by clinician judgment (C-SSRS)
  • Has a psychiatric condition which precludes the establishment of therapeutic rapport as evidenced by long-term patterns of unstable relationships, history of significant stress-related paranoia, and identity disturbances
  • History of a medically significant suicide attempt
  • Current MAOI antidepressant use