The primary aim of this study is to assess the safety and efficacy of psilocybin-assisted therapy in the treatment of post-traumatic stress disorder in United States military Veterans.

The objective of this study is to determine the safety and efficacy of psilocybin assisted psychotherapy in the treatment of Veterans with PTSD.

This study will recruit 15 United States Military Veterans, age 21 to 64, primarily from the Columbus and Central Ohio Region who meet the criteria for PTSD. After enrollment and informed consent, participants will receive two separate doses of psilocybin in conjunction with preparatory and post-psilocybin therapy sessions. Each psilocybin session will last approximately 8 hours and will be facilitated by two trained session facilitators. Before the first psilocybin session, participants will meet with one or both of the session facilitators for a total of 6-8 hours of contact time (or up to 4 meetings) before the first psilocybin session day. Two post psilocybin therapy session visits will follow Psilocybin Sessions 1 and 2. Psilocybin Sessions 1 and 2 will occur about two weeks apart. Follow-up visits will occur 1 and 2 weeks and 1, 3, and 6 months after the final psilocybin session, with additional contact hours scheduled as needed. Thus, the intervention and follow-up requires at least 13 visits over a period of about 8-10 months.

In order to be eligible to participate in this study, an individual must meet all of the following criteria:

• A US military Veteran
• 21 to 64 years old
• Have at least a high-school level of education or equivalent.
• Have a current DSM-5 diagnosis of Post-Traumatic Stress Disorder
• Have a CAPS-5 total severity score of ≥35 at baseline
• No antidepressant medications prior to enrollment
• Be judged by study team clinicians to be at low risk for suicidality
• Be medically stable
• Have limited lifetime use of hallucinogens

General medical exclusion criteria:

• Women who are pregnant
• Cardiovascular conditions
• Epilepsy with history of seizures
• Insulin-dependent diabetes
• Currently taking psychoactive prescription medication
• Currently taking on a regular (e.g., daily) basis any medications having a primary centrally-acting serotonergic effect, including Monoamine oxidase inhibitors..

Psychiatric Exclusion Criteria:

• Current or past history of schizophrenia or other psychotic disorders or Bipolar I or II Disorder
• Current or history within one year of a moderate or severe alcohol, tobacco, or other drug use disorder
• Have a first or second-degree relative with schizophrenia spectrum or other psychotic disorders or Bipolar I or II Disorder
• Has a psychiatric condition which precludes the establishment of therapeutic rapport
• History of a medically significant suicide attempt
• Current antidepressant use