Inclusion Criteria:  1. DSM-5 diagnosis of OCD established by a trained clinician interview and confirmed by Mini International Neuropsychiatric Interview MINI (edition 7).  2. Y-BOCS score of 16 or greater at evaluation 3. Treatment resistant- Patients; must have failed at least one medication and/or therapy trial of standard care treatment for OCD.  4. Age: 18 Years to 65 Years 5. Has been off selective serotonin inhibitors for five half-lives of the drug plus 2 weeks.  6. Must avoid starting new psychotherapy or psychiatric (medical) treatment during the study, without consulting the study team.  7. Are willing to refrain from taking any psychiatric medications or recreational drugs during the study period.  8. Must have a negative pregnancy test at study entry and prior to each experiential/ psychedelic session, if able to bear children, and must agree to use adequate birth control.  9. Must be willing to sign a medical release form for the investigators to communicate directly with their therapist and doctors to confirm a medication and/or medical history. This is decided on a case by case basis upon the discretion of the PI.  10. Must provide a contact (relative, spouse, close friend, or other caregiver) who is willing and able to be reached by the Clinical Investigators in the event of a participant becoming suicidal or any another relevant reason.  11. Are willing to commit to medication dosing, experiential/ psychedelic sessions, psychotherapy and follow-up sessions and to complete the full evaluation.  Exclusion Criteria:  1. Personal or immediate family history of schizophrenia, bipolar affective disorder, delusion disorder, paranoid disorder, or schizoaffective disorder.  2. Current (or last 12-month) substance abuse disorder. 3. Unstable neurological or medical condition. 4. Active suicidal intent or last 12-month suicidal attempt. 5. A history of violence, self-harm, or harm to another. 6. Any unstable medical condition that may render study procedures unsafe. 7. Positive urine pregnancy test at the time of screening. 8. Any use of psychedelic drugs within the prior 12 months. 9. Lack of ability to sign Informed consent. Exclusion Criteria during the study  Any unusual reaction to any of the study procedures. A participant's request to stop his/ her participation in the study. Positive pregnancy test at any stage prior to the last psychedelic session