Psilocybin for Treatment of Obsessive Compulsive Disorder

Inclusion Criteria: * Have moderate to severe OCD (DSM-5) after diagnostic interview using the Structured Clinical Interview for DSM-5 Research Version (SCID-R). * Failed at least one adequate attempted routine care treatment. * Considered safe for independent living Exclusion Criteria: * Concurrent psychosis, active substance use disorder, or a personal history of psychosis. * Medical illness based on physical examination and routine blood testing that may complicate cardiovascular safety or drug metabolism or excretion, such as uncontrolled hypertension, severe cardiac disease, or kidney or liver failure. * Unstable Chronic Obstructive Pulmonary Disease (COPD) or severe sleep apnea * Psychiatric comorbidity that may represent an acute risk to their own or others' safety. * Subjects may not be using antidepressant medication for OCD for at least two weeks before receiving study drug, and they cannot require any sedative, narcotic, or neuroleptic medications on a regular basis. Any of these medications they have taken should have been stopped long enough in the past to allow for their elimination and safe withdrawal prior to starting administration of the study drug. The specific time required will be dependent on the medication the patient was previously receiving. * Women who are pregnant, breastfeeding, or unwilling/unable to practice medically acceptable birth control during the study. * Allergy to lorazepam.