Effects of Repeated Psilocybin Dosing in OCD

Aim 1: To examine the effects of two doses of psilocybin on OCD symptoms among participants in the immediate treatment condition, compared to participants in the waitlist control/delayed treatment condition. The investigators hypothesize that participants in the immediate treatment group will report statistically significantly greater symptom improvement from baseline 4 days post-second dose, compared to participants in the waitlist control/delayed treatment group at the same interval during their waitlist phase.

Aim 2: To examine the effects of two doses of psilocybin on OCD symptoms, compared to one dose. The investigators hypothesize that two doses of oral psilocybin will reduce OCD symptoms to a statistically significantly greater extent than one dose.

This study aims to investigate the effects of repeated dosing of oral psilocybin on OCD symptomatology and assess psychological mechanisms that may mediate psilocybin's therapeutic effects on OCD. This study will employ a randomized, waitlist-controlled design with blinded independent ratings, with participants randomized to receive either immediate treatment (two doses oral psilocybin separated by one week) or delayed treatment (7 weeks post-randomization). An adaptive dose selection strategy will be implemented, with the first dose being standardized at 25 mg of psilocybin, and the second dose being either the same or a higher dosage (i.e., 30 mg) on the basis of a clinically significant response from baseline or not, respectively, 4 days post-first dose.

This study is conducted entirely on an outpatient basis with the possibility of remote/virtual follow-up visits after each dosing session. The dosing sessions last the entire day, and participants will be medically cleared prior to being permitted to return home with assistance (e.g., driven by a family member or friend, or ride share).

Inclusion criteria

• Primary DSM-5 diagnosis of OCD, with Y-BOCS-II score of 26 or greater at screening
• Failed at least one medication and/or therapy trial of standard care treatment for OCD
• English fluency
• Agree to sign a medical release for investigators to communicate directly with participants' providers to confirm medication and psychotherapy histories or arrange contingencies in event of crises.
• Agree to provide an adult contact (relative, spouse, close friend or other caregiver) who is willing and able to be reached by the PI and/or study personnel in the event of an emergency, and who can provide transportation for study visits and independently comment on any changes in the participant's mood or behavior after each administration of psilocybin.
• Agree to commit to all study procedures.
• Ability to orally ingest pills for psilocybin dosing visits.
• Agree to adhere to lifestyle and medication modifications.
• Must not be on psychotropic medications for OCD or comorbid psychiatric conditions for at least 8 weeks at the time of randomization, and agree to refrain from taking or starting any psychiatric medications until after 4 weeks post-second dose.
• Must not be in current psychotherapy (CBT or ERP) and must not start new course of psychotherapy (CBT or ERP) for OCD or comorbid psychiatric conditions until after 4 weeks post-second dose.
• If participant is of childbearing potential, must have a negative pregnancy test at study entry and prior to each dosing session.
• If participant is of childbearing potential, agree to use adequate birth control and not attempt to become pregnant during study up to 4 weeks post-second dose.

Exclusion criteria

• Personal or immediate (first-degree relative) family history of formally diagnosed schizophrenia or other psychotic disorders, or bipolar I/II disorder
• Lack of knowledge about biological families' medical history, due to adoption or other circumstance
• Active suicidal intent or suicidal or non-suicidal self-injurious behaviors
• Unremitted Tourette syndrome
• Lifetime diagnosis of autism spectrum disorder
• Current substance use disorder (except for mild alcohol use disorder)
• Any neurological condition, including history of seizure(s) or chronic/severe headaches
• Any history of head injury with loss of consciousness for more than 30 min
• Any use of classic psychedelic substances within the prior 12 months
• Unwillingness to abstain from use of classic psychedelics outside of the study up to 4 weeks post-second dose.
• Use of tobacco products or a THC-containing product more than 2 times per week on average over the past 30 days at screening.
• Unwilingness or inability to abstain from use of tobacco or THC-containing products from 1 week prior to randomization up to 4 weeks post-second dose.
• Positive urine drug test for any prohibited substance at screening or days of dosing, or positive breathalyzer test for alcohol on days of dosing
• Unwillingness or inability to abstain from alcohol use at least 24 hours prior to the days of dosing, up to 24 hours after each dosing day (or corresponding intervals for waitlist group).
• Any medical conditions that may render study procedures unsafe, including hypertension, history of cardiovascular disease, moderate-to-severe hepatic or renal impairment, diabetes, and hypo- or hyperthyroidism.