A Phase 1 interventional study of Psilocybin (0.25mg/kg) and Niacin (250mg) in Obsessive-Compulsive Disorder, sponsored by Yale University. Completed at 1 site in United States. Open to participants aged 21 Years to 65 Years. Per ClinicalTrials.gov, last updated 2026-10-16.
Sponsored by Yale University · Phase 1, Interventional, and Treatment
This study aims to investigate the effects of oral psilocybin on OCD symptomatology and provide the first evidence of the neural mechanism that may mediate psilocybin's purported therapeutic effects on OCD.
Aim 1: To investigate the effects of psilocybin on OCD symptomatology. OCD symptom severity will be assessed before treatment and 24 and 48 hours after treatment, one week after treatment, two weeks, one month, and three months after treatment. Hypothesis: We hypothesize that 0.25mg/kg of psilocybin will lead to greater symptom improvement than niacin (as the active-placebo-control agent) at the primary endpoint of 48 hours post-dosing and at all other assessment points.
Aim 2: To explore the relationship between the psilocybin-induced brain connectivity changes and symptom change in OCD. Resting-state brain connectivity will be assessed before and 48 hours after treatment. Hypothesis: We hypothesize that (i) psilocybin will normalize abnormal fronto-striatal functional connectivity in patients with OCD; and (ii) normalization of these abnormalities will correlate with improvement in symptomatology after psilocybin treatment.
This study will pilot a single-center, randomized, active-placebo-controlled, double-blind design to examine the clinical and neural effects on OCD, of either 0.25mg/kg of psilocybin or active placebo-control agent (niacin 250mg), given along with non-drug preparatory and follow-up support appointments to 30 study participants. The duration of the randomized study phase is from consent until two weeks after drug administration. Participants will be followed for 12 weeks (3 months) post-study drug administration.
Eligible participants will be admitted as an inpatient for at least 3 nights / 4 days surrounding the initial drug administration (or more, at the option of the subject and the investigator). Participants will be randomized into active medication and active-placebo-control groups, and will be blinded as to their study condition. This admission 2 nights prior to the drug administration will allow the participant to adjust to sleeping on the unit and allow them to settle in to the research unit routine. A return for an fMRI scan (48 hours after the administration session) will be scheduled. The participants who received active-placebo-control will be offered the option to receive open-label psilocybin.
635 studies on the registry are indexed under Obsessive-Compulsive Disorder; 166 are open to participants now.
This study's enrollment of 28 is below the median of 45 across 520 interventional studies indexed under Obsessive-Compulsive Disorder.
Browse Obsessive-Compulsive Disorder studies →Yale University is the lead sponsor of 1,770 studies on the registry; 294 are open to participants now.
Of its 221 completed or terminated interventional studies of FDA-regulated products, 129 (58%) have results posted.
Counted across the registry records on this site, refreshed daily.
Go through the criteria one by one — yes, no or not sure — and take the list to your doctor or the study team. Kept in this browser only.
Exclusion Criteria:
Underlined terms in the criteria open these too. Explained by clinicaltrials.gg, not part of the registry record. The study team decides who can take part.
The American Psychiatric Association’s manual of mental health diagnoses. DSM-5 (2013, revised as DSM-5-TR in 2022) replaced DSM-IV, and some studies still name the older edition. “Meets DSM criteria for …” means diagnosed by that edition’s diagnostic criteria, usually by a clinician in an interview.
Before you join, the study team explains what taking part involves — its purpose, what happens, the risks and possible benefits — and answers your questions, so you can decide freely. Consent is usually recorded on a form (the informed consent form, ICF) signed by you or, where the law allows, by someone legally authorised to decide for you.
You can keep asking questions during the study, you are told of new information that matters, and you can choose to leave at any time.
Able to become pregnant: from the first period until menopause, unless permanently unable to through surgery (removal of the womb, or of both ovaries or both fallopian tubes).
Criteria for people of childbearing potential usually ask for a negative pregnancy test and for contraception during the study and for a time after it.
Ways of preventing pregnancy. “Highly effective” methods fail less than 1% of the time a year when used correctly — for example an IUD or an implant.
Criteria usually say which methods count and how long to keep using them after the last dose, sometimes for male participants too. Some studies accept a partner’s vasectomy if it was confirmed successful and that person is the participant’s only sexual partner.
A reason a treatment, test or procedure should not be given to a particular person, such as an allergy, another illness or a medicine they take.
DSM diagnostic criteria
The American Psychiatric Association’s manual of mental health diagnoses. DSM-5 (2013, revised as DSM-5-TR in 2022) replaced DSM-IV, and some studies still name the older edition. “Meets DSM criteria for …” means diagnosed by that edition’s diagnostic criteria, usually by a clinician in an interview.
Explained by clinicaltrials.gg, not part of the registry record. The study team decides who can take part.
Informed consent
Before you join, the study team explains what taking part involves — its purpose, what happens, the risks and possible benefits — and answers your questions, so you can decide freely. Consent is usually recorded on a form (the informed consent form, ICF) signed by you or, where the law allows, by someone legally authorised to decide for you.
You can keep asking questions during the study, you are told of new information that matters, and you can choose to leave at any time.
Explained by clinicaltrials.gg, not part of the registry record. The study team decides who can take part.
Childbearing potential
Able to become pregnant: from the first period until menopause, unless permanently unable to through surgery (removal of the womb, or of both ovaries or both fallopian tubes).
Criteria for people of childbearing potential usually ask for a negative pregnancy test and for contraception during the study and for a time after it.
Explained by clinicaltrials.gg, not part of the registry record. The study team decides who can take part.
Contraception
Ways of preventing pregnancy. “Highly effective” methods fail less than 1% of the time a year when used correctly — for example an IUD or an implant.
Criteria usually say which methods count and how long to keep using them after the last dose, sometimes for male participants too. Some studies accept a partner’s vasectomy if it was confirmed successful and that person is the participant’s only sexual partner.
Explained by clinicaltrials.gg, not part of the registry record. The study team decides who can take part.
Contraindication
A reason a treatment, test or procedure should not be given to a particular person, such as an allergy, another illness or a medicine they take.
Explained by clinicaltrials.gg, not part of the registry record. The study team decides who can take part.
Psilocybin (0.25mg/kg)
Drug: Psilocybin (0.25mg/kg)
Niacin (250mg)
Drug: Niacin (250mg)
Drug page: Psilocybin
Psilocybin is a naturally occurring hallucinogenic ingredient found in some varieties of mushrooms that can be produced synthetically. It is considered to be a serotonergic psychedelic.
Also known as: "Magic Mushrooms"
A medication used to treat high cholesterol, triglyceride levels, and niacin deficiency.
Also known as: Nicotinic acid
Changes in Severity of OCD Symptoms, Which Will be Measured by The Yale-Brown Obsessive-Compulsive Scale (Y-BOCS). The Primary Outcome Measure Will be Collected at Baseline and 48 Hours, Assessing Change From Baseline at 48 Hours.
Assesses severity and types of OCD symptoms over the past seven days. Consists of two parts: 1- symptom checklist, 2- symptom severity scale. The most prominent obsessions and compulsions are identified by the checklist and then rated by the symptom severity scale. The symptom severity scale consists of 11 items (3 items are not included in the total score) and uses a 0 to 4 severity scale. Total Y-BOCS scores range from 0 to 40, with higher scores indicating greater severity of OCD symptoms.
Time frame: Baseline, weeks: 1, 2, 4, 12 post-drug
Changes in Severity of OCD Symptoms, Measured by Acute Yale-Brown Obsessive-Compulsive Scale (A-YBOCS)
A clinician-administered measure of specific participant OCD symptoms over prior 24 hours. The most prominent obsessions and compulsions that were previously identified by the checklist are rated by the symptom severity scale. The symptom severity scale consists of 11 items (3 items are not included in the total score) and uses a 0 to 4 severity scale. Total A-YBOCS scores range from 0 to 40, with higher scores indicating greater severity of OCD symptoms. Data presented here is the mean change from baseline to 48 hours post-drug.
Time frame: Day 1 (drug treatment), 24 hours post-drug, 48 hours post-drug
Changes in Severity of OCD Symptoms, Measured by Visual Analog Scale (VAS) for OCD Symptoms
A self-report measure of severity of and distress related to OCD symptoms over the past 24 hours. Consists of 5 items assessing compulsive urges, obsessions, anxiety, mood, and discomfort, each on a 0-100 VAS, with higher scores on each item indicating greater severity.
Time frame: 24 hours post-drug, 48 hours post-drug
Changes in Suicidality, Measured by the Columbia-Suicide Severity Rating Scale (C-SSRS) Since Last Visit Version
A clinician-administered measure of suicidality since the last visit. Consists of 5 items assessing suicidal ideation and 6 items assessing suicidal and non-suicidal self-injurious behaviors. Higher scores on either scale indicate more severe suicidal ideation and suicidal or non-suicidal behaviors since the last study visit. Data presented here is the number of participants with new suicidal ideation cases, number of participants with Suicide attempts and number of participants with completed Suicides
Time frame: Up to 12 weeks post-drug
Changes in Functional Impairment, Which Will be Measured by The Sheehan Disability Scale (SDS).
Assesses functional impairment in three inter-related domains; work/school, social and family life. Impairment of each domain is rated from 0 (not at all) to 10 (extremely). The 3 items are summed into a single dimensional measure of global functional impairment that rages from 0 (unimpaired) to 30 (highly impaired). Mean difference presented here.
Time frame: Baseline & 12 weeks post-drug
Changes in Depression Symptoms, Which Will be Measured by The Montgomery-Asberg Depression Scale (MADRS).
Assesses depression symptoms. Consists of 10 items and uses a 0 to 6 severity scale. Total scores range from 0 to 60, with higher scores indicating more severe depression.
Time frame: Baseline, 48 hours post-drug, weeks: 1, 2 post-drug
Changes in Connection to Nature, Which Will be Measured by The Nature Relatedness Scale (NRS).
Assesses the affective, cognitive, and experiential aspects of individuals' connection to nature. Consists of 21 items which are rated on a 7-point Likert scale. The total score is calculated by averaging all 21 items after the appropriate items are reversed scored. Higher score indicate a greater connection with nature.
Time frame: Baseline & 2 weeks post-drug
Changes in Opinion Towards Pro-environmental Behavior, Which Will be Measured by The Pro-Environmental Behavior Scale (PEBS).
Assesses opinions towards the importance of pro-environmental behaviors. Consists of 17 items that are rated from 1(not at all important) to 7 (extremely important). Higher total scores indicate a greater level of importance of pro-environmental behaviors.
Time frame: Baseline & 2 weeks post-drug
Changes in Anthropomorphism, Which Will be Measured by The Individual Differences in Anthropomorphism Questionnaire (IDAQ).
Assesses individual differences in anthropomorphism. Consists of 15 items which are rated by a 10-point Likert scale. Higher total scores indicate a higher level of anthropomorphism.
Time frame: Baseline & 2 weeks post-drug
Changes in Beliefs of Mind-body Dualism, Which Will be Measured by The Mind-Body Dualism Scale (MBDS).
Assesses beliefs of mind-body dualism. Consists of 11 items that are rated on a 7-point Likert scale. The total score is calculated after the appropriate items are reversed scored. Higher scores indicate a greater belief in mind-body dualism.
Time frame: Baseline & 2 weeks post-drug
Change in Interpersonal Connectedness, Which Will be Measured by The Inclusion of Others in Self Scale (IOS).
Measures perceived interpersonal connectedness. A single-item, pictorial measure of closeness. Images range from the self and other as completely separate to the self and other almost completely overlapping.
Time frame: Baseline & 2 weeks post-drug
Change in Moral Relativism and Idealism, Which Will be Measured by The Ethical Positions Questionnaire (EPQ).
Assesses moral relativism and idealism. Consists of 20 items that are rated using a 9-point Likert scale (completely disagree to completely agree). Idealism scores are calculated by summing responses from items 1 to 10. Relativism scores are calculated by summing responses from items 11 to 20. Higher scores on items 1 to 10 indicate higher relativism and higher scores on items 11 to 20 higher idealism.
Time frame: Baseline & 2 weeks post-drug
Changes in Alcohol Consumption, Which Will be Measured by The Alcohol Use Disorders Identification Test (AUDIT).
Assesses alcohol consumption, drinking behaviors, and alcohol-related problems. Consists of 10 items. The total score is calculated by summing all items. Higher scores indicate higher alcohol consumption. A score of 8 or more is considered to indicate hazardous or harmful alcohol use.
Time frame: Baseline & 12 weeks post-drug
Changes of the Effects of Psilocybin, Which Will be Measured by The Persisting Effects Questionnaire (PEQ).
Assesses effects of Psilocybin. Consists of 86 items that assess eight categories of possible change in attitudes, mood, social effects, and behavior: 1. positive attitudes about life and/or self (17 items); 2. negative attitudes about life and/or self (17 items); 3. positive mood changes (4 items); 4. negative mood changes (4 items); 5. altruistic/positive social effects (8 items); 6. antisocial/negative social effects (8 items); 7. positive behavior changes (1 item); and 8. negative behavior changes (1item). Each item is rated using a 6-point rating scale from 0 (none, not at all) to 5 (extreme). Higher scores of each subscale indicate greater changes in that category.
Time frame: 2 days post-drug, weeks: 4 & 12 post-drug
Changes in Urgent Care and Emergency Room Use, Which Will be Measured by The Utilization of Facility and Emergent Care (UFEC).
Assesses frequency of urgent care and emergency room use. Consists of 26 items and 7 scales which include: Hypertension, High Cholesterol, Diabetes, Autoimmune, Musculoskeletal, Emergency Room Utilization, Urgent Care Utilization, Hospital Utilization, Facility Based Mental Health Care Utilization, Non-facility Based Mental Health Care Utilization. Items in each scale are scored by comparing follow-up scores to baseline scores. Positive difference indicates improved condition severity (Hypertension, High Cholesterol, Diabetes, Autoimmune, Musculoskeletal). Positive difference indicates reduced Emergency Room Utilization, Urgent Care Utilization, Hospital Utilization, Facility Based Mental Health Care Utilization, Non-facility Based Mental Health Care Utilization.
Time frame: Baseline & 12 weeks post-drug
Changes in Drug-related Problems, Which Will be Measured by The Drug Use Disorders Identification Test (DUDIT).
Assesses drug-related problems. Consists of 11 items. The total score is calculated by summing all items. Drug related problems are indicated with a score of 6 or more for men and a score of 2 or more for women.
Time frame: Baseline & 12 weeks post-drug
Changes in Tobacco Use, Motivation to Quit, and Dependence, Which Will be Measured by The Self-reported Nicotine Use (SRNU).
Assesses tobacco use, motivation to quit, and dependence. Consists of 13 items. The baseline score of each item is compared to the follow-up score to assess changes. Higher scores indicate greater nicotine use.
Time frame: Baseline & 12 weeks post-drug
Changes in Different Dimensions of Emotional Experience, Which Will be Measured by The Positive and Negative Affect Schedule Expanded Form (PANAS-X).
Assesses different dimensions of the emotional experience. This scale consists of 60 words and phrases that describe different feelings and emotions. For each item participants rate to what extent they have felt this way during the past few weeks from 1 (very slightly or not at all) to 5 (extremely). The items are grouped into the following 4 subgroups and subscales; general dimension scales (negative affect, positive affect), basic negative emotion scales (fear, hostility, guilt, sadness), basic positive emotion scales (joviality, self-assurance, attentiveness), other affective states (shyness, fatigue, serenity, surprise). The items pertaining to each subscale are summed with higher scores indicating higher levels of each subscale.
Time frame: Baseline, 2 days post-drug, weeks: 1, 2, 4, 12 post-drug
5-Dimension - Altered States of Consciousness (5D-ASC)
Assesses different mental states induced by the interventions. Consists of 94 items which are rated by placing marks on a horizontal visual analogue scale (100 millimeters in length). The scale ranges from no, not more than usual (on the left) to yes, very much more than usual (on the right). The items are scored by measuring the millimeters from the low end of the scale to the participant's mark (from 0 to 100).
Time frame: Day of drug administration
Changes in Sleep Quality, Which Will be Measured by The Pittsburgh Sleep Quality Index (PSQI).
Assesses sleep quality. Consists of 19 self-rated questions and 5 questions rated by the bed partner or roommate (if one is available). Only self-rated questions are included in the scoring. The 19 self-rated items are combined to form seven "component" scores, each of which has a range of 0-3 points. In all cases, a score of "0" indicates no difficulty, while a score of "3" indicates severe difficulty. The seven component scores are then added to yield one "global" score, with a range of 0-21 points, "0" indicating no difficulty and "21" indicating severe difficulties in all areas.
Time frame: Baseline, 48 hours post-drug, weeks: 4 & 12 post-drug
Changes in Readiness to Change, Which Will be Measured by The University of Rhode Island Change Assessment (URICA).
Assesses readiness to change. Consists of 30 items rated from 1(strongly disagree ) to 5 (strongly agree). Subscales include: Precontemplation, Contemplation, Action, and Maintenance. Subscale scores are calculated by averaging the items in each subscale. The total score is calculated by summing the subscales Contemplation, Action, Maintenance and subtracting Precontemplation. Higher score indicate greater readiness to change.
Time frame: Baseline, 48 hours post-drug, weeks: 4, 8, 12 post-drug
Challenging Experience Questionnaire (CEQ)
Assesses difficult experiences induced by the interventions. Consists of 26 items that are rated from 0 (none; not at all) to 5 (extreme; more than ever before in my life). Participants are asked to rate the degree to which at any time during the previous session they experienced the following phenomena. Items are grouped into the following subscales: fear, grief, physical distress, insanity, isolation, death, and paranoia. Scores of each item are transformed into a percentage of the highest possible score. Subscale scores are calculated by averaging the transformed scores of the items in each subscale. The total score is the average of all the transformed item scores, with higher scores indicating more challenging experiences.
Time frame: Day of drug administration
Changes in Meaning of Life, Which Will be Measured by The Schedule for Meaning in Life Evaluation (SMiLE).
Assesses individual meaning in life. Participants are asked to name up to seven domains that they judge to be important to their individual meaning in life.Then they will rate their current level of satisfaction in each of these domains using a seven-point Likert scale (range, -3 to +3) and rate the importance of each of their chosen areas using a eight-point adjectival scale (range, 0 to 7). Higher total score indicate a greater meaning in life.
Time frame: Baseline, weeks: 1 & 12 post-drug
Changes in Experiential Aspects of Psilocybin, Which Will be Measured by The Mystical Experience Questionnaire (MEQ).
Assesses different experiential aspects of psilocybin. Consists of 44 items which provides scale scores for each of seven domains of mystical experiences: Internal Unity (6 items); External Unity (6 items); Transcendence of Time and Space (8 items); Ineffability and Paradoxicality (5 items); Sense of Sacredness (7 items); Noetic Quality (4 items). Participants are asked to look back on the extended session that they have just experienced and to rate the degree of their experience of the following phenomena. Each item is rated from 0 (none; not at all) to 5 (extreme; more than ever before in my life and stronger than 4). Total scores are expressed as a proportion of the maximum possible score.
Time frame: Day of drug administration, weeks: 2 & 12 post-drug
Changes in Quality of Life, Which Will be Measured by The Quality of Life Enjoyment & Satisfaction Questionnaire (Q-LESQ-SF).
Assesses quality of life and functionality. Consists of 16 items which are rated from 1 (very poor) to 5 (very good). Total score involves summing only the first 14 items to yield a raw total score. The raw total score ranges from 14 to 70. The raw total score is transformed into a percentage, with higher percentages indicating greater quality of life.
Time frame: Baseline, weeks: 2 & 12 post-drug
Changes in Anxiety, Which Will be Measured by State-Trait Anxiety Inventory (STAI).
Measures state and trait anxiety. Consist of 40 items: 20 items measuring S-Anxiey and 20 items measuring T-Anxiety. State Anxiety Scale (S-Anxiety) evaluates the current state of anxiety. The Trait Anxiety Scale (T-Anxiety) evaluates relatively stable aspects of anxiety. The S-Anxiety scale assesses the intensity of current feelings "at this moment" from 1(not at all) to 4 (very much so). The T-Anxiety scale assesses the frequency of feelings "in general" from 1 (almost never) to 4 (almost always). The range of scores for each subtest is 20-80, with higher scores indicating greater anxiety.
Time frame: Baseline, 2 days post-drug, weeks: 1, 2, 4, 12 post-drug
Changes in OCD Dimensions, Which Will be Measured by The Obsessive-Compulsive Trait Core Dimensions Questionnaire (OC-TCDQ).
Measures different OCD dimensions. Consists of 20 items assessing two core dimensions of OCD: harm avoidance (10 items) and incompleteness (10 items). Each item is rated from 0: never applies to me to 4: always applies to me. Higher scores on questions assessing harm avoidance indicates greater levels of harm avoidance. Higher scores on questions assessing incompleteness indicates higher levels of incompleteness.
Time frame: Baseline & 2 weeks post-drug
Changes in OCD Symptoms, Which Will be Measured by The Obsessive-Compulsive Inventory - Revised (OCI-R).
An inventory of OCD symptoms. Consist of 18 items that are rated on a 5-point Likert scale. Total scores range from 0 to 72, with higher scores indicating more severe OCD symptoms.
Time frame: Baseline & 2 weeks post-drug
Changes in Dysfunctional Beliefs, Which Will be Measured by The Obsessive Beliefs Questionnaire (OBQ-44).
Measures dysfunctional beliefs in obsessive-compulsive disorder. Consists of 44 items that are rated on a seven-point Likert scale, ranging from 1 (disagree very much) to 7 (agree very much). It contains three subscales: overestimations of threat and responsibility for harm (RT subscale), importance and control of intrusive thoughts (ICT subscale), and perfectionism and the need for certainty (PC subscale), with higher scores indicating higher levels of each sub-scale.
Time frame: Baseline & 2 weeks post-drug
Changes in Symptom Severity and Treatment Response, Which Will be Measured by The Clinical Global Impressions (CGI).
Assesses symptom severity and treatment response. Consists of 4 items that are rated on a 7-point Likert scale. Symptom severity scores range from 1 (normal) through to 7 (amongst the most severely ill patients). Treatment response scores range from 1 (very much improved) through to 7 (very much worse). Each component is rated separately; this measure does not yield a global score. Higher scores indicate greater symptom severity and lower treatment response.
Time frame: Baseline & 12 weeks post-drug
Changes in Optimism and Pessimism, Which Will be Measured by The Life Orientation Test Revised (LOT-R).
Assesses individual differences in generalized optimism versus pessimism. Consists of 10 items that are rated from 0 (I agree a lot) to 4 (I disagree a lot). Of the 10 items, 3 items measure optimism, 3 items measure pessimism, and 4 items serve as fillers. Total scores are calculated by summing all items for a total ranging from 0 to 24.There are no "cut-offs" for optimism or pessimism; this measure is used as a continuous dimension of variability.
Time frame: Baseline & 12 weeks post-drug
Changes in OCD Symptoms, Which Will be Measured by The Padua Inventory of OCD Symptoms.
Assesses OCD symptoms across five dimensions: (1) obsessional thoughts about harm to oneself or others; (2) obsessional impulses to harm oneself or others; (3) contamination obsessions and washing compulsions; (4) checking compulsions; and (5) dressing/grooming compulsions. Consists of 39 items that are rated from 0 (not at all) to 4 (very much). Items within each domain are summed for subscale scores. All items are summed for a total score with higher scores indicating greater symptom severity.
Time frame: Baseline & 12 weeks post-drug
Changes in Action Identification, Measured by the Behavior Identification Form (BIF)
Assesses individual variation in identification of several motor actions and activities. Comprises 25 items of various motor actions or activities, of which each can be endorsed and interpreted on a binary response scale as either a literal motor action or a meaningful outcome-oriented behavior. Greater number of items responded literally or meaningfully indicate more literal or meaningful, outcome-oriented behaviors, respectively.
Time frame: Baseline & 1 week post-drug
Changes in Reactions to Research Participation, Measured by the Reactions to Research Participation Questionnaire (RRPQ)
Assesses reactions to research participation. Consists of 26 items (each rated from 1-5) assessing various aspects of participation-related reactions, which can be parsed into 5 subscales: perceptions of participation, personal benefits, emotional reactions, perceived drawbacks, and global evaluation. Higher subscale scores indicate greater extent of respective reactions.
Time frame: 48 hours post-drug and 12 weeks post-drug
Changes in Depression Symptoms, Which Will be Measured by the Beck Depression Inventory (BDI).
Assesses depression symptoms. Consists of 21 items and uses a 0 to 3 severity scale. Total scores range from 0 to 63, with higher scores indicating more severe depression.
Time frame: Baseline, 1 day post-drug, weeks: 2 & 12 post-drug
Changes in Brain Connectivity, Which Will be Measured With Functional Magnetic Imaging Resonance (fMRI).
Resting-state brain connectivity will be assessed before and 48 hours after treatment. Neuronal activation induced by OCD-relevant provocative stimuli will be assessed 48 hours after the treatment.
Time frame: Baseline & 48 hours post-drug
| Milestone | Psilocybin | Niacin |
|---|---|---|
| Started | 14 | 14 |
| Completed 48 hour follow up | 13 | 14 |
| Completed 1 week follow up | 13 | 14 |
| Received psilocybin unblinded | 0 | 14 |
| Completed | 12 | 14 |
| Not completed | 2 | 0 |
Assesses severity and types of OCD symptoms over the past seven days. Consists of two parts: 1- symptom checklist, 2- symptom severity scale. The most prominent obsessions and compulsions are identified by the checklist and then rated by the symptom severity scale. The symptom severity scale consists of 11 items (3 items are not included in the total score) and uses a 0 to 4 severity scale. Total Y-BOCS scores range from 0 to 40, with higher scores indicating greater severity of OCD symptoms.
| score on a scale | Psilocybin | Niacin |
|---|---|---|
| Baseline | 26.36 ± 4.634 | 27.21 ± 3.309 |
| Week 1 | 14.62 ± 8.461 | 25.36 ± 5.048 |
| Week 2 | 16.17 ± 8.089 | — |
| Week 4 | 15.69 ± 9.214 | — |
| Week 8 | 12.75 ± 8.802 | — |
| Week 12 | 15.17 ± 10.373 | — |
A clinician-administered measure of specific participant OCD symptoms over prior 24 hours. The most prominent obsessions and compulsions that were previously identified by the checklist are rated by the symptom severity scale. The symptom severity scale consists of 11 items (3 items are not included in the total score) and uses a 0 to 4 severity scale. Total A-YBOCS scores range from 0 to 40, with higher scores indicating greater severity of OCD symptoms. Data presented here is the mean change from baseline to 48 hours post-drug.
| score on a scale | Psilocybin | Niacin |
|---|---|---|
| Baseline | 24.07 ± 6.019 | 24.29 ± 4.811 |
| 24 hours post-drug | 16.43 ± 7.823 | 23.14 ± 3.634 |
| 48 hours post-drug | 14.31 ± 8.833 | 24.36 ± 3.954 |
A self-report measure of severity of and distress related to OCD symptoms over the past 24 hours. Consists of 5 items assessing compulsive urges, obsessions, anxiety, mood, and discomfort, each on a 0-100 VAS, with higher scores on each item indicating greater severity.
| units on a scale | Psilocybin | Niacin |
|---|---|---|
| 24 hours post-drug- Compulsions | 32.57 ± 18.90 | 41.08 ± 25.90 |
| 24 hours post-drug- Obsessions | 35.57 ± 22.76 | 46.69 ± 26.87 |
| 24 hours post-drug- Anxiety | 28.07 ± 23.88 | 37.46 ± 18.80 |
| 24 hours post-drug- Mood | 55.50 ± 19.19 | 49.00 ± 14.05 |
| 24 hours post-drug- Discomfort | 30.64 ± 25.30 | 36.62 ± 18.62 |
| 48 hours post-drug- Compulsions | 29.46 ± 20.21 | 43.17 ± 29.15 |
| 48 hours post-drug- Obsessions | 29.39 ± 19.88 | 51.17 ± 29.60 |
| 48 hours post-drug- Anxiety | 26.31 ± 20.43 | 51.08 ± 24.24 |
| 48 hours post-drug- Mood | 63.46 ± 17.66 | 49.75 ± 17.10 |
| 48 hours post-drug- Discomfort | 22.23 ± 15.76 | 36.25 ± 27.29 |
A clinician-administered measure of suicidality since the last visit. Consists of 5 items assessing suicidal ideation and 6 items assessing suicidal and non-suicidal self-injurious behaviors. Higher scores on either scale indicate more severe suicidal ideation and suicidal or non-suicidal behaviors since the last study visit. Data presented here is the number of participants with new suicidal ideation cases, number of participants with Suicide attempts and number of participants with completed Suicides
| Participants | Psilocybin | Niacin |
|---|---|---|
| New suicidal ideation cases | 1 | 0 |
| Suicide attempts | 0 | 0 |
| Completed suicides | 0 | 0 |
Assesses functional impairment in three inter-related domains; work/school, social and family life. Impairment of each domain is rated from 0 (not at all) to 10 (extremely). The 3 items are summed into a single dimensional measure of global functional impairment that rages from 0 (unimpaired) to 30 (highly impaired). Mean difference presented here.
| units on a scale | Psilocybin | Niacin |
|---|---|---|
| Changes in Functional Impairment, Which Will be Measured by The Sheehan Disability Scale (SDS). | -8.273 (-12.426 to -4.120) | -0.54 (-3.21 to 2.13) |
Assesses depression symptoms. Consists of 10 items and uses a 0 to 6 severity scale. Total scores range from 0 to 60, with higher scores indicating more severe depression.
| score on a scale | Psilocybin | Niacin |
|---|---|---|
| Baseline | 15 ± 9.938 | 13.57 ± 8.662 |
| 48 hours post-drug | 13.23 ± 7.143 | 12.21 ± 7.17 |
| Week 1 | 7.08 ± 5.965 | 11.43 ± 7.491 |
| Week 2 | 5.54 ± 7.557 | 13 ± 8.385 |
Assesses the affective, cognitive, and experiential aspects of individuals' connection to nature. Consists of 21 items which are rated on a 7-point Likert scale. The total score is calculated by averaging all 21 items after the appropriate items are reversed scored. Higher score indicate a greater connection with nature.
Results for this outcome have not been posted.
Assesses opinions towards the importance of pro-environmental behaviors. Consists of 17 items that are rated from 1(not at all important) to 7 (extremely important). Higher total scores indicate a greater level of importance of pro-environmental behaviors.
Results for this outcome have not been posted.
Assesses individual differences in anthropomorphism. Consists of 15 items which are rated by a 10-point Likert scale. Higher total scores indicate a higher level of anthropomorphism.
Results for this outcome have not been posted.
Assesses beliefs of mind-body dualism. Consists of 11 items that are rated on a 7-point Likert scale. The total score is calculated after the appropriate items are reversed scored. Higher scores indicate a greater belief in mind-body dualism.
Results for this outcome have not been posted.
Measures perceived interpersonal connectedness. A single-item, pictorial measure of closeness. Images range from the self and other as completely separate to the self and other almost completely overlapping.
Results for this outcome have not been posted.
Assesses moral relativism and idealism. Consists of 20 items that are rated using a 9-point Likert scale (completely disagree to completely agree). Idealism scores are calculated by summing responses from items 1 to 10. Relativism scores are calculated by summing responses from items 11 to 20. Higher scores on items 1 to 10 indicate higher relativism and higher scores on items 11 to 20 higher idealism.
Results for this outcome have not been posted.
Assesses alcohol consumption, drinking behaviors, and alcohol-related problems. Consists of 10 items. The total score is calculated by summing all items. Higher scores indicate higher alcohol consumption. A score of 8 or more is considered to indicate hazardous or harmful alcohol use.
Results for this outcome have not been posted.
Assesses effects of Psilocybin. Consists of 86 items that assess eight categories of possible change in attitudes, mood, social effects, and behavior: 1. positive attitudes about life and/or self (17 items); 2. negative attitudes about life and/or self (17 items); 3. positive mood changes (4 items); 4. negative mood changes (4 items); 5. altruistic/positive social effects (8 items); 6. antisocial/negative social effects (8 items); 7. positive behavior changes (1 item); and 8. negative behavior changes (1item). Each item is rated using a 6-point rating scale from 0 (none, not at all) to 5 (extreme). Higher scores of each subscale indicate greater changes in that category.
Results for this outcome have not been posted.
Assesses frequency of urgent care and emergency room use. Consists of 26 items and 7 scales which include: Hypertension, High Cholesterol, Diabetes, Autoimmune, Musculoskeletal, Emergency Room Utilization, Urgent Care Utilization, Hospital Utilization, Facility Based Mental Health Care Utilization, Non-facility Based Mental Health Care Utilization. Items in each scale are scored by comparing follow-up scores to baseline scores. Positive difference indicates improved condition severity (Hypertension, High Cholesterol, Diabetes, Autoimmune, Musculoskeletal). Positive difference indicates reduced Emergency Room Utilization, Urgent Care Utilization, Hospital Utilization, Facility Based Mental Health Care Utilization, Non-facility Based Mental Health Care Utilization.
Results for this outcome have not been posted.
Assesses drug-related problems. Consists of 11 items. The total score is calculated by summing all items. Drug related problems are indicated with a score of 6 or more for men and a score of 2 or more for women.
Results for this outcome have not been posted.
Assesses tobacco use, motivation to quit, and dependence. Consists of 13 items. The baseline score of each item is compared to the follow-up score to assess changes. Higher scores indicate greater nicotine use.
Results for this outcome have not been posted.
Assesses different dimensions of the emotional experience. This scale consists of 60 words and phrases that describe different feelings and emotions. For each item participants rate to what extent they have felt this way during the past few weeks from 1 (very slightly or not at all) to 5 (extremely). The items are grouped into the following 4 subgroups and subscales; general dimension scales (negative affect, positive affect), basic negative emotion scales (fear, hostility, guilt, sadness), basic positive emotion scales (joviality, self-assurance, attentiveness), other affective states (shyness, fatigue, serenity, surprise). The items pertaining to each subscale are summed with higher scores indicating higher levels of each subscale.
Results for this outcome have not been posted.
Assesses different mental states induced by the interventions. Consists of 94 items which are rated by placing marks on a horizontal visual analogue scale (100 millimeters in length). The scale ranges from no, not more than usual (on the left) to yes, very much more than usual (on the right). The items are scored by measuring the millimeters from the low end of the scale to the participant's mark (from 0 to 100).
Results for this outcome have not been posted.
Assesses sleep quality. Consists of 19 self-rated questions and 5 questions rated by the bed partner or roommate (if one is available). Only self-rated questions are included in the scoring. The 19 self-rated items are combined to form seven "component" scores, each of which has a range of 0-3 points. In all cases, a score of "0" indicates no difficulty, while a score of "3" indicates severe difficulty. The seven component scores are then added to yield one "global" score, with a range of 0-21 points, "0" indicating no difficulty and "21" indicating severe difficulties in all areas.
Results for this outcome have not been posted.
Assesses readiness to change. Consists of 30 items rated from 1(strongly disagree ) to 5 (strongly agree). Subscales include: Precontemplation, Contemplation, Action, and Maintenance. Subscale scores are calculated by averaging the items in each subscale. The total score is calculated by summing the subscales Contemplation, Action, Maintenance and subtracting Precontemplation. Higher score indicate greater readiness to change.
Results for this outcome have not been posted.
Assesses difficult experiences induced by the interventions. Consists of 26 items that are rated from 0 (none; not at all) to 5 (extreme; more than ever before in my life). Participants are asked to rate the degree to which at any time during the previous session they experienced the following phenomena. Items are grouped into the following subscales: fear, grief, physical distress, insanity, isolation, death, and paranoia. Scores of each item are transformed into a percentage of the highest possible score. Subscale scores are calculated by averaging the transformed scores of the items in each subscale. The total score is the average of all the transformed item scores, with higher scores indicating more challenging experiences.
Results for this outcome have not been posted.
Assesses individual meaning in life. Participants are asked to name up to seven domains that they judge to be important to their individual meaning in life.Then they will rate their current level of satisfaction in each of these domains using a seven-point Likert scale (range, -3 to +3) and rate the importance of each of their chosen areas using a eight-point adjectival scale (range, 0 to 7). Higher total score indicate a greater meaning in life.
Results for this outcome have not been posted.
Assesses different experiential aspects of psilocybin. Consists of 44 items which provides scale scores for each of seven domains of mystical experiences: Internal Unity (6 items); External Unity (6 items); Transcendence of Time and Space (8 items); Ineffability and Paradoxicality (5 items); Sense of Sacredness (7 items); Noetic Quality (4 items). Participants are asked to look back on the extended session that they have just experienced and to rate the degree of their experience of the following phenomena. Each item is rated from 0 (none; not at all) to 5 (extreme; more than ever before in my life and stronger than 4). Total scores are expressed as a proportion of the maximum possible score.
Results for this outcome have not been posted.
Assesses quality of life and functionality. Consists of 16 items which are rated from 1 (very poor) to 5 (very good). Total score involves summing only the first 14 items to yield a raw total score. The raw total score ranges from 14 to 70. The raw total score is transformed into a percentage, with higher percentages indicating greater quality of life.
Results for this outcome have not been posted.
Measures state and trait anxiety. Consist of 40 items: 20 items measuring S-Anxiey and 20 items measuring T-Anxiety. State Anxiety Scale (S-Anxiety) evaluates the current state of anxiety. The Trait Anxiety Scale (T-Anxiety) evaluates relatively stable aspects of anxiety. The S-Anxiety scale assesses the intensity of current feelings "at this moment" from 1(not at all) to 4 (very much so). The T-Anxiety scale assesses the frequency of feelings "in general" from 1 (almost never) to 4 (almost always). The range of scores for each subtest is 20-80, with higher scores indicating greater anxiety.
Results for this outcome have not been posted.
Measures different OCD dimensions. Consists of 20 items assessing two core dimensions of OCD: harm avoidance (10 items) and incompleteness (10 items). Each item is rated from 0: never applies to me to 4: always applies to me. Higher scores on questions assessing harm avoidance indicates greater levels of harm avoidance. Higher scores on questions assessing incompleteness indicates higher levels of incompleteness.
Results for this outcome have not been posted.
An inventory of OCD symptoms. Consist of 18 items that are rated on a 5-point Likert scale. Total scores range from 0 to 72, with higher scores indicating more severe OCD symptoms.
Results for this outcome have not been posted.
Measures dysfunctional beliefs in obsessive-compulsive disorder. Consists of 44 items that are rated on a seven-point Likert scale, ranging from 1 (disagree very much) to 7 (agree very much). It contains three subscales: overestimations of threat and responsibility for harm (RT subscale), importance and control of intrusive thoughts (ICT subscale), and perfectionism and the need for certainty (PC subscale), with higher scores indicating higher levels of each sub-scale.
Results for this outcome have not been posted.
Assesses symptom severity and treatment response. Consists of 4 items that are rated on a 7-point Likert scale. Symptom severity scores range from 1 (normal) through to 7 (amongst the most severely ill patients). Treatment response scores range from 1 (very much improved) through to 7 (very much worse). Each component is rated separately; this measure does not yield a global score. Higher scores indicate greater symptom severity and lower treatment response.
Results for this outcome have not been posted.
Assesses individual differences in generalized optimism versus pessimism. Consists of 10 items that are rated from 0 (I agree a lot) to 4 (I disagree a lot). Of the 10 items, 3 items measure optimism, 3 items measure pessimism, and 4 items serve as fillers. Total scores are calculated by summing all items for a total ranging from 0 to 24.There are no "cut-offs" for optimism or pessimism; this measure is used as a continuous dimension of variability.
Results for this outcome have not been posted.
Assesses OCD symptoms across five dimensions: (1) obsessional thoughts about harm to oneself or others; (2) obsessional impulses to harm oneself or others; (3) contamination obsessions and washing compulsions; (4) checking compulsions; and (5) dressing/grooming compulsions. Consists of 39 items that are rated from 0 (not at all) to 4 (very much). Items within each domain are summed for subscale scores. All items are summed for a total score with higher scores indicating greater symptom severity.
Results for this outcome have not been posted.
Assesses individual variation in identification of several motor actions and activities. Comprises 25 items of various motor actions or activities, of which each can be endorsed and interpreted on a binary response scale as either a literal motor action or a meaningful outcome-oriented behavior. Greater number of items responded literally or meaningfully indicate more literal or meaningful, outcome-oriented behaviors, respectively.
Results for this outcome have not been posted.
Assesses reactions to research participation. Consists of 26 items (each rated from 1-5) assessing various aspects of participation-related reactions, which can be parsed into 5 subscales: perceptions of participation, personal benefits, emotional reactions, perceived drawbacks, and global evaluation. Higher subscale scores indicate greater extent of respective reactions.
Results for this outcome have not been posted.
Assesses depression symptoms. Consists of 21 items and uses a 0 to 3 severity scale. Total scores range from 0 to 63, with higher scores indicating more severe depression.
Results for this outcome have not been posted.
Resting-state brain connectivity will be assessed before and 48 hours after treatment. Neuronal activation induced by OCD-relevant provocative stimuli will be assessed 48 hours after the treatment.
Results for this outcome have not been posted.
Collected over 13 weeks. Non-serious events are listed at a 5% frequency threshold.
| Group | Deaths | Serious | Other |
|---|---|---|---|
| Psilocybin | 0/14 (0%) | 1/14 (7.1%) | 12/14 (85.7%) |
| Niacin | 0/14 (0%) | 0/14 (0%) | 6/14 (42.9%) |
| Psilocybin-Unblinded | 0/14 (0%) | 0/14 (0%) | 10/14 (71.4%) |
| Event | Psilocybin | Niacin | Psilocybin-Unblinded |
|---|---|---|---|
| Suicidal ideationPsychiatric disorders | 1/14 | 0/14 | 0/14 |
| Event | Psilocybin | Niacin | Psilocybin-Unblinded |
|---|---|---|---|
| DizzinessNervous system disorders | 3/14 | 2/14 | 6/14 |
| Visual perceptual changesPsychiatric disorders | 5/14 | 0/14 | 0/14 |
| NauseaGastrointestinal disorders | 5/14 | 2/14 | 4/14 |
| HeadacheNervous system disorders | 4/14 | 2/14 | 4/14 |
| ParesthesiaNervous system disorders | 4/14 | 2/14 | 2/14 |
| AnxietyPsychiatric disorders | 3/14 | 0/14 | 0/14 |
| FlushingCardiac disorders | 1/14 | 3/14 | 0/14 |
| Mood labilityPsychiatric disorders | 1/14 | 0/14 | 2/14 |
| HypertensionCardiac disorders | 1/14 | 0/14 | 0/14 |
| Suicidal ideationPsychiatric disorders | 1/14 | 0/14 | 0/14 |
| Age, Continuous(years) | Psilocybin | Niacin | Total |
|---|---|---|---|
| Mean | 35.5 ± 11.78 | 32.93 ± 12.44 | 34.22 ± 12.05 |
| Sex/Gender, Customized(Participants) | Psilocybin | Niacin | Total |
|---|---|---|---|
| Female | 6 | 8 | 14 |
| Male | 7 | 6 | 13 |
| Trans/Non-binary | 1 | 0 | 1 |
| Ethnicity (NIH/OMB)(Participants) | Psilocybin | Niacin | Total |
|---|---|---|---|
| Hispanic or Latino | 0 | 1 | 1 |
| Not Hispanic or Latino | 14 | 13 | 27 |
| Unknown or Not Reported | 0 | 0 | 0 |
| Race (NIH/OMB)(Participants) | Psilocybin | Niacin | Total |
|---|---|---|---|
| American Indian or Alaska Native | 0 | 0 | 0 |
| Asian | 0 | 1 | 1 |
| Native Hawaiian or Other Pacific Islander | 0 | 0 | 0 |
| Black or African American | 0 | 0 | 0 |
| White | 14 | 13 | 27 |
| More than one race | 0 | 0 | 0 |
| Unknown or Not Reported | 0 | 0 | 0 |
| Region of Enrollment(participants) | Psilocybin | Niacin | Total |
|---|---|---|---|
| United States | 14 | 14 | 28 |
| Education(Participants) | Psilocybin | Niacin | Total |
|---|---|---|---|
| High School or less | 0 | 1 | 1 |
| Some college | 3 | 4 | 7 |
| College graduate | 7 | 8 | 15 |
| Postgraduate | 4 | 1 | 5 |
| Obsessive Compulsive Disorder (OCD) Severity(score on a scale) | Psilocybin | Niacin | Total |
|---|---|---|---|
| Mean | 26.36 ± 4.63 | 27.21 ± 3.31 | 26.79 ± 3.98 |
| Current Medication(Participants) | Psilocybin | Niacin | Total |
|---|---|---|---|
| None | 8 | 9 | 17 |
| Required washout | 6 | 5 | 11 |
1 further baseline measures are reported on the registry.
PDFs hosted by the registry, ClinicalTrials.gov.
Plan to share: No
Ran from Nov 2018 to primary completion in Jul 2024, 68 months.
Results were first posted in Oct 2026, 2 years 2 months after primary completion.
Of 13 phase 1 interventional studies under Obsessive-Compulsive Disorder, half reached primary completion within 30 months of starting (the median), counting those still running; a quarter within 18 and three quarters within 57. This study's 68 months is above that.
How these figures are worked out, and which studies are left out of them.
From the registry record's own update history. This site started tracking changes on Sep 25, 2026; for anything earlier, see the record history on ClinicalTrials.gov ↗
This study is completed, as verified in Aug 2025. You cannot join it, but the record below documents what was studied.
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Studies of the drug tested here: Psilocybin
Obsessive-Compulsive Disorder →