Podcast Summary

The OCD Stories – Episode 532

Guest: Dr. Sorcha O’Connor
Host: Stuart Ralph
Episode Title: The PsilOCD study investigating low-dose psilocybin for OCD
Date: April 5, 2026

Episode Overview

This episode delves into the PsilOCD study—the first controlled investigation in Europe of low-dose psilocybin as a potential treatment for obsessive-compulsive disorder (OCD). Dr. Sorcha O’Connor, lead researcher and neuroscientist, joins host Stuart Ralph to share background on the study, its methodology and outcomes, and what these findings could mean for the future of OCD treatment. The discussion covers how psilocybin works, what participants experienced in the trial, safety and limitations, and the possibility of integrating psychedelics within precision psychiatry and established therapeutic frameworks like ERP.

Key Discussion Points and Insights

Dr. O’Connor’s Background & Path to PsilOCD (02:27–03:37)

• Dr. O’Connor’s journey:
  • Began studying neuroscience aged 18, including a year abroad in Spain researching epigenetics and schizophrenia.
  • “I found myself more drawn to conditions like OCD and anxiety spectrum, conditions that I think can be slightly more malleable and slightly more amenable to psychological techniques.” (02:52)
  • Completed a master’s in cognitive neuroscience in Barcelona and a PhD at Imperial College London, focusing on the PsilOCD study.

What is Psilocybin? (04:01–04:58)

• Definition and context:
  • Psilocybin is a naturally occurring hallucinogenic substance found in many wild mushroom species (“magic mushrooms”).
  • At high doses: “Marked changes in perception, emotional shifts and trips.” (04:33)
  • At low doses: Emotional changes and increased openness, with minimal perceptual effects. This “gentle, emotional change” dose was used for the PsilOCD study.

Inspiration and Rationale for the Study (05:08–06:41)

• Initial inspiration:
  • Sparked by a 2006 pilot study by Moreno et al. at University of Arizona finding “all three doses elicited significant improvements in symptoms 24 hours after the dose.” (05:35)
  • Objective: Find a more accessible dose for those “who don’t necessarily want that element of loss of control, which I think rings true for a lot of people with OCD.” (06:23)
  • PsilOCD chose a 10mg dose, lower than most modern depression studies.

The Study Design (08:54–10:57)

• Participant journey:
  • Spanned just over two months; 19 participants (18 completers).
  • Rigor in selection: Excluded those with family history of psychotic/manic episodes or complex comorbidities.
  • Procedures:
    1. Screening, then 1 week of non-OCD-specific preparation sessions with two therapists.
    2. Placebo (1mg psilocybin—active but minimal perceptual effects).
    3. Four weeks of follow-up supportive therapy (not OCD-specific).
    4. Active dose (10mg psilocybin).
    5. Four more weeks of therapy and monitoring, including mechanistic measures (EEG, cognitive tests).
  • “The participant is treated the same after the placebo as after the experimental dose.” (10:57)

Participant Demographics and OCD Presentations (11:26–12:16)

• Ages 20–60; slightly more men than women; diverse themes (harm, contamination, taboo, identity, responsibility).
• Focused on moderate-to-severe OCD (“Y-BOCS over 16”) and minimal comorbidity.

Main Outcomes and Efficacy Findings (12:33–14:15)

• “Symptoms were significantly improved at the one week point. Then…drops below significance at two and four weeks.” (13:32)
• Among “completers,” improvement persisted for two weeks.
  • 39% achieved a “strong response” (defined as a >35% decrease in Y-BOCS).
  • 10/18 moved from moderate-severe to mild category after a single low dose with no OCD-specific therapy.
• “Psilocybin induces a period of openness… without something like ERP… we didn’t really capitalize on that.” (15:07)

Mechanisms: What Happens in the Brain? (19:26–24:37)

• Molecular Action:
  • Psilocybin acts via 5-HT2A serotonin receptors, affecting perception, emotions, and symbolic thinking.
  • At low doses: No “ego death” or strong visuals, “but people definitely had symbolic experiences.”
  • May briefly boost neuroplasticity via increased brain-derived neurotrophic factor (BDNF), as seen with exercise and certain foods.
  • “The brain is always molding itself to the environment and updating… In a condition like OCD, this is really relevant because I definitely see it as a condition of learning.” (21:46)
• ReBUS Model:
  • Robin Carhart-Harris’ “Relaxed Beliefs Under Psychedelics” theory describes how psychedelics temporarily relax entrenched predictive patterns, allowing new learning and perspective.

Therapeutic Implications and Future Applications (14:15–16:53, 35:41–38:02)

• Integration with therapy:
  • Psilocybin “streamlines” the learning window and could enhance ERP or other therapies.
  • “I personally see it as something that’s most likely to support existing therapy.” (07:26)
• Future of psychedelics in psychiatry:
  • Not a daily medicine—at most, spaced-out dosing.
  • Ongoing larger and higher-dose studies in the US (25–30mg); UK remains conservative with low-dose, which “resonates with many people with OCD.”

Trial Safety and Setting (28:56–33:31)

• Therapist support:
  • Two therapists with the participant throughout—“in a very nicely lit room, scandi aesthetic… scenes of nature and plants.” (29:21)
  • Present for safety, anxiety management—but no active ERP or OCD-specific therapy.
• Risks:
  • No serious adverse events; minor side effects (headache, dizziness, vivid dreams, or nightmares) generally unrelated or brief.
  • “People can have very challenging experiences... if the setting isn’t right.” (31:07)
• Importance:
  • Emphasis on set, setting, professional oversight, clean source—“Everything’s a double-edged sword, especially when it comes to psychology and how people feel.” (31:07)

Placebo & Expectancy Effects (34:11–35:22)

• Expectancy (“did you think this would help?”) was measured but did not predict improvement, supporting the clinical effect’s authenticity.

Limitations (38:22–42:18)

• Mechanistic assays (EEG markers of neuroplasticity and cognitive flexibility/metacognition) did not find significant changes after psilocybin compared to placebo.
• The disconnect: improvements in symptoms, but unclear mechanistic underpinning as measured.
  • “It improves symptoms, but not in the way that we thought mechanistically…” (41:14)
• “We don’t know exactly how SSRIs work either… if it’s safe and it works, is it crucial we know exactly how and why?” (42:18)

Looking Forward: The Future of Research (35:41–38:02, 43:12–47:27)

• Need for larger studies, multiple dosing arms, or ERP plus psilocybin arms for better understanding.
• “There is a big demand for a lower dose approach.” (36:45)
• In the future: Stratified, precision psychiatry (“personalized medicine”) approaches may help identify who benefits most.

Notable Quotes & Memorable Moments

• On therapy and medication integration:
  • “I personally don’t know if any pharmacological tool like psilocybin could fully supplant therapy and replace it.” (07:26)
  • “I see psilocybin as a real potential facilitator… really synergistic with therapy.” (22:53)
• On expectations and set/setting:
  • “It just shows you that actually it can be scary if it’s not done in the right set and setting.” (30:36)
  • “It’s so important that it’s done ethically and in a highly regulated way… safety was of the utmost concern.” (32:21)
• On the hopeful message for OCD:
  • “There’s always the capacity to improve.” (26:21)
  • “…It’s just a hopeful message for the medical side of OCD that there’s this potentially this other string or arm… people can choose from.” (47:14)
• On limitations and scientific unknowns:
  • “Some of these mechanisms are still slightly mysterious.” (41:55)
  • “…is it crucial we know exactly how and why? Probably not.” (42:18)
• On curiosity and growth:
  • “Be curious.” (44:48, 45:08)
  • “Stay childlike.” (45:24)

Important Timestamps

| Segment/Topic | Timestamp | |-----------------------------------------------|------------| | Dr. O’Connor’s background | 02:27–03:37| | What is psilocybin? | 04:01–04:58| | Inspiration for the study | 05:08–06:41| | Study design and participant journey | 08:54–10:57| | Participant demographics & OCD presentations | 11:26–12:16| | Main efficacy outcomes | 12:33–14:15| | Mechanisms: Brain effects of psilocybin | 19:26–24:37| | Therapeutic implications & future applications| 14:15–16:53, 35:41–38:02| | Safety, risks, and setting | 28:56–33:31| | Placebo/expectancy effects | 34:11–35:22| | Limitations (mechanistic assays) | 38:22–42:18| | Looking forward/precision psychiatry | 35:41–38:02, 43:12–47:27| | Personal reflections from Dr. O’Connor | 44:24–45:24|

What People with OCD Can Take From This Study (38:22–42:18, 46:18–47:27)

• There is growing scientific interest and funding in innovative treatments for OCD.
• Low-dose psilocybin administered with careful support can yield rapid but temporary symptom improvements in some people with OCD.
• Experience during studies is highly controlled and supportive; self-experimentation is not recommended.
• The evidence for long-lasting effects and exact mechanisms is still early and inconclusive.
• No strong safety concerns were found at this dose, but more data is needed.

“Hopefully over the next five years we’ll see really significant shifts, and then maybe people who are suited to it will be able to supplement their existing therapy programme with this type of intervention.” (46:18)

Final Takeaways

• The PsilOCD study offers an important early step—demonstrating both promise and limitations.
• Integrating psychedelics within therapy, notably at lower doses, could become an evidence-based future option for those with treatment-resistant OCD, or for whom current approaches fall short.
• Research is ongoing, and precision, personalization, and safety will remain key considerations as the field evolves.
• For now, therapy remains central, with psilocybin seen as a possible adjunct in the years to come.