Imperial College London Centre for Psychedelic Research

Origins and Leadership

The story of Imperial College London's psychedelic research program is largely the story of Robin Carhart-Harris, a psychologist and neuroscientist who began working on psilocybin as a doctoral researcher under David Nutt around 2008–2009. Nutt, a professor of neuropsychopharmacology and former UK government chief drug adviser (controversially dismissed in 2009 for publicly stating that alcohol was more dangerous than cannabis and ecstasy), became the scientific director and provided the institutional credibility and pharmacological expertise to navigate regulatory barriers to Schedule I research in the UK.

The Psychedelic Research Group at Imperial was operating informally from around 2009, publishing its first peer-reviewed work from approximately 2011 onward. The Centre for Psychedelic Research was formally established in April 2019, shortly after Johns Hopkins launched its own centre — representing a transatlantic "coming out" of psychedelic science as a legitimate institutional enterprise. The Imperial centre is embedded within the Department of Brain Sciences and has access to world-class neuroimaging facilities, including fMRI, MEG, and high-density EEG systems.

Carhart-Harris relocated to the University of California, San Francisco (UCSF) in 2021 to lead their new Neuroscape Psychedelics Division, but the Imperial centre continued under the leadership of David Nutt and other senior colleagues including Leor Roseman and Christopher Timmermann. The research programmes Carhart-Harris established at Imperial continue, and his theoretical framework — the REBUS model — remains the most influential conceptual contribution from the centre.

Groundbreaking Studies

The 2012 PNAS study by Carhart-Harris and colleagues was the first neuroimaging investigation of psilocybin in the human brain. Using arterial spin labelling (ASL) perfusion fMRI — which measures cerebral blood flow rather than BOLD signal, giving more direct quantification of neural activity — the study demonstrated that psilocybin significantly decreased activity in the default mode network (DMN), particularly the posterior cingulate cortex and medial prefrontal cortex. Crucially, the degree of DMN suppression correlated with the subjective intensity of ego dissolution. This paper established the DMN as the neural correlate of the ordinary sense of self and psilocybin as a tool for experimentally manipulating self-related processing.

In 2016, the Imperial group published a landmark open-label trial of psilocybin in 20 patients with treatment-resistant depression (Carhart-Harris et al., The Lancet Psychiatry). This was the first modern study to administer psilocybin to patients rather than healthy volunteers. All 20 patients showed some reduction in depressive symptoms, with 47% meeting response criteria at five weeks and 42% in remission. While the absence of a control group meant causality could not be definitively established, the effect sizes and durability of response — in a population that had failed an average of four previous antidepressant treatments — were remarkable and justified the subsequent randomised trial.

The 2021 randomised controlled trial comparing psilocybin to escitalopram (a standard SSRI antidepressant) in NEJM was the most methodologically sophisticated psychedelic trial to date. Fifty-nine adults with moderate-to-severe major depressive disorder were randomised to two psilocybin sessions (25 mg each) plus six weeks of placebo tablets, or two very low "active placebo" psilocybin doses (1 mg) plus six weeks of escitalopram. On the primary outcome (QIDS-SR-16 depression scale at six weeks), the difference between groups did not reach statistical significance — but the psilocybin group showed numerically superior performance on nearly all secondary measures, including wellbeing, anhedonia, work and social functioning, and sexual dysfunction. The study concluded that psilocybin was "at least as effective" as escitalopram on the primary endpoint and showed advantages on multiple dimensions of functional recovery.

Theoretical Contributions

Imperial College's most enduring scientific contribution may be its theoretical frameworks for understanding how psychedelics alter consciousness. The entropic brain hypothesis, published by Carhart-Harris in Frontiers in Human Neuroscience in 2014, proposed that psychedelics increase the entropy of brain activity — shifting neural dynamics toward less constrained, more complex patterns. This framework drew on information theory and complexity science to explain why psychedelic states feel simultaneously more chaotic and more vivid than ordinary waking consciousness.

The REBUS (Relaxed Beliefs Under Psychedelics) model, published with Karl Friston in Pharmacological Reviews in 2019, integrated predictive coding theory with the entropic brain framework. Predictive coding holds that the brain is fundamentally a prediction machine, constantly generating top-down predictions about incoming sensory data and only propagating "prediction errors" — signals that don't match expectations — upward through the hierarchy. Under this model, the DMN encodes the highest-level beliefs and self-model that shape perception and cognition. Psilocybin, by activating 5-HT2A receptors on cortical layer V pyramidal neurons, reduces the precision weighting of these top-down predictions — effectively "relaxing" the brain's existing belief structures and allowing bottom-up sensory signals to gain influence. This explains hallucinations, emotional release, mystical unity experiences, and potentially therapeutic insight: all are consequences of temporarily loosening the grip of habitual, self-referential predictive models.

Imperial researchers have also advanced understanding of the distinct roles of 5-HT2A versus 5-HT1A receptor activation in the psychedelic experience. While 5-HT2A agonism is primarily responsible for perceptual and cognitive effects, 5-HT1A agonism (which psilocin also engages, though less potently) may contribute to the anxiolytic, sedative, and oceanic boundlessness components of the experience. Separating these receptor contributions through pharmacological challenge studies represents ongoing work with implications for developing more targeted next-generation compounds.

Current Research and Collaborators

The ACE (Accept, Connect, Embody) study, launched in 2022 and ongoing, is the most comprehensive neuroimaging investigation of psilocybin's therapeutic mechanisms ever conducted. It combines multiple neuroimaging modalities — fMRI, MEG, EEG, and MRS (magnetic resonance spectroscopy) — to map acute and lasting brain changes in patients with depression undergoing psilocybin therapy. The study is designed to identify specific neural biomarkers that predict clinical response, enabling precision medicine approaches to psilocybin treatment.

COMPASS Pathways has been a key industry collaborator of Imperial College, providing synthetic psilocybin and co-funding research that has contributed to the COMP360 clinical development programme. The Beckley Foundation, led by Amanda Feilding, has had a long-standing research partnership with Imperial, co-funding studies since the early 2010s. Cross-Atlantic collaborations with Johns Hopkins, UCSF, and NYU are common — the 2016 cancer anxiety trials were a dual-institution effort, and multiple research groups share data, methodology, and personnel through informal networks formalised by organisations like the Psychedelic Science Funders Collaborative.

Current PhD and postdoctoral researchers at Imperial are investigating topics including the role of the claustrum in psychedelic action, psilocybin for end-of-life existential distress, and the electrophysiological signatures of mystical experience using high-density EEG. The centre trains the next generation of psychedelic researchers from across Europe and beyond, functioning as a training hub within the broader global research ecosystem.

Frequently Asked Questions

Who founded Imperial College's psychedelic research program?

Robin Carhart-Harris began the research program as a doctoral student under David Nutt around 2008–2009. Nutt, a prominent neuropharmacologist and former UK chief drug adviser, provided the institutional leadership and pharmacological expertise. The Centre for Psychedelic Research was formally established in April 2019.

What did the 2012 fMRI study show?

The 2012 study was the first neuroimaging investigation of psilocybin in the human brain. It found that psilocybin significantly decreased activity in the default mode network — especially the posterior cingulate cortex and medial prefrontal cortex — and that the degree of suppression correlated with subjectively reported ego dissolution, establishing the DMN as a neural correlate of the sense of self.

What is the REBUS model?

REBUS (Relaxed Beliefs Under Psychedelics), published in 2019 by Carhart-Harris and Friston, is a predictive coding framework that proposes psilocybin reduces the brain's top-down "belief" signals encoded in the DMN, allowing bottom-up sensory and emotional signals to gain unusual influence. This explains hallucinations, mystical experiences, and potentially the therapeutic value of psychedelic states.

What did the 2021 psilocybin vs escitalopram trial find?

The randomised trial in NEJM compared two 25 mg psilocybin sessions to six weeks of escitalopram in major depression. On the primary depression scale, the difference was not statistically significant. However, psilocybin showed numerical advantages on nearly all secondary outcomes including wellbeing, anhedonia, and sexual functioning, leading researchers to conclude psilocybin was at least as effective with additional functional benefits.

What was the first treatment-resistant depression trial?

The 2016 open-label trial published in The Lancet Psychiatry enrolled 20 patients who had failed multiple antidepressant treatments. All showed some symptom reduction; 47% met response criteria at five weeks and 42% were in remission. This groundbreaking study demonstrated psilocybin's potential in the most difficult-to-treat depression population.

What is the ACE study?

The ACE (Accept, Connect, Embody) study, launched in 2022, uses a multi-modal neuroimaging battery including fMRI, MEG, EEG, and spectroscopy to identify neural biomarkers of psilocybin's therapeutic effects. Its goal is to determine which specific brain changes during the acute psilocybin session predict long-term clinical benefit — a key step toward precision psychedelic medicine.

What is the entropic brain hypothesis?

Published in 2014, the entropic brain hypothesis proposes that psychedelics increase the entropy (informational complexity and randomness) of brain activity. This explains the richness and novelty of psychedelic experience as a genuine increase in the information content of neural dynamics, measurable through complexity metrics such as Lempel-Ziv complexity of EEG signals.

Who is David Nutt?

David Nutt is a professor of neuropsychopharmacology and scientific director of Imperial's Centre for Psychedelic Research. He is also known as the UK government's chief drug adviser (2008–2009) who was controversially dismissed after publishing evidence that alcohol was more dangerous than several illegal drugs. His expertise and institutional credibility have been central to establishing psychedelic research as legitimate science in the UK.

Does Imperial collaborate with COMPASS Pathways?

Yes. COMPASS Pathways has provided synthetic psilocybin (COMP360) and co-funded research at Imperial that has contributed to its clinical development programme. The Beckley Foundation has also had a long-standing partnership with Imperial, co-funding studies since the early 2010s. Cross-Atlantic collaborations with Johns Hopkins, UCSF, and NYU are also common.

Where is Robin Carhart-Harris now?

Carhart-Harris relocated to the University of California, San Francisco (UCSF) in 2021 to lead the new Neuroscape Psychedelics Division. The Imperial Centre for Psychedelic Research continues under David Nutt and other senior colleagues, and the research programmes and theoretical frameworks Carhart-Harris developed there remain highly influential.