Psychedelic Psychotherapy
Dr. Robin Carhart-Harriss
DR. ROBIN CARHART-HARRIS - Head of Psychedelic Research | Faculty of Medicine, Imperial College London
Psychedelic means mind revealing. With these substances, we reveal aspects of the mind that are ordinarily not visible to us, opening a window of plasticity and the capacity for change.
Summary
- Classical psychedelics like psilocybin and LSD target the serotonin 2A receptor to stimulate brain plasticity, promoting the growth of new functional units and enhancing cognitive flexibility.
- Psychedelic therapy provides rapid and enduring mental health improvements, often following a single session, for conditions such as treatment-resistant depression, addiction, and anxiety.
- The REBUS model suggests these compounds relax entrenched, pathological beliefs, allowing for a "reboot" of the mind's internal models through a temporary state of increased sensitivity.
- Brain imaging shows that psychedelics cause the breakdown of the default mode network, leading to ego dissolution and a more open, interconnected pattern of communication across brain regions.
- Therapeutic outcomes are significantly driven by acute experiences of psychological insight and a sense of "reconnection" to the world, which helps recalibrate entrenched emotional landscapes.
Article
Psychedelic Psychotherapy
The Neuroscience And Therapeutic Potential Of Psychedelics
At the Biohacker Summit 2018 Toronto, held in Toronto, Canada, on 15 and 16 October 2018, Dr. Robin Carhart-Harriss offered a lucid, quietly radical account of psychedelic psychotherapy, one that brought together molecular pharmacology, brain imaging, psychiatry and the oldest human questions about suffering, identity and change.
His presentation, delivered on Monday, 15 October 2018, made a case that classic psychedelics such as psilocybin, LSD and DMT were not merely consciousness-altering curiosities, nor relics of a countercultural past. In his telling, they were precise biological tools that could, under carefully controlled conditions, loosen the grip of rigid mental habits and create the conditions for profound therapeutic change.
A Drug Experience That Challenged Psychiatry’s Old Logic
The striking promise of psychedelic therapy, Dr. Carhart-Harriss argued, lay in its departure from the dominant model of psychiatric medicine. Conventional antidepressants are typically taken daily, often indefinitely, in an effort to manage symptoms over time. Psychedelic therapy suggested something altogether different: a single or limited intervention that could produce fast and lasting effects.
“Rather than being chronically medicated, it is that you have a profound experience that then seems to endure,” Dr. Robin Carhart-Harriss said during the talk. “That is paradigm shifting in the context of a pharmacological intervention in mental health.”
That line captured the force of the moment. The promise here was not maintenance, but transformation. Not a chemical dampening of distress, but an intense, time-limited opening in which the mind might become newly capable of revision.
How Psychedelics Worked In The Brain
At the centre of the presentation was a simple pharmacological claim. Classic psychedelics, including psilocybin, LSD and DMT, act primarily by agonising the serotonin 2A receptor, or 5-HT2A receptor. These compounds resemble serotonin closely enough to hijack part of the brain’s signalling machinery and trigger a cascade of effects linked to plasticity.
Dr. Carhart-Harriss described this as an “entropic” hot state, a temporary increase in neural and psychological flexibility. In practical terms, the effect was to make the brain less constrained by its usual routines and more sensitive to context, both external and internal. Old patterns could loosen. New associations could form. The mind, usually held together by habit, expectation and defensive certainty, could become unusually open.
That openness, he suggested, was not incidental. It was the mechanism.
The REBUS Model And The Relaxation Of Rigid Beliefs
Much of the talk turned on the idea that mental suffering often involved beliefs that had become overly fixed. Depression could harden into a pessimistic worldview. Trauma could produce defensive certainties. Addiction could trap a person in repetitive, self-reinforcing patterns. Even when individuals knew, rationally, that some of their beliefs were distorted, those beliefs could remain emotionally sovereign.
Dr. Carhart-Harriss framed this through his REBUS model, shorthand for Relaxed Beliefs Under Psychedelics. The idea was as elegant as it was provocative: psychedelics temporarily softened the authority of entrenched internal models, allowing them to be revised.
“The solution to aberrant beliefs is quite simply to relax those beliefs in a time-limited plastic state and then work on their revision,” Dr. Robin Carhart-Harriss said. “That is what psychedelic therapy does essentially.”
This was not presented as mystical rhetoric, but as a working neuroscientific theory. The mind, in this account, is constantly predicting reality through internal models. Under psychedelics, those models lose some of their dominance. What follows can be disorienting, even frightening, but it may also allow a patient to escape the imprisoning certainty of pathological thought.
Ego Dissolution And The Breakdown Of The Default Mode Network
One of the most arresting sections of the lecture concerned what happens to the brain during the acute psychedelic state. Imaging studies, Dr. Carhart-Harriss explained, showed that large-scale brain networks became less rigidly segregated. In particular, the default mode network, often associated with introspection and self-referential thinking, appeared to disintegrate.
That breakdown correlated with one of the signature features of high-dose psychedelic experience: ego dissolution.
“Through a breakdown of internal models, people realize they have constructed their identity as an internal model,” he said. “It is not something absolute, as they perhaps assumed before they had this experience.”
This was a profound challenge to ordinary consciousness. The self, which usually feels fixed and indivisible, was revealed as contingent and constructed. The implication for therapy was immense. If identity itself could briefly become fluid, then perhaps longstanding emotional wounds, repetitive narratives and deadened forms of being need not remain permanent.
A More Connected Brain, And Sometimes A More Connected Life
Under psychedelics, Dr. Carhart-Harriss said, the brain did not simply lose structure. It also gained connectivity. Regions that normally communicated in narrow, highly specialised ways began to exchange signals more freely. The result was a more globally integrated pattern of communication, less cliquish, more open.
That neural picture seemed to mirror the subjective reports of many patients. They described not just perceptual changes, but a deepened sense of connection to the world, to others and to themselves.
“People often report a sense of an opening of the heart and an overwhelming sense of oneness,” Dr. Robin Carhart-Harriss said. “This feeling of interconnectedness is often what mediates their wellness when the treatment works.”
There was, in that observation, a striking convergence between neuroscience and testimony. The clinical language of reintegration sat beside reports that sounded almost spiritual. Yet the force of the evidence, as he presented it, lay in the fact that these experiences were not therapeutic ornament. They were often central to the outcome.
Insight As The Engine Of Recovery
The talk returned repeatedly to one theme: insight. Psychedelic, after all, means mind-revealing. Dr. Carhart-Harriss argued that these compounds could make previously hidden aspects of experience newly visible, allowing individuals to see their own assumptions, wounds and patterns with unusual clarity.
“Insight mediates the revision and recalibration of beliefs so that they can be more in tune and more harmonious with our experience of the world,” he said.
That sentence carried the presentation’s deepest ambition. The goal was not simply symptom relief, though that mattered enormously. It was also a restoration of fit between self and reality. For some patients, this appeared to happen with remarkable speed.
Studies he cited pointed to rapid and enduring reductions in treatment-resistant depression, existential distress and addiction. In some cases, improvements emerged a day after treatment and were strongest weeks later. For patients who had spent years cycling through medications and therapies, the effect appeared almost implausible.
The Clinical Promise, And The Necessary Caution
Dr. Carhart-Harriss did not present psychedelics as miracle drugs. He stressed their sensitivity to context, the importance of psychological support and the fact that the acute experience could be deeply challenging. He also warned against rushing to embrace trends such as microdosing without stronger evidence.
Still, the broader clinical picture was hard to ignore. Classical psychedelics appeared to have low addiction potential, relatively low toxicity and a therapeutic profile unlike most psychiatric interventions. Population studies, he noted, had even found associations between psychedelic use and lower rates of psychological distress and suicidality, an anomaly among drugs of potential misuse.
What was emerging, then, was not simply a new treatment, but a different philosophy of mental healthcare. It suggested that people might heal not only by suppressing symptoms, but by entering, surviving and learning from an intense altered state that made change possible.
A Medicine Of Openness
By the end of the session at Biohacker Summit 2018 Toronto, Dr. Robin Carhart-Harriss had sketched a model of psychedelic psychotherapy that was at once rigorously biological and profoundly human. These substances acted on receptors, networks and neural plasticity. But their real significance lay in what they made possible: the loosening of certainty, the revision of identity, the recovery of perspective.
For a field long dominated by chronic medication and incremental relief, that amounted to a quiet revolution. Psychedelic therapy, as he described it, did not promise escape from the mind. It offered, instead, a way of seeing it more clearly, and perhaps, in that rare opening, changing it.
Part of Biohacker Summit 2018 Toronto