Dr Robin Carhart Harris The Science Of Psychedelics For Mental Health

High-Level Overview

Andrew Huberman sits down with Dr. Robin Carhart-Harris, distinguished professor of neurology and psychiatry at the University of California, San Francisco, and formerly the head of a pioneering psychedelic research center in London. The conversation covers the whole landscape of classic psychedelics: where the word came from, how they act on the serotonin 2A receptor, what actually happens in a clinical psilocybin session, why music and eye masks are standard, and what his brain imaging studies reveal about connectivity and even brain anatomy after a single high dose. They also dig into microdosing, placebo effects, anorexia and fibromyalgia trials, MDMA therapy, DMT, ego dissolution, relapse, and the slow path toward FDA approval.

The tone is curious, careful and warm. Huberman is openly admiring and asks long, layered questions, while Carhart-Harris repeatedly tempers excitement with caveats about small samples, unpublished data and the limits of what science currently knows. The conversation moves between history, neuroscience, first-hand clinical detail and policy, with philosophical detours into the unconscious, the self and what it means for a drug to reveal the mind.

The Discussion Explores:

• The origin of the word psychedelic and the tension between defining these drugs by pharmacology or by subjective experience
• Microdosing versus macrodosing, and a self-blinded study in which placebo matched microdosing
• What a clinical psilocybin session looks like: two therapists, eye masks, carefully built music, and the mantra of trust, let go, be open
• Increased global brain connectivity during and after psilocybin, and its link to recovery from depression
• A first-time-use study showing lasting changes in brain wiring after one 25-milligram dose
• Emerging trials in anorexia and fibromyalgia, and why expectancy did not predict psilocybin's effects
• MDMA, psilocybin-MDMA combinations, DMT, 5-MeO-DMT and the neuroscience of ego dissolution
• Relapse, integration, and the legal and regulatory road ahead for MDMA and psilocybin

Deep Dive into Main Ideas

What Makes a Drug Psychedelic

Carhart-Harris starts with where the word came from. In the 1950s the British psychiatrist Humphrey Osmond, then working in Canada, was unhappy that drugs like mescaline and LSD were classed as psychotomimetics, meaning drugs that mimic psychosis. He felt their effects went well beyond that. While trading ideas with Aldous Huxley, Osmond came up with psychedelic, built from the ancient Greek psyche (mind, or more literally soul) and a root meaning to reveal or make visible. Carhart-Harris likes the term because it says nothing about whether the experience will be good or bad. It simply reveals the psyche, which can be hellish or heavenly.

A recent consensus statement defines classic psychedelics pharmacologically, as compounds that act on the serotonin 2A receptor. Carhart-Harris accepts that this is useful but argues that you cannot leave out the phenomenology, the subjective experience, if you stay true to where the word came from. Huberman asks whether this revealing is like blindsight, where blind people guess correctly about things they cannot consciously see. Carhart-Harris says that is different: blindsight is non-conscious processing, whereas psychedelics bring up what depth psychologists call the unconscious. That includes Freud's personal unconscious of repressed, painful and traumatic material and Jung's collective unconscious. The older therapy literature describing repressed material surfacing, strong emotional release and insight under LSD and psilocybin is what drew him into the field. He says compounds like ketamine, MDMA or cannabis alone would never have captured the world's attention the way classic psychedelics have.

Microdosing, Dosing and the Power of Placebo

A microdose is usually defined as a sub-perceptible dose, one that does not produce a noticeable altered state, typically taken on a schedule such as one day on and one or two days off. For LSD, the threshold where sensitive people start to feel something is roughly 10 to 12 micrograms. Advocates claim microdosing improves well-being and perhaps creativity, but Carhart-Harris says the compelling evidence is not there yet. Microdosing studies are hard and expensive to run properly with placebo controls, and one promising New Zealand study has not yet been published.

He describes a creative citizen-science study led by his Imperial College colleague Balázs Szigeti. Participants blinded themselves by putting their own LSD microdoses and empty placebo capsules into identical capsules, shuffling them and tracking them with QR codes. They also tried mushrooms, but people burped up the taste, so non-psychoactive mushroom material was added to the placebos. The result: microdosing did not convincingly beat placebo. People who got placebo but believed they had microdosed did as well as those who truly had. Most of the effect came from expecting to be microdosed, what he calls a victory for the placebo response. It stirred controversy because people did not want to believe it, but as the two agree, "Science is not about what you want to believe."

On doses, clinical trials typically use 25 milligrams of psilocybin. Carhart-Harris stresses that nobody knows exactly how that compares with dried mushrooms and warns listeners not to use his answer to calibrate their own use. His rough estimate is that psilocybin makes up around 1 percent of mushroom mass, so one gram of mushrooms would contain about 10 milligrams. Huberman later points out a dangerous confusion: an LSD dose measured in micrograms can still be a full psychedelic dose, so the word microgram does not mean microdose.

Inside a Psilocybin Therapy Session

Carhart-Harris says the evidence that the experience itself drives healing is not a hunch. Independent teams keep finding that the strength of certain experiences, rated on subjective scales, reliably predicts therapeutic outcomes. The standard setup is very similar across sites: two people, ideally mental health professionals such as a psychiatrist or clinical psychologist, sit with the patient, who wears an eye mask and listens to music throughout. The music is spacious and wordless at first, becomes atmospheric, and then deliberately draws out emotion, with strings coming in as the drug takes stronger hold. He notes that no one has properly tested whether the music is essential, even though every major trial uses it. A skeptic could even call this music therapy, which is why he writes psychedelic-therapy with a hyphen, as a combination treatment whose parts likely work together.

The guiding mantra he learned when visiting Johns Hopkins, which he attributes to Bill Richards, is "trust, let go be open." Trust refers to the relationship with the therapists. His team measures it with a single rating on the morning of dosing, and it significantly predicts both the quality of the experience and outcomes weeks or months later. Letting go, a readiness to surrender rather than resist, also predicts response. Being open means being willing to face difficult material, which is especially hard for patients carrying trauma. A student of his, Ari Brouwer, is studying the phases of the experience: the early phase tends to be dominated by anxiety and struggle, the later phase by something different. Carhart-Harris explains that the early struggle is usually against the drug effects themselves. As the normal certainty about the world and the self breaks down, the two classic fears are that you are going mad or dying, even when you know you have taken a psychedelic.

Global Connectivity, the Entropic Brain and Lasting Change

In imaging studies, the brain normally communicates mostly within separate modules, such as the visual system talking to itself. Under psilocybin, and later LSD and DMT, communication spreads across modules, which his team calls increased global functional connectivity, and the effect tracks how intense the experience is. Computational models suggest the serotonin 2A receptor drives this. Asked whether connectivity causes the experience or runs in parallel, Carhart-Harris argues that causality is circular: brain and mind influence each other.

Crucially, the effect persists. In two depression cohorts, his team saw reduced modularity the day after psilocybin therapy and again three weeks later, and the size of that change correlated with how much symptoms improved. He cautions against overreading this, since sharper cognition is sometimes linked to more modularity, but suggests it reflects a more flexible brain. Huberman compares very linear thinkers with expansive, associative ones, and the two agree that health may involve being able to move along that continuum. Depression, like a hollow in a landscape, is easy to fall into and hard to climb out of, and comes with the bias that nothing will ever change. Opening up the brain may relate to opening up the mind.

On developing drugs that act on the same receptors without any trip, Carhart-Harris is skeptical. He finds the logic unconvincing and suspects wishful thinking, since patients and the medical system would both find such a drug convenient. He says no selective serotonin 2A agonist that lacks psychedelic effects is currently licensed in psychiatry. If one emerges, he expects it to look like the familiar model of a daily pill rather than psychedelic therapy, though he hopes it works for patients' sake.

A First-Time Psychedelic Study and Rewiring After One Dose

Carhart-Harris describes a completed but unpublished study of healthy, middle-aged volunteers (average age around 40, roughly equal men and women) who had never taken a psychedelic. Each first received a 1-milligram placebo-like dose and then 25 milligrams, with EEG recorded during the sessions and MRI scans before and after. All the changes appeared only with the 25-milligram dose. Well-being improved significantly. EEG showed what he calls the entropic brain effect: brain activity becomes more complex, less predictable and richer in information, and the bigger the trip, the bigger the effect, a finding that has now been replicated many times.

The most exciting result came from diffusion tensor imaging of the brain's white matter wiring. Two major tracts connecting the prefrontal cortex with the thalamus and striatum showed decreased axial diffusivity, which may mean stronger tract integrity. That is the direction seen as a brain matures from infancy to adulthood, and the opposite of what happens with aging and age-related disease. An independent analyst re-ran the data with a free-water correction she expected might erase the result, and it came through stronger. Participants also improved on a cognitive flexibility task after the high dose but not after placebo. Carhart-Harris stresses that it is one study, the anatomical change did not correlate with the psychological outcomes, and what it means functionally is still unknown.

Anorexia, Fibromyalgia and Why Placebo Does Not Explain It

His team's anorexia trial uses three dosing sessions, and with 19 patients through it, he reports fewer obsessive thoughts about food, more willingness to eat healthier amounts and improved weight at long follow-up. He emphasizes the trial is ongoing and unpublished. Huberman notes that anorexia is the most deadly psychiatric illness. A fibromyalgia study, run by his team in London, gives a single 25-milligram dose to people with widespread chronic pain, a condition long dismissed as psychosomatic. About eight people have been treated and it is going very well, he says, with profound experiences reported. Patients are not asked to focus on their pain. He warned colleagues not to assume hidden trauma lies behind every case, recalling psychoanalysis's troubles with false memories.

On placebo, he describes the psilocybin versus escitalopram (Lexapro) trial published in the New England Journal of Medicine in 2022. The escitalopram arm received a tiny psilocybin dose so everyone could be told they were getting psilocybin. Most participants expected psilocybin to work better. Yet expectancy before the trial predicted improvement with escitalopram on nearly every measure, while it predicted improvement with psilocybin on none of roughly a dozen scales. He sees this as a serious blow to the idea that psychedelic therapy is just a super-placebo, which makes the question of what it actually does even more intriguing.

MDMA, Combinations, DMT and Ego Dissolution

MDMA therapy is more interpersonal: patients talk more, likely use eye masks less, and MDMA trials use the sometimes-criticized language of an inner healer. Huberman describes his own therapeutic MDMA session, in which he asked for the music to be turned off because it pulled his attention away from the issues he wanted to address. Carhart-Harris says psilocybin can reach the core of suffering reliably but sometimes aggressively, triggering defenses in people with PTSD, while MDMA makes it easier and safer to revisit trauma, though perhaps not as deeply. He sees the classics as more honest, since the psyche is hell as well as heaven. He is open to underground practitioners' use of psilocybin-MDMA combinations as possible trial-and-error learning worth studying, in the spirit of precision medicine, though neither he nor Huberman endorses self-experimentation.

LSD is rarely used in trials largely for practical reasons: its effects last eight hours or more, and the FDA wanted even psilocybin participants kept for eight hours after dosing, which makes for very long staff days. DMT, by contrast, is "a rocket ship" if psilocybin is a ship leaving port. It is a direct serotonin 2A agonist, less potent than psilocybin by weight but overwhelming at standard doses, and often smoked or vaped, as is the related 5-MeO-DMT. People tend to describe 5-MeO-DMT as more reliably dissolving the sense of self and less visual. Huberman shares veterans' descriptions of DMT after ibogaine treatment as the most profound experience of their lives. Carhart-Harris explains the rule that a psychedelic's potency tracks how strongly it binds the 2A receptor, which is why LSD works in microgram doses.

Ego dissolution, he says, is not just a loss but a positive sense of connection to other people and the world, along with the insight that the self's boundaries are partly a construction. Huberman compares this to the brain, where everything is ultimately connected, and to family trees, where the lines we draw are a choice. Carhart-Harris notes that 2A receptors are concentrated in the evolutionarily recent cortex that expanded most in humans, and suggests psychedelics spread out, rather than shut off, the activity of that self-building system. In one of his studies, cocaine inflated the ego while psychedelics dissolved it.

Integration, Relapse and Practice

Asked how long integration lasts, Carhart-Harris quotes Jack Kornfield: "after the ecstasy, the laundry." Psychedelics give people a leg up to do very difficult work, but the work is lifelong. Since clinics cannot support patients forever, he suggests integration eventually becomes a practice, like meditation, which he sees as a valuable complement. He quotes a former colleague's line that psychedelic therapy lets you "sit with rather than sit on" difficult feelings, in contrast to daily medication.

He is candid about the paradox: the ego can return, sometimes with a vengeance, and in treatment-resistant depression relapse by three months is more the rule than the exception. Some early patients remain well years later, but most would need more sessions, which the law forbids once a trial ends. He calls that painful situation a sick joke.

The Legal and Regulatory Landscape

Huberman lays out the players: academic labs, underground therapists, a street market where fentanyl contamination is now showing up (citing Peter Attia's podcast), pharma, and the FDA and law enforcement. In Oakland, psilocybin is decriminalized, which is not the same as legal. Carhart-Harris says some head shops there sell mushrooms without licenses, and one church claims religious rights.

The key step is phase 3 trials, usually two successful ones, followed by FDA review. MAPS has completed two phase 3 trials of MDMA therapy for PTSD, with published remission rates of about 67 percent, and a decision could come that year, with rollout as early as the next in a best case. Open questions include who will supply the drug, what training therapists will need and who can refer patients, with a physician likely required nearby because of MDMA's cardiac risks. Psilocybin is several years behind: Compass's phase 3 trials for treatment-resistant depression have just begun, with one journalistic estimate of approval around 2026. Meanwhile smaller trials are exploring methamphetamine use disorder, Parkinson's, chronic back pain, bipolar disorder, OCD and addiction. Both men hope the field avoids the fate of gene therapy, which was set back for years by a single tragedy. Carhart-Harris argues psychiatric treatments have barely changed since the 1950s and that psychedelic therapy is a real paradigm challenge, while stressing that people who prefer conventional options should keep them.

Conclusion

This episode is a thorough, measured tour of psychedelic science from someone who helped build the field. Carhart-Harris argues that the psychedelic experience itself, guided by trust, surrender and openness and supported by music and skilled therapists, is central to psilocybin's effects on depression, and that these effects are not simply placebo. His imaging work suggests the brain becomes more globally connected, more complex and possibly structurally rewired after even one high dose, though he is careful to label much of it early. He is frank that microdosing lacks evidence, relapse is common and ongoing integration matters. Listeners interested in neuroscience, mental health treatment or the coming regulatory changes will find the full conversation rich with detail.

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