Huberman LabThe Science of Psychedelics for Mental Health | Dr. Robin Carhart-Harris
At a glance
WHAT IT’S REALLY ABOUT
Psychedelics Rewire Depressed Brains: Inside Carhart-Harris’ Groundbreaking Trials
- Andrew Huberman interviews Dr. Robin Carhart-Harris about the science, mechanisms, and clinical applications of classic psychedelics such as psilocybin, LSD, and DMT, with a focus on depression and other difficult-to-treat conditions. Carhart-Harris explains what “psychedelic” really means, why subjective experience and ego dissolution matter, and how serotonin 2A receptor activation alters brain network dynamics. They review controlled trials showing rapid, often dramatic improvements in major depression, treatment-resistant depression, PTSD, anorexia, and fibromyalgia, and contrast macrodosing with the more weakly supported practice of microdosing. The conversation concludes with emerging data on structural brain changes after a single psilocybin session, the coming FDA decisions on MDMA and psilocybin therapies, and the ethical, regulatory, and practical challenges of integrating these treatments into mainstream psychiatry.
IDEAS WORTH REMEMBERING
5 ideasClassic Psychedelics Are Defined Both by Receptor Pharmacology and Subjective Experience
Carhart-Harris emphasizes that “classic psychedelics” are best defined in two ways: pharmacologically, as agonists at the serotonin 2A receptor (e.g., LSD, psilocybin, DMT), and phenomenologically, as drugs that reveal aspects of the psyche (unconscious material, transpersonal content). He argues you cannot ignore the subjective trip and still honestly call something a psychedelic; compounds that stimulate 5-HT2A without psychedelic phenomenology would be better viewed as a different drug class, more akin to SSRIs.
Psilocybin Macrodosing Shows Strong, Replicable Antidepressant Effects
In treatment-resistant and major depression, two guided psilocybin sessions (typically 25 mg, spaced 1–3 weeks apart) produce high remission rates—often around 60–70% in small trials—far exceeding typical SSRI outcomes in similar populations. These gains can last weeks to months, though many chronic, severely depressed patients eventually relapse, highlighting both the power and the limits of the intervention. Critically, the intensity and emotional depth of the acute experience robustly predict therapeutic benefit, supporting the view that “the trip” is a central mechanism, not an incidental side effect.
Microdosing Benefits Are Weak and Largely Explained by Expectation
A creative citizen-science study led by Carhart-Harris’ group asked LSD microdosers to self-blind by encapsulating their own microdoses and placebos and tracking outcomes. Those who thought they had taken LSD improved as much whether they actually had LSD or placebo, indicating that positive expectancy drove most of the reported benefits. Methodologically strong, long-duration, placebo-controlled microdosing trials are logistically hard and still sparse; current evidence for microdosing improving mood or creativity is suggestive at best and far weaker than for macrodosing plus therapy.
Psychedelics Temporarily Increase Brain Entropy and Global Connectivity, Then Leave Lasting Network Changes
Neuroimaging during psilocybin, LSD, and DMT shows decreased modularity and increased “global functional connectivity”: brain regions that normally communicate mostly within their own networks start communicating across networks. EEG measures reveal an “entropic brain” effect—greater informational complexity—that scales with subjective intensity. Importantly, in depression trials, a residual decrease in modularity (interpreted as more flexible, less “stuck” brain dynamics) persists for days to weeks and correlates with symptom improvement, suggesting a window of enhanced functional plasticity during which psychotherapy and life changes may consolidate more deeply.
A Single High-Dose Psilocybin Session Can Induce Structural Brain Changes
In a completed but not yet published study of healthy, psychedelic-naïve middle-aged volunteers, one 25 mg psilocybin session produced measurable changes in white matter tracts between prefrontal cortex, thalamus, and striatum, assessed via diffusion tensor imaging. Axial diffusivity decreased in these large tracts—an effect associated with increased tract integrity and seen in healthy neurodevelopment, and opposite to patterns of aging and neurodegeneration. Although correlations with cognitive and wellbeing improvements were modest, this suggests that a single macrodose can produce not only functional but also anatomical alterations in key control circuits.
WORDS WORTH SAVING
5 quotesPsychedelic literally means ‘mind-revealing’—these drugs make aspects of the psyche visible that are ordinarily not available to us.
— Dr. Robin Carhart-Harris
If it wasn’t for this action of the classic psychedelics—this revealing of the unconscious—I don’t think we’d be so interested in them.
— Dr. Robin Carhart-Harris
Science is not about what you want to believe. That right there is the beauty of science.
— Dr. Robin Carhart-Harris
Psychedelic therapy allows you to sit with rather than sit on [your pain], in a way that chronic pharmacotherapy often does not.
— Dr. Robin Carhart-Harris
Current treatments haven’t really progressed since the 1950s. Psychedelic therapy is a genuine paradigm challenge to that model of a pill every day.
— Dr. Robin Carhart-Harris
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