Nature
August 1, 2024
Joshua S. Siegel, Subha Subramanian, Demetrius Perry et al.
241 citations
A single high dose of psilocybin (25 mg) massively disrupts functional connectivity in the human brain, causing more than threefold greater change than methylphenidate (40 mg). These changes are driven by desynchronization across spatial scales, dissolving network distinctions by reducing correlations within and anticorrelations between networks. The strongest effects occur in the default mode network, which is connected to the anterior hippocampus and is thought to create the sense of space, time, and self. Individual differences in connectivity changes are strongly linked to the subjective psychedelic experience. A persistent decrease in connectivity between the anterior hippocampus and default mode network lasts for weeks, suggesting a neuroanatomical correlate of the therapeutic and proplasticity effects of psychedelics.
JAMA Psychiatry
December 7, 2022
Joshua S. Siegel, James E. Daily, Demetrius Perry et al.
168 citations
Between 2019 and 2022, 25 U.S. states considered 74 bills related to psychedelic drugs, with 10 enacted and 32 still active. The number of bills introduced each year rose from 5 in 2019 to 36 in 2022. Most bills (90%) specified psilocybin, and 58% proposed decriminalization, though few included medical oversight or licensure requirements. Early legislative efforts occurred in liberal states, but the partisan gap has narrowed, suggesting reform is becoming bipartisan. An analytic model based on marijuana legalization projects that a majority of states will legalize psychedelics by 2034 to 2037.
Psychopharmacology
January 22, 2021
J. Siegel, B. Palanca, B. Ances et al.
53 citations
A single 96-hour infusion of ketamine, co-administered with clonidine, is well tolerated and produces a rapid and sustained antidepressant response in over 50% of adults with treatment-resistant depression. In an open-label study of 23 adults, depressive symptoms dropped markedly from an average MADRS score of 29 at baseline to 9 one day after infusion, and remained reduced at 2 weeks (13) and 8 weeks (15). Brain imaging showed that the infusion normalized overconnectivity in the limbic system and between the subgenual anterior cingulate cortex and the default mode network, with response-dependent and treatment-dependent connectivity changes.
medRxiv
August 24, 2023
Subha Subramanian, Demetrius Perry, Caterina Gratton et al.
14 citations
preprint
Psilocybin disrupts connectivity across cortical networks and subcortical structures, producing more than three-fold greater acute changes in functional networks than methylphenidate. These changes are driven by desynchronization of brain activity across spatial scales, strongest in the default mode network (DMN), which is connected to the anterior hippocampus and thought to create our sense of self. Performing a perceptual task reduces psilocybin-induced network changes, suggesting a neurobiological basis for grounding during psychedelic therapy. Psilocybin induces a persistent decrease in functional connectivity between the anterior hippocampus and cortex (and DMN in particular), lasting for weeks but normalizing after six months. This persistent suppression of hippocampal-DMN connectivity represents a candidate neuroanatomical and mechanistic correlate for psilocybin's pro-plasticity and anti-depressant effects.
Nature Medicine
February 6, 2026
Joshua S. Siegel, Conor Liston, Ginger E. Nicol et al.
10 citations
Classic psychedelics, acting at the serotonin 5-HT2A receptor, alter brain function and consciousness. Research converges on two complementary processes: acute neural desynchronization, which destabilizes entrenched network patterns, and subacute neuroplasticity, which opens a window for psychological and behavioral change. Evidence of therapeutic response across neuropsychiatric indications is reviewed, integrating mechanistic findings. Challenges include discrepancies between preclinical evidence that non-hallucinogenic psychedelic analogs engage putative therapeutic mechanisms and clinical evidence linking subjective experience to therapeutic response, risks of enhanced neuroplasticity, and questions about trial design, scalability, and regulatory approval. The growth of psychedelic science may compel a rethinking of the relationship between subjective experience and biological change in psychiatry.
Nature Neuroscience
October 13, 2025
Jonah A. Padawer-Curry, Oliver J. Krentzman, Chao‐cheng Kuo et al.
9 citations
Psychedelics like psilocybin and DOI alter the brain's hemodynamic response, potentially disrupting the normal coupling between neuronal activity and blood flow. In human fMRI scans, psilocybin induced changes in hemodynamic response functions. In awake mice, DOI differentially affected the relationship between cortical excitatory neuronal activity and hemodynamic signals, both during whisker stimulation and at rest, leading to discordant changes in functional connectivity measures depending on whether they were based on neuronal or hemodynamic data. A selective serotonin-2A receptor antagonist reversed many of these effects. The findings indicate that the vasoactive effects of psychedelics must be considered when interpreting blood-based measures of brain function.
bioRxiv (Cold Spring Harbor Laboratory)
September 24, 2023
Xiaodan Wang, Jonah A. Padawer-Curry, Oliver J. Krentzman et al.
9 citations
preprint
Psychedelics show promise for treating mood disorders, but their effects on brain blood vessels have been overlooked. Psilocybin altered hemodynamic response functions in humans, suggesting changes in neurovascular coupling (NVC). Using wide-field optical imaging in awake mice, the psychedelic DOI (a serotonin-2A receptor agonist) partially altered task-based NVC but caused more pronounced NVC changes during rest, especially in association brain regions. Calcium and hemodynamic signals gave different accounts of resting-state functional connectivity under DOI. Co-administration with a 5-HT2A antagonist reversed many effects. The dissociation between neuronal and hemodynamic signals highlights the need to consider neurovascular effects when interpreting fMRI measures in psychedelic studies.
Translational Behavioral Medicine
October 17, 2024
Danielle R Adams, Heidi Allen, Ginger E. Nicol et al.
7 citations
Psychedelic-assisted psychotherapy (PAT) shows promise for treating PTSD, depression, and substance use disorders, with potential FDA approval of psilocybin-assisted therapy for depression by 2026. This commentary calls for implementation scientists to collaborate with PAT researchers and practitioners to bring these treatments into routine practice, especially in safety-net settings like Federally Qualified Health Centers and Veterans Affairs health systems that serve historically marginalized populations. Using the RE-AIM Framework, the authors outline how implementation science can contribute tools, methodologies, and approaches to ensure PAT is safe, effective, and accessible for underserved communities.
Scientific Data
June 5, 2025
Subha Subramanian, Travis Rick Renau, Demetrius Perry et al.
4 citations
A psychedelic drug, psilocybin, and a comparison drug, methylphenidate, produce distinct acute and persistent changes in brain networks measurable with precision functional mapping, a technique that improves signal detection by repeatedly scanning individuals. Seven healthy adults underwent extensive baseline brain imaging, imaging shortly after drug intake, and follow-up scans for up to two weeks. Four participants repeated the psilocybin protocol months later. The dataset includes resting-state and task-based functional MRI, structural scans, and subjective experience reports. The authors release this resource to help researchers study how psilocybin and methylphenidate alter brain network organization over time.
Nat Hum Behav
February 24, 2025
Ginger E. Nicol, Danielle R Adams, Eric J Lenze et al.
4 citations
Psychedelic-assisted therapy (PAT) combines medication with psychotherapy, but many questions remain about how it works, for whom, and in what context. To avoid the typical 17-year delay between research and clinical practice, implementation science can help by simultaneously studying safety, effectiveness, and real-world delivery. Methods like sequential multiple assignment randomized trials (SMART), hybrid study designs, and fidelity measurement can speed implementation while maintaining quality and safety. Substantial changes to regulations, training, and access are needed to accommodate this multimodal therapy outside research settings. The authors advocate proceeding with accelerated caution.
Biological Psychiatry
April 29, 2024
Joshua S. Siegel, Subha Subramanian, Nico U.f. Dosenbach et al.
3 citations
No Summary
The Journal of Clinical Psychiatry
June 10, 2026
Jacob T. Steinle, Suraj Shankar, Joshua S. Siegel et al.
After adjusting for preexisting psychiatric conditions, the link between hallucinogen use and psychosis disappears. Among 273,466 people with substance-related hospital admissions, psychosis diagnoses were more common after hallucinogen-related admissions (16.4%) than after other substance admissions (6.6%). However, once clinical characteristics were accounted for, the increased risk became nonsignificant (hazard ratio 0.97). This suggests that observed associations between hallucinogens and psychosis are largely due to underlying mental health vulnerabilities, not a direct causal effect. The findings inform psychedelic policy by indicating that population-level data on hallucinogen safety may reflect preexisting risk factors.