Nature Communications
August 3, 2026
Frederik Gudmundsen, Julia Czurylo, Daniel Ryskamp Rijsketic et al.
Serotonergic psychedelics show therapeutic potential across neuropsychiatric disorders despite transient acute effects. These compounds share serotonin 2 A receptor agonism but differ in broader pharmacology, motivating a systematic comparison of their neurobiological effects. Here, we use [18 F]FDG-PET in rats to assess acute and one-week effects of psilocybin, LSD, and 2C-B on brain metabolic...
Translational Psychiatry
July 15, 2026
Annette Johansen, Pontus Plavén-sigray, Martin K Madsen et al.
Psychedelics such as psilocybin have been linked to enhanced neuroplasticity and symptom relief in affective disorders, but the neurobiological mechanisms and impact of environmental context remain unclear. Here, we tested whether a single dose of psilocybin (0.3 mg/kg) alters synaptic density in healthy individuals and whether setting-dependent subjective experience shapes this effect. Fifteen...
Nature Communications
June 24, 2026
Drummond E-Wen Mcculloch, Anders S. Olsen, Brice Ozenne et al.
A prominent theory of psychedelics is that they increase brain entropy. Thirteen studies have evaluated psychedelic effects on fMRI brain entropy, each applying a distinct measure. Here we evaluated these metrics in an independent 28-participant healthy cohort with 121 pre- and post-psilocybin fMRI scans. We assessed relations between brain entropy and objective and subjective psychedelic drug...
Journal of psychopharmacology (Oxford, England)
May 29, 2026
Kristoffer Brendstrup‐brix, Brice Ozenne, Patrick M. Fisher et al.
Patients with chronic cluster headache (CCH) suffer from poor sleep, which may impact their brain microstructure and parenchymal clearance of waste products. Psilocybin has shown promise for the treatment of CCH and has been linked to increased neuroplasticity with possible influences on brain microstructure. To investigate the effects of psilocybin on sleep, brain water diffusivity, and...
bioRxiv
April 13, 2026
Anders S. Olsen, Kristian Larsen, Drummond E. Mcculloch et al.
Abstract Psilocybin and other serotonergic drugs acutely alter human brain function and large-scale connectivity as measured with BOLD fMRI, but whether these effects are frequency-specific remains unknown. We applied multitaper spectral and cross-spectral analyses to resting-state fMRI data from 28 healthy volunteers scanned multiple times acutely following oral psilocybin administration (0.2...
Nature Medicine
April 1, 2026
Manesh Girn, Manoj K. Doss, Leor Roseman et al.
8 citations
Psychedelic drugs are re-emerging as promising scientific and clinical tools. However, despite a rapidly expanding literature on their therapeutic value, the neural mechanisms underlying psychedelic effects remain unclear. Resting-state functional magnetic resonance imaging studies of acute psychedelic effects, conducted independently by several research groups, have so far yielded fragmented...
medRxiv
January 16, 2026
Kristian Larsen, Patrick M. Fisher, Drummond E. Mcculloch et al.
1 citation
Classical psychedelics have regained interest for their potential to treat psychiatric and neurological disorders, and explore neural mechanisms supporting perception, cognition, and mood. Acute psychedelic effects have been linked to increases in brain complexity and entropy, but it is unclear if these changes are specific to psychedelics or reflect more general psychoactive effects. Here, we...
Research Square
October 10, 2025
Gitte M. Knudsen, Annette Johansen, Pontus Plavén-sigray et al.
Abstract Psychedelics such as psilocybin have been linked to enhanced neuroplasticity and symptom relief in affective disorders, but the neurobiological mechanisms and impact of environmen-tal context remain unclear. Here, we tested whether a single dose of psilocybin alters synap-tic density in healthy individuals and whether setting-dependent subjective experience shapes this effect. Fifteen...
medRxiv
June 18, 2025
Drummond E-Wen Mcculloch, Kristian Larsen, Annette Johansen et al.
preprint
In this study, we provide the first study to integrate molecular and functional neuroimaging during psychedelic drug effects in humans. Using simultaneous PET-MRI technology, we describe multiple brain actions of lysergic acid diethylamide (LSD) in healthy volunteers. We quantify the occupancy of LSD at cerebral serotonin 2A receptors and show that LSD increases global cerebral blood flow and...
Journal of Psychopharmacology
February 28, 2025
Dea Siggaard Stenbæk, Emil Deleuran Poulsen, Marie Katrine Klose Nielsen et al.
15 citations
Background: Psilocybin, a serotonin 2A receptor agonist with psychedelic properties, shows promise as a novel treatment for alcohol use disorder (AUD). While current studies involve two dosing sessions, the effects of a single dose have not been investigated. Aims: To investigate the pharmacokinetics, feasibility, safety and efficacy of single-dose psilocybin therapy in AUD. Methods: This...
Journal of cerebral blood flow and metabolism : official journal of the International Society of Cerebral Blood Flow and Metabolism
February 26, 2025
Kristian Larsen, Ulrich Lindberg, Brice Ozenne et al.
9 citations
Psilocin, the active metabolite of psilocybin, is a psychedelic and agonist at the serotonin 2A receptor (5-HT2AR) that has shown positive therapeutic effects for brain disorders such as depression. To elucidate the brain effects of psilocybin, we directly compared the acute effects of 5-HT2AR agonist (psilocybin) and antagonist (ketanserin) on cerebral blood flow (CBF) using pseudo-continuous...
The British Journal of Psychiatry
December 5, 2024
Emma S Høgsted, Vincent Beliveau, Brice Ozenne et al.
4 citations
Background Using [ 18 F]altanserin, a serotonin 2A receptor (5-HT 2A R) antagonist Positron Emission Tomography (PET) tracer, a positive association between cortical 5-HT 2A R binding and the inward-directed facets of neuroticism has been demonstrated in healthy individuals. Psilocybin, a 5-HT 2A R agonist, shows promise for the treatment of depression, reducing neuroticism and mood symptoms...
Journal of Cerebral Blood Flow & Metabolism
November 29, 2024
Frederick A. Bagdasarian, Kristian Larsen, Deng Hong et al.
1 citation
Understanding neuromodulatory effects of serotonin 2A receptor (5-HT 2A R) agonists with diverse pharmacological profiles is relevant to advancing psychedelic-related drug applications. We performed simultaneous positron emission tomography (PET) and pharmacological magnetic resonance imaging (phMRI) in anesthetized nonhuman primates (NHP; N = 3) to examine partial agonists with varying 5-HT 2A...
Proceedings on CD-ROM - International Society for Magnetic Resonance in Medicine. Scientific Meeting and Exhibition/Proceedings of the International Society for Magnetic Resonance in Medicine, Scientific Meeting and Exhibition
November 26, 2024
Ande Bagdasarian, Kristian Larsen, Patrick M. Fisher et al.
Motivation: Acute effects of psychedelic drugs are under-reported in neuroimaging studies, warranting further investigation of their immediate pharmacology to explore the potential to monitor treatment response with imaging. Goal(s): Our goal was to assess acute impacts of serotonergic (psychedelic and non-psychedelic) agonists on hemodynamics in non-human primates (NHP). Approach:...
Research Square
August 23, 2024
Mathias E. Jensen, Dea Siggaard Stenbæk, Catharina Messell et al.
1 citation
Abstract Background Psilocybin, a serotonin 2A receptor agonist with psychedelic properties, shows promise as a novel treatment for alcohol use disorder (AUD). While current studies involve two dosing sessions, the effects a single dose have not been investigated. Aims To investigate the pharmacokinetics, feasibility, safety, and efficacy of single-dose psilocybin therapy in AUD. Methods This...
Journal of Psychopharmacology
August 13, 2024
Oliver Rumle Hovmand, Dea Siggaard Stenbæk, M. Madsen et al.
9 citations
Background: Psychedelic substances reliably induce marked altered states of consciousness (ASC), which may be important for lasting effects and clinical outcomes of psychedelic intervention. Several instruments are available to measure the acute psychedelic experience, of which the Five Dimensional Altered States of Consciousness Questionnaire (5D-ASC) is commonly used. The questionnaire can be...
European Neuropsychopharmacology
August 9, 2024
Friederike Holze, M. Madsen, Claus Svarer et al.
16 citations
The serotonin 2A (5-HT2A) receptor is an important target for drug development and the main receptor through which classical psychedelics elucidate their hallucinogenic effects. The 5-HT2A receptor antagonist ketanserin has frequently been used as a tool to block the receptor. Here, we establish the dose-occupancy relation of ketanserin and the cerebral 5-HT2A receptor in healthy participants...
May 28, 2024
Frederik Gudmundsen, Julia Czurylo, Camilla Trang Vo et al.
1 citation
preprint
Serotonergic psychedelic drugs have shown promising benefits in trials for various neuropsychiatric disorders. While the acute effects of these psychedelics last only a few hours, the positive therapeutic effects can persist long after a single administration. Serotonergic psychedelics produce their psychedelic effects by activating serotonin 2A receptors, but they differ in other...
Journal of Psychoactive Drugs
January 15, 2024
Oliver Rumle Hovmand, Mathias Ebbesen Jensen, Tobias Søgaard Juul et al.
6 citations
Research suggests positive changes in both well-being and psychiatric symptoms following a psychedelic experience. One explanation may be the ability of psychedelic compounds to occasion mystical-type experiences. The Revised Mystical Experiences Questionnaire (MEQ30) is designed to assess the intensity and quality of such experiences. We examined the validity, reliability, and factor structure...
Headache The Journal of Head and Face Pain
2024
Anja Sofie Petersen, Inger Marie Sørensen, Harald Schiønning et al.
29 citations
Abstract Objective To evaluate the feasibility and prophylactic effect of psilocybin as well as its effects on hypothalamic functional connectivity (FC) in patients with chronic cluster headache (CCH). Background CCH is an excruciating and difficult‐to‐treat disorder with incompletely understood pathophysiology, although hypothalamic dysfunction has been implicated. Psilocybin may have...
Neuroscience Applied
December 30, 2023
Sophia Armand, Kristian Larsen, Martin K Madsen et al.
7 citations
The serotonergic psychedelic psilocybin acutely induces changes in emotional states. However, it remains unresolved whether psilocybin acutely modulates amygdala reactivity to emotions, a brain region critically involved in emotion processing. Using functional magnetic resonance imaging (fMRI), we examined in 26 healthy individuals whether amygdala responses to angry, fearful and neutral faces...
medRxiv
July 3, 2023
Drummond E-Wen Mcculloch, Anders S. Olsen, Brice Ozenne et al.
20 citations
preprint
A prominent theory of psychedelics is that they increase brain entropy. Twelve studies have evaluated psychedelic effects on fMRI brain entropy quantifications, no findings have been replicated. Here we evaluated these metrics in an independent 28-participant healthy cohort with 121 pre- and post-psilocybin fMRI scans. We assessed relations between brain entropy and plasma psilocin, brain...
Neuroimage
October 27, 2022
Anders Lykkebo-Valløe, Brice Ozenne, Sophia Armand et al.
44 citations
Our findings suggest that the acute perceptual psychedelic effects induced by psilocybin may stem from drug-level associated decreases in the occurrence and duration of lateral and medial frontoparietal connectivity motifs. We apply and argue for a modified approach to modeling eigenvectors produced by LEiDA that more fully acknowledges their underlying structure. Together these findings...
Frontiers in Psychology
October 5, 2022
Anna Søndergaard, Brice Ozenne, Sophia Armand et al.
35 citations
Background Psilocybin-induced mystical-type experiences are associated with lasting positive psychological outcomes. Recent studies indicate that trait mindfulness is increased 3 months after psilocybin intake, preceded by decreases in neocortical serotonin 2A receptor (5-HT 2A R) binding. However, the association between psilocybin-induced mystical-type experiences and subsequent changes in...
medRxiv
July 10, 2022
M. Madsen, Anja Sofie Petersen, Dea Siggaard Stenbæk et al.
5 citations
preprint
Abstract Chronic cluster headache (CCH) is an excruciating disorder of unknown pathophysiology, but hypothalamic dysfunction has been implicated. CCH is difficult to treat but on a case-basis, the psychedelic compound psilocybin is said to have beneficial effects. In this first-ever clinical trial ( NCT04280055 ), we evaluate in a small open-label study of CCH patients the feasibility and...