Martin Madsen

Academic, Clinician, Scientist

Dr. Martin Madsen is a Danish physician and neurobiology researcher based in Copenhagen. Prior to his current position at Herlev Hospital, Dr. Madsen practiced medicine and conducted research while earning his PhD at the Neurobiology Research Unit (NRU) at Rigshospitalet. 

In 2012, while at NRU, Dr. Madsen won the Danish Regions’ Prize Award in Psychiatry. He has taught neurology and internal medicine at the occupational therapy program of Professionshøjskolen Metropol (Metropol College) since 2014. Dr. Madsen earned his MD at Københavns Universitet (University of Copenhagen) in 2016 and his undergraduate degree at Thompson Rivers University in Canada in 2009. 

Dr. Madsen’s research focuses on how modulation of the serotonin 5-HT2A receptor affects brain function and structure. Specifically, he uses neuroimaging techniques including Positron Emission Tomography (PET scans) and functional Magnetic Resonance Imaging (fMRI) to investigate the interactions between 5-HT2A and psilocybin and related tryptamine compounds. 

Dr. Madsen was the lead author on a January 2019 study which confirmed scientists’ hypothesis that the binding of psilocin to 5-HT2A produces the psychedelic experience associated with psilocybin.1 The findings, later covered by Psychedelic Science Review, revealed a positive correlation between 5-HT2A occupancy (the number of receptors occupied by the drug), plasma levels of psilocin, and subjective intensity of the psychedelic experience. A separate January 2019 study he co-authored concluded that increases in the personality trait of openness are not related to differences in the availability of 5-HT2A in individuals.2 

In March 2020, Dr. Madsen and his colleagues published the first neuroimaging study investigating psilocybin’s long-term effects.3 The results confirmed the association between psilocybin intake and long-term increases in mindfulness. Curiously, the study also found that mindfulness ratings correlated negatively with 5-HT2A activity. A Psychedelic Science Review article described the study in more detail. Dr. Madsen told Eric Dolan of PsyPost, “Psilocybin seems to increase mindful awareness in a long-term fashion in people who have never tried a psychedelic drug. Our results also show that subtle changes in brain serotonin 2A receptor levels and/or the serotonin levels probably contributes to these changes.”

An August 2020 Neuropsychopharmacology publication by Madsen and colleagues further elucidated the key relationship between psilocin levels in plasma and the neurobiological and behavioral effects of psilocybin.4 Dr. Madsen also contributed to a study of how individual differences in pre-drug 5-HT2A binding predict a user’s psilocybin experience. The research, published in October 2020, revealed that more 5-HT2A binding activity was associated with shorter peak plateau durations, lower mystical experience questionnaire scores, and lengthier returns to normal waking consciousness.5

A video of Dr. Madsen’s talks about serotonin receptor occupancy and psilocybin at the 2018 Colloquium on Psychedelic Psychiatry is available online. He also spoke at the ICPR 2020 conference, presenting his research mapping psilocybin’s effects on resting-state functional connectivity via fMRI. 

  1. Madsen MK, Fisher PM, Burmester D, et al. Psychedelic effects of psilocybin correlate with serotonin 2A receptor occupancy and plasma psilocin levels. Neuropsychopharmacology. 2019;44:1328-1334. doi:10.1038/s41386-019-0324-9
  2. Stenbæk DS, Kristiansen S, Burmester D, et al. Trait Openness and serotonin 2A receptors in healthy volunteers: A positron emission tomography study. Human brain mapping. 2019;40:2117-2124. doi:10.1002/hbm.24511
  3. Madsen MK, Fisher PM, Stenbæk DS, et al. A single psilocybin dose is associated with long-term increased mindfulness, preceded by a proportional change in neocortical 5-HT2A receptor binding. European neuropsychopharmacology. 2020;33:71-80. doi:10.1016/j.euroneuro.2020.02.001
  4. Madsen MK, Knudsen, GM. Plasma psilocin critically determines behavioral and neurobiological effects of psilocybin. Neuropsychopharmacol. 2021;46(1):257–258.
  5. Stenbæk DS, Madsen MK, Ozenne B, et al. Brain serotonin 2A receptor binding predicts subjective temporal and mystical effects of psilocybin in healthy humans. J Psychopharmacol. Published online October 8, 2020.