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Johannes G. Ramaekers

Maastricht University

113 papers in the library · 4,349 citations · publishing 2003-2026

Papers

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Sex Differences in Acute Responses to Psychedelics: Evidence for Greater Subjective Intensity and Impairment in Female Participants

bioRxiv (Cold Spring Harbor Laboratory) July 13, 2026 Natasha L. Mason, Eline Chm Haijen-Bongers, Kim P. C. Kuypers et al.

Serotonergic psychedelics are advancing as psychiatric treatments, yet acute responses vary between individuals and the contribution of sex, a fundamental biological variable, remains largely unexamined. We pooled two double-blind, placebo-controlled studies in healthy volunteers (N = 72; 31 male, 41 female) comparing psilocybin 15 mg, 2C-B 20 mg, and LSD 50 μg. Linear mixed models tested sex...

Pivotal physical states: The somatic equivalent to pivotal mental states

Journal of Psychedelic Studies June 26, 2026 Malin V. Uthaug, Jack G. Allocca, Martha N. Havenith et al.

Abstract Background The Pivotal Mental States (PiMS) construct posits that psychedelics and other stress-inducing practices, such as fasting and hypoxia, can evoke transformative mental states through increased serotonin receptor activation in the brain. These states are associated with enhanced cognitive flexibility, accelerated associative learning, and psychological insights that may...

Brain-body integromics of the ayahuasca experience.

Biomedicine & pharmacotherapy = Biomedecine & pharmacotherapie June 1, 2026 Francisco Madrid-Gambin, Pablo Mallaroni, Noemí Haro et al.

Ayahuasca is a psychoactive brew containing N,N-dimethyltryptamine (DMT) and β-carboline alkaloids that induces marked alterations in perception, emotion and self-referential processing. However, the multiscale biological organization linking peripheral metabolism, brain network dynamics, neurochemistry, and subjective experience in humans remains poorly understood. Here, we applied an...

Evaluating the evidence for repressed memory recovery in psychedelic contexts

Psychopharmacology April 29, 2026 Anne-Fiona Griesfeller, Lotte Kooman, Lilian Kloft-Heller et al.

RATIONALE: Reports of resurfaced repressed memories during psychedelic experiences have circulated for decades and still emerge today. However, the veracity of repressed memories remains debated, and the mechanisms through which psychedelics might recover alleged repressed memories are unclear. OBJECTIVES: This scoping review aimed to provide an overview of the literature on repressed memory in...

Subjective and neurocognitive profiling of clinical doses of 3,4-methylenedioxymethamphetamine (MDMA) in healthy volunteers: implications for therapeutic use

Molecular Psychiatry April 8, 2026 Johannes G. Ramaekers, Kim P. C. Kuypers, Franz X. Vollenweider 1 citation

MDMA's history spans military experimentation, recreational use, and clinical trials for PTSD treatment, reflecting both promise and controversy. While studies in heavy users suggested possible neurotoxicity, evidence remains inconclusive. Clinical trials show that one to three sessions of MDMA-assisted psychotherapy can alleviate PTSD symptoms, yet regulators have criticized inadequate...

An international mega-analysis of psychedelic drug effects on brain circuit function

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...

GH001 vs Placebo in Patients With Treatment-Resistant Depression

JAMA Psychiatry March 25, 2026 Wiesław Jerzy Cubała, Malek Bajbouj, Michael Bauer et al. 3 citations

Importance: Few pharmacotherapies are approved for treatment-resistant depression, and many patients do not achieve remission following treatment with those therapies. Objective: To examine the efficacy and safety of single-day treatment with a synthetic formulation of inhaled mebufotenin (GH001) vs placebo in patients with treatment-resistant depression. Design, Setting, and Participants: This...

Spatiotemporal mapping of brain organisation following the administration of 2C-B and psilocybin

Molecular Psychiatry February 3, 2026 Pablo Mallaroni, S. Parker Singleton, Natasha L. Mason et al.

As psychedelic-assisted psychotherapy gains momentum, clinical investigation of next-generation psychedelics may lead to novel compounds tailored for specific populations. 2,5-dimethoxy-4-bromophenethylamine (2C-B) is a psychedelic phenethylamine reported to produce less dysphoria and subjective impairment than the psychedelic tryptamine psilocybin. Despite its popularity among recreational...

A Virtual Clinical Trial of Psychedelics to Treat Patients With Disorders of Consciousness

Advanced Science November 20, 2025 Paolo Cardone, Charlotte Martial, Yonatan Sanz Perl et al. 3 citations

Abstract Disorders of consciousness (DoC), including unresponsive wakefulness syndrome (UWS) and minimally conscious state (MCS), have limited treatment options and are characterized by low complexity of brain activity. Recent research suggests that psychedelic drugs, which enhance the complexity of brain activity, could offer promising therapies. Here, individualized whole‐brain computational...

Unmixing the Psychedelic Connectome: Brain Network Traits of Psilocybin

November 17, 2025 Krishna Prasad Bhavaraju, Natasha L. Mason, Pablo Mallaroni et al. preprint

Abstract Psilocybin induces profound alterations in consciousness, yet prevailing neural models often describe a monolithic change in brain connectivity that may not fully capture the multifaceted nature of the psychedelic state. To test the hypothesis of a composite neural state, this study applied a robust, data-driven framework, Connectome Independent Component Analysis (connICA) with...

Cannabis Perturbs Dynamic Brain States

Biological Psychiatry October 21, 2025 Katharina S Lege, Pablo Mallaroni, Sepehr Mortaheb et al. 1 citation

Background The impact of acute cannabis exposure on brain function and cognitive performance varies among individuals. Acute effects of cannabis on behavior may be absent or benign in chronic users, while occasional users experience significant impairment in day-to-day operations. It is hypothesized that repeated cannabis use induces neuroadaptations leading to tolerance and desensitization,...

Exploring the importance of bodyset for the psychedelic experience and beyond

Journal of Psychedelic Studies September 8, 2025 Malin Vedøy Uthaug, Giancarlo Allocca, Martha N. Havenith et al. 1 citation

AbstractBackgroundResearch has shown that psychedelics may have therapeutic potential in treating mental disorders like depression and anxiety. However, the mechanisms and actions underlying their effects are still not fully understood. Similarly, while the significance of mindset and setting in shaping psychedelic experiences and therapeutic outcomes is well established, information about the...

Between enhancement and risk: A critical review of psychedelic microdosing

Current Opinion in Psychology August 6, 2025 Iva Totomanova, Eline Haijen, Petra P M Hurks et al. 5 citations

Microdosing psychedelics, the regular use of low doses of LSD or psilocybin, have attracted growing public and scientific interest. This review synthesizes findings from 57 human studies on psychological and physiological outcomes in clinical and non-clinical populations. Reported benefits include improved mood, enhanced cognition, social functioning, and mental health, although findings are...

Syner-G: Antidepressant action of psychedelics at the glutamatergic interface of brain, behavior and the immune system

July 3, 2025 Natasha L. Mason, Pablo-Alexandre Mallaroni, Attila Szabo et al. preprint

Promising results have emerged in the use of psychedelic drugs for treating depression. Despite multiple neural models attempting to elucidate the acute psychedelic experience, and an increased focus on potential mechanisms driving persistent change, the connections between the acute state and the enduring therapeutic outcomes remain elusive. This targeted review aims to bridge this gap by...

An international Delphi consensus for reporting of setting in psychedelic clinical trials.

Nature Medicine June 3, 2025 Chloé Pronovost-Morgan, Kyle T. Greenway, Leor Roseman et al. 26 citations

Psychedelic substances exhibit complex interactions with the 'set and setting' of use, that is, the mental state of the user and the environment in which a psychedelic experience takes place. Despite these contextual variables' known importance, psychedelic research has lacked methodological rigor in reporting extra-pharmacological factors. This study aimed to generate consensus-based...

Safety and cognitive pharmacodynamics following dose escalations with 3-methylmethcathinone (3-MMC): a first in human, designer drug study.

Neuropsychopharmacology : official publication of the American College of Neuropsychopharmacology June 1, 2025 Johannes G. Ramaekers, Johannes T. Reckweg, Natasha L. Mason et al. 8 citations

3-Methylmethcathinone (3-MMC) is a designer drug that belongs to the group of synthetic cathinones. The compound has been scheduled in many jurisdictions because of public health concerns associated with excessive use. To date, there are no clinical studies that have evaluated the risk profile of 3-MMC in the recreational range of low to moderate doses. The current, first-in-human study (N =...

Metabolomic profiling of cannabis use and cannabis intoxication in humans.

Neuropsychopharmacology : official publication of the American College of Neuropsychopharmacology May 1, 2025 Francisco Madrid-Gambin, Noemí Haro, Natasha L. Mason et al. 4 citations

Acute intoxication from Δ9-tetrahydrocannabinol (THC, the primary active ingredient of cannabis) can lead to neurocognitive impairment and interference with day-to-day operations, such as driving. Present evaluations of THC-induced impairment in legal settings rely on biological drug tests that solely establish cannabis use, rather than cannabis impairment. The current study evaluated the...

Low to moderate doses of 3-methylmethcathinone (3-MMC) produce analgesic effects in healthy volunteers: a proof of principle study with a designer drug

Psychopharmacology April 30, 2025 Johannes G. Ramaekers, Johannes T. Reckweg, Natasha L. Mason et al. 4 citations

3-Methylmethcathinone (3-MMC) is a synthetic cathinone that has been scheduled in many jurisdictions after it appeared on the consumer market as a designer drug or "legal high". At present, there are no medical applications for synthetic cathinones, but in the past cathinone and other compounds that are structurally related to amphetamine have been evaluated and recognized for their intrinsic...

Ayahuasca enhances the formation of hippocampal-dependent episodic memory without impacting false memory susceptibility in experienced ayahuasca users: An observational study.

Journal of psychopharmacology (Oxford, England) April 1, 2025 Manoj K. Doss, Lilian Kloft, Natasha L. Mason et al. 5 citations

Ayahuasca is an Amazonian brew with 5-HT2A-dependent psychedelic effects taken by religious groups globally. Recently, psychedelics have been shown to impair the formation of recollections (hippocampal-dependent episodic memory for specific details) and potentially distort memory while remembering. However, psychedelics spare or enhance the formation of familiarity-based memory...

Benefits and Challenges of Ultra-Fast, Short-Acting Psychedelics in the Treatment of Depression

American Journal of Psychiatry 2025 Johannes G. Ramaekers, Johannes T. Reckweg, Natasha L. Mason 25 citations

Unlike classical antidepressants, psychedelics such as psilocybin have been shown to induce a rapid antidepressant response. In the wake of this development, interest has emerged in ultra-fast, short-acting psychedelics such as 5-methoxy-N,N-dimethyltryptamine (5-MeO-DMT) and N,N-dimethyltryptamine (DMT) with the expectation that these can produce rapid antidepressant effects following an...

Exploring 5-MeO-DMT as a pharmacological model for deconstructed consciousness.

Neuroscience of Consciousness 2025 Christopher Timmermann, James W. Sanders, David Reydellet et al. 19 citations

5-MeO-DMT is a short-acting psychedelic that is anecdotally reported to induce a radical disruption of the self and a paradoxical quality of aroused, waking awareness that is nevertheless devoid of any specific perceptual contents. Here, we conducted an exploratory observational study of the phenomenological and neuronal effects of this compound. We collected micro-phenomenological interviews,...

Evaluation of the peak experience scale as a rapid assessment tool for the strength of a psychoactive experience with 5-MeO-DMT.

Frontiers in Psychology 2025 Johannes T. Reckweg, Natasha L. Mason, Eef L. Theunissen et al. 2 citations

A three-item Peak Experience Scale (PES) was developed to rapidly evaluate the strength of the psychoactive experience, and to guide the dosing regimen, of the psychedelic 5-methoxy-N,N-dimethyltryptamine (5-MeO-DMT; mebufotenin). This paper aims to compare the PES with a range of established questionnaires designed to evaluate the psychedelic experience. Data were gathered from three separate...

Potential therapeutic effects of psychedelics in small doses: Is there a role for microdosing in psychiatry?

International review of neurobiology 2025 Iva Totomanova, Eline Haijen, Petra P M Hurks et al.

Clinical trials using full doses of psychedelics have provided preliminary evidence supporting their safety and efficacy in treating a variety of physical and psychological conditions. Anecdotal reports indicate that even very small amounts of these substances may provide therapeutic benefits, though robust clinical studies are still needed. This chapter reviews the current experimental studies...

The forgotten psychedelic: Spatiotemporal mapping of brain organisation following the administration of 2C-B and psilocybin

bioRxiv (Cold Spring Harbor Laboratory) October 22, 2024 Pablo Mallaroni, S. Parker Singleton, Natasha L. Mason et al. 2 citations preprint

As psychedelic-assisted psychotherapy gains momentum, clinical investigation of next-generation psychedelics may lead to novel compounds tailored for specific populations. 2,5-dimethoxy-4-bromophenethylamine (2C-B) is a psychedelic phenethylamine reported to produce less dysphoria and subjective impairment than the psychedelic tryptamine psilocybin. Despite its popularity among recreational...