Receptor interaction profiles of novel psychoactive tryptamines compared with classic hallucinogens

Exploring DMT: Endogenous role and therapeutic potential

N,N-Dimethyltryptamine (DMT) is a naturally occurring amine and psychedelic compound, found in plants, animals, and humans. While initial studies reported only trace amounts of DMT in mammalian brains, recent findings have identified alternative methylation pathways and DMT levels comparable to classical neurotransmitters in rodent brains, calling for a re-evaluation of its biological role and exploration of this inconsistency. This study evaluated DMT's biosynthetic pathways, focusing on indolethylamine N-methyltransferase (INMT) and its isoforms, and possible regulatory mechanisms, including alternative routes of synthesis and how physiological conditions, such as stress and hypoxia influence DMT levels. This review considers the impact of endogenous regulatory factors on DMT synthesis and degradation, particularly under conditions affecting monoamine oxidase (MAO) efficiency and activity. We also examined DMT's potential roles in various physiological processes, including neuroplasticity and neurogenesis, mitochondrial homeostasis, immunomodulation, and protection against hypoxia and oxidative stress. DMT's lipophilic properties allow it to cross cell membranes and activate intracellular 5-HT2A receptors, contributing to its role in neuroplasticity. This suggests DMT may act as an endogenous ligand for intracellular receptors, highlighting its broader biological significance beyond traditional receptor pathways. The widespread evolutionary presence of DMT's biosynthetic pathways across diverse species suggests it may play essential roles in various developmental stages and cellular adaptation to environmental challenges, highlighting the neurobiological significance of DMT and its potential clinical applications. We propose further research to explore the role of endogenous DMT, particularly as a potential neurotransmitter.

Acute dose-dependent effects and self-guided titration of continuous N,N-dimethyltryptamine infusions in a double-blind placebo-controlled study in healthy participants

N,N-dimethyltryptamine (DMT) is a serotonergic psychedelic that is known for its short-lasting effects when administered intravenously. Several studies have investigated the administration of intravenous boluses or combinations of a bolus and a subsequent continuous infusion. However, data on dose-dependent acute effects and pharmacokinetics of continuous DMT infusions are lacking. We used a double-blind, randomized, placebo-controlled, crossover design in 22 healthy participants (11 women, 11 men) who received placebo and DMT (0.6, 1.2, 1.8, and 2.4 mg/min) over an infusion duration of 120 min. We also tested a self-guided titration scheme that allowed participants to adjust the DMT dose rate at prespecified time points to achieve their desired level of subjective effects. Outcome measures included subjective effects, autonomic effects, adverse effects, plasma hormone concentrations, and pharmacokinetics up to 3 h after starting the infusion. DMT infusions exhibited dose-proportional pharmacokinetics and rapidly induced dose-dependent subjective effects that reached a plateau after 30 min. A ceiling effect was observed for "good drug effect" at 1.8 mg/min. The 2.4 mg/min dose of DMT induced greater anxious ego dissolution than the 1.8 mg/min dose and induced significant anxiety compared with placebo. We observed moderate acute tolerance to acute effects of DMT. In the self-guided titration session, the participants opted for moderate to strong psychedelic effects, comparable in intensity to the 1.8 mg/min DMT dose rate in the randomized dosing sessions. These results may assist with dose finding for future DMT research and demonstrate that acute subjective effects of DMT can be rapidly adjusted through dose titration.

Classification Schemes of Altered States of Consciousness

In recent years, there has been a renewed interest in the conceptual and empirical study of altered states of consciousness (ASCs) induced pharmacologically or otherwise, driven by their potential clinical applications. To draw attention to the rich history of research in this domain, we review prominent classification schemes that have been proposed to introduce systematicity in the scientific study of ASCs. The reviewed ASC classification schemes fall into three groups according to the criteria they use for categorization: (1) based on the nature, variety, and intensity of subjective experiences (state-based), including conceptual descriptions and psychometric assessments, (2) based on the technique of induction (method-based), and (3) descriptions of neurophysiological mechanisms of ASCs (neuro/physio-based). By comparing and extending existing classification schemes, we can enhance efforts to identify neural correlates of consciousness, particularly when examining mechanisms of ASC induction and the resulting subjective experience. Furthermore, an overview of what defining ASC characteristics different authors have proposed can inform future research in the conceptualization and quantification of ASC subjective effects, including the identification of those that might be relevant in clinical research. This review concludes by clustering the concepts from the state-based schemes, which are suggested for classifying ASC experiences. The resulting clusters can inspire future approaches to formulate and quantify the core phenomenology of ASC experiences to assist in basic and clinical research.

A systematic study of changes in monoamine neurotransmitters in the rat brain following acute administration of alpha-methyltryptamine (AMT), 5-methoxy-alpha-methyltryptamine (5-MeO-AMT) and 5-methoxy-N,N-diisopropyltryptamine (5-MeO-DiPT)

Alpha-methyltryptamine (AMT), 5-methoxy-alpha-methyltryptamine (5-MeO-AMT), and 5-methoxy-N,N-diisopropyltryptamine (5-MeO-DiPT) are three synthetic tryptamines with hallucinogenic properties that are widely abused worldwide. The hallucinogenic effects of tryptamines are primarily related to activation of the 5-HT receptor, and among the many subtypes of 5-HT receptors, the 5-HT2A receptor is the key receptor for hallucinogenic effects. In the present study, the monoamine neurotransmitters DA and its metabolites 3,4-Dihydroxyphenylacetic Acid (DOPAC) and homovanillic acid (HVA), 5-HT and its metabolite 5-hydroxyindoleacetic acid (5-HIAA) were systematically investigated in the prefrontal cortex (PFC), nucleus accumbent (NAc), dorsolateral striatum (DLS) and hippocampus (HIP) using a validated HPLC-ECD analytical method after administration of the three tryptamines at different doses. The results showed that the three tryptamines had certain effects and the effects were different in different brain regions and showed that AMT, 5-MeO-AMT and 5-MeO-DiPT had significant effects on monoaminergic neurotransmitters in rat brains. Among them, DAergic and serotonergic play important roles, and this study provides valuable information for further research on the neurochemical effects of tryptamine hallucinogens in the brain.

Pharmacokinetics and pharmacodynamics of sublingual microdosed lysergic acid diethylamide in healthy adult volunteers

INTRODUCTION

Microdosing is the practice of taking psychedelic drugs at doses that produce no or minimal perceptible subjective or behavioural effects. This study investigated the pharmacokinetics and pharmacodynamics of microdosed lysergic acid diethylamide (LSD).

METHODS

This was a Phase 1 double-blind placebo-controlled parallel-groups trial with 80 healthy male volunteers (four withdrawals due to anxiety). Plasma samples were taken at 0.5, 1, 2, 4 and 6 h after 10 µg sublingual LSD and analysed with liquid chromatography-tandem mass spectrometry (LC-MS/MS). LSD pharmacokinetics were modelled. Population analyses were performed using nonlinear mixed effects models. Heart rate and a visual analogue scale ('feel effect') were used to describe LSD pharmacodynamics. The effect of the relevant cytochrome P450 (CYP) genotype on LSD pharmacokinetics was qualitatively assessed. Plasma and serum levels of brain-derived neurotrophic factor (BDNF) were evaluated.

RESULTS

A one-compartment model best described LSD pharmacokinetics. Mean (95% confidence interval): elimination clearance = 7.78 L/h/70 kg (6.75-8.77), central volume of distribution = 32.9 L/70 kg (30.1, 36.0). Maximal concentration (0.20 µg/L), time to maximal concentration (1.51 h) and elimination half-life (3.08 h). The maximal increase in heart rate and visual analogue scale was small (<15%) compared to baseline estimates limiting the modelling. Two of the participants withdrawn from the study due to anxiety had intermediate-weak CYP2D6 activity. CYP2D6, CYP1A6, CYP2B6 and CYP2C9 qualitatively appeared to influence concentration. No evidence of alterations of peripheral BDNF with microdosing was found.

CONCLUSION

This study provides a population pharmacokinetic model and LC-MS/MS assay that can inform clinical and bioequivalence studies. Relevant CYP genotypes should be studied in larger samples as combined potential biomarkers of response. Microdose-sensitive and reliable pharmacodynamic measures are needed.

Network control energy reductions under DMT relate to serotonin receptors, signal diversity, and subjective experience

Psychedelics offer a profound window into the human brain through their robust effects on perception, subjective experience, and brain activity patterns. The serotonergic psychedelic N,N-dimethyltryptamine (DMT) induces a profoundly immersive altered state of consciousness lasting under 20 min, allowing the entire experience to be captured during a single functional magnetic resonance imaging (fMRI) scan. Using network control theory, we map energy trajectories of 14 individuals undergoing fMRI during DMT and placebo. We find that global control energy is reduced after DMT injection compared to placebo. Longitudinal trajectories of global control energy correlate with longitudinal trajectories of electroencephalography (EEG) signal diversity (a measure of entropy) and subjective drug intensity ratings. At the regional level, spatial patterns of DMT's effects on these metrics correlate with serotonin 2a receptor density from positron emission tomography (PET) data. Using receptor distribution and pharmacokinetic information, we recapitulate DMT's effects on global control energy trajectories, demonstrating control models can predict pharmacological effects on brain dynamics.

The evolution of N, N-Dimethyltryptamine: from metabolic pathways to brain connectivity

RATIONALE

N, N-Dimethyltryptamine (DMT), a potent serotonergic psychedelic, bridges ancient wisdom and modern science. The mechanisms underlying its powerful psychedelic effects and out-of-body experiences continue to intrigue scientists. The functional role of DMT remains ambiguous. This paper explores the endogenous presence of DMT in the human body and its diverse neuroregulatory functions, which influence hierarchical brain connectivity, and the mechanisms driving its psychedelic effects.

OBJECTIVE

This paper aims to analyze DMT-receptor binding, its effects on neuronal modulation, brain oscillations, and connectivity, and its influence on hallucinations, out-of-body experiences, and cognitive functions.

RESULTS

DMT administration induces significant changes in brain wave dynamics, including reduced alpha power, increased delta power, and heightened Lempel-Ziv complexity, reflecting enhanced neural signal diversity. Functional neuroimaging studies reveal that DMT enhances global functional connectivity (GFC), particularly in transmodal association cortices such as the salience network, frontoparietal network, and default mode network, correlating with ego dissolution. The receptor density-dependent effects of DMT were mapped to brain regions rich in serotonin 5-HT2A receptors, supporting its role in modulating consciousness and neuroplasticity.

CONCLUSION

This integrated analysis provides insights into the profound effects of DMT on human cognition, and consciousness, and its role in enhancing natural well-being. As we uncover the endogenous functions of DMT, it becomes clear that the study of its biology reveals a complex interplay between brain chemistry and consciousness.

Psilocybin therapy for mood dysfunction in Parkinson's disease: an open-label pilot trial

Mood dysfunction is highly prevalent in Parkinson's disease (PD), a main predictor of functional decline, and difficult to treat-novel interventions are critically needed. Psilocybin shows early promise for treating depression and anxiety, but its potential in PD is unknown, as safety concerns have excluded people with neurodegenerative disease from previous trials. In this open-label pilot (NCT04932434), we examined the feasibility of psilocybin therapy among people with mild to moderate stage PD plus depression and/or anxiety. 12 participants (mean age 63.2 ± 8.2 years, 5 women) received psilocybin (one 10 mg followed by one 25 mg dose) with psychotherapy. There were no serious adverse events, no medical interventions required to manage effects of psilocybin, and no exacerbation of psychosis. Ten participants experienced treatment-emergent adverse events; the most frequent were anxiety, nausea, and increased blood pressure. We observed no worsening of PD symptomology measured by the Movement Disorder Society Unified Parkinson's Disease Rating Scale (MDS-UPDRS). On the contrary, non-motor (MDS-UPDRS Part I: -13.8 ± 1.3, p < 0.001, Hedges' g = 3.0) and motor symptoms (Part II: -7.5 ± 0.9, p < 0.001, g = 1.2; Part III: -4.6 ± 1.3, p = 0.001; g = 0.3) as well as performance in select cognitive domains (Paired Associates Learning [-0.44 ± 0.14, p = .003, g = 0.4], Spatial Working Memory [-0.52 ± 0.17, p = 0.003, g = 0.7], and Probabilistic Reversal Learning [2.9 ± 0.9, p = 0.003, g = 1.3]) improved post-treatment, and improvements were sustained until the final safety assessment one month following drug exposure. Baseline Montgomery-Asberg Depression Rating Scale (MADRS) and Hamilton Anxiety Rating Scale (HAM-A) scores were 21.0 ± 8.7 and 17.0 ± 3.7, respectively. Both improved to a clinically meaningful degree post-treatment; these improvements persisted to the final assessment three months following drug exposure (MADRS: -9.3 ± 2.7, p = .001, g = 1.0; HAM-A: -3.8 ± 1.7; p = 0.031, g = 0.7). This study provides the first data on psilocybin's effects in any neurodegenerative disease. Results suggest that psilocybin therapy in PD warrants further investigation.

Behavioral effects of three synthetic tryptamine derivatives in rodents

AIMS

New synthetic tryptamine derivatives have emerged in the underground market. They act on serotonin receptors mimicking the effects of hallucinogenic drugs such as DOM. The DEA has identified three tryptamine derivatives of concern, 5-MeO-DBT, 5-Cl-DMT, and 4-OH-MiPT.

METHODS

Swiss Webster mice were tested for locomotor activity. Discriminative stimulus effects were tested in male Sprague-Dawley rats trained to discriminate DOM (0.5 mg/kg, 30-min pretreatment) from vehicle (0.9% saline).

RESULTS

In the locomotor activity tests, DOM (ED50 = 4.8 mg/kg) produced a 40-100-min depressant phase. 5-MeO-DBT (ID50 = 16.5 mg/kg; ED50 = 0.074 mg/kg) had a 50-min depressant phase and a 100-min stimulant phase. 5-Cl-DMT (ID50 = 12.3 mg/kg; ED50 = 6.1 mg/kg) produced a 20-40-min depressant phase and a 30-min stimulant phase. 4-OH-MiPT (ID50 = 5.8 mg/kg; ED50 = 0.6 mg/kg) had a 30-130-min depressant phase and a 50-minute stimulant phase. In the drug discrimination assay, 4-OH-MIPT (ED50 = 0.77 mg/kg) was fully substituted, whereas 5-Cl-DMT partially substituted for the discriminative stimulus effects produced by DOM (ED50 = 0.23 mg/kg). 5-MeO-DBT failed to substitute for the discriminative stimulus of DOM. 5-CL-DMT and 5-MeO-DBT decreased response rate.

CONCLUSION

The locomotor depressant effects of the three synthetic tryptamine derivatives were similar to DOM, but not as potent. In the drug discrimination assay, only 4-OH-MIPT was substituted fully for DOM. These results support the possibility that 4-OH-MIPT has abuse liability similar to DOM, whereas 5-MeO-DBT and 5-Cl-DMT may not.

The effect of low-dose psilocybin on brain neurotransmission and rat behavior

Psilocybin has various therapeutic effects in mental and psychological disorders, including depression and mood disorders, obsessive-compulsive disorders, substance addiction and anxiety. Pharmacodynamic properties of psilocybin depend on doses used and time after administration. The psilocybin dose range varies depending on whether it is used therapeutically or for recreational purposes in humans, but most animal studies require larger doses to induce an effect on brain neurotransmission and animal behavior. The aim of this study was to investigate the effect of psilocybin on the release of cortical neurotransmitters and rat behavior when it was administered subcutaneously at doses of 0.1, 0.3 and 0.6 mg/kg. Psilocybin affected the release of dopamine, noradrenaline, serotonin and acetylcholine in the frontal cortex as measured by microdialysis in freely moving rats. Psilocybin increased the release of aminergic transmitters in a non-linear manner with the dose of 0.3 mg/kg being the weakest. Psilocybin also increased the release of γ-aminobutyric acid, but glutamate release was enhanced only for the first 2 h after drug injection and was followed by a decrease for the rest of the experimental period. In contrast to 25I-NBOMe, an agonist of 5-HT2A receptors, psilocybin did not produce hallucinogenic activity expressed as wet dog shakes and did not disrupt sensorimotor gating in the acoustic startle response test. Furthermore, psilocybin showed anxiolytic effect in the light dark box test 1 h after administration. It also modulated the hypothalamic-pituitary-adrenal axis activity as it transiently increased serum corticosterone level, decreased serotonin, but increased dopamine turnover rates in the hypothalamus and inhibited the content of noradrenaline and adrenaline in the adrenal glands. The changes in the neurotransmitter release seem to play a role in psilocybin behavioral effects. The lack of hallucinogenic activity and disruptive effect on sensorimotor gating by psilocybin lower doses indicates that psychotomimetic effects did not occur. Psilocybin in contrast to 25I-NBOMe, ketamine and MDMA did not produce oxidative damage of DNA in the frontal cortex and hippocampus. Thus, the single low doses of psilocybin may have some beneficial properties and fewer harmful effects.

Large-scale brain connectivity changes following the administration of lysergic acid diethylamide, d-amphetamine, and 3,4-methylenedioxyamphetamine

Psychedelics have recently attracted significant attention for their potential to mitigate symptoms associated with various psychiatric disorders. However, the precise neurobiological mechanisms responsible for these effects remain incompletely understood. A valuable approach to gaining insights into the specific mechanisms of action involves comparing psychedelics with substances that have partially overlapping neurophysiological effects, i.e., modulating the same neurotransmitter systems. Imaging data were obtained from the clinical trial NCT03019822, which explored the acute effects of lysergic acid diethylamide (LSD), d-amphetamine, and 3,4-methylenedioxymethamphetamine (MDMA) in 28 healthy volunteers. The clinical trial employed a double-blind, placebo-controlled, crossover design. Herein, various resting-state connectivity measures were examined, including within-network connectivity (integrity), between-network connectivity (segregation), seed-based connectivity of resting-state networks, and global connectivity. Differences between placebo and the active conditions were assessed using repeated-measures ANOVA, followed by post-hoc pairwise t-tests. Changes in voxel-wise seed-based connectivity were correlated with serotonin 2 A receptor density maps. Compared to placebo, all substances reduced integrity in several networks, indicating both common and unique effects. While LSD uniquely reduced integrity in the default-mode network (DMN), the amphetamines, in contrast to our expectations, reduced integrity in more networks than LSD. However, LSD exhibited more pronounced segregation effects, characterized solely by decreases, in contrast to the amphetamines, which also induced increases. Across all substances, seed-based connectivity mostly increased between networks, with LSD demonstrating more pronounced effects than both amphetamines. Finally, while all substances decreased global connectivity in visual areas, compared to placebo, LSD specifically increased global connectivity in the basal ganglia and thalamus. These findings advance our understanding of the distinctive neurobiological effects of psychedelics, prompting further exploration of their therapeutic potential.

LPS-Induced Liver Inflammation Is Inhibited by Psilocybin and Eugenol in Mice

Background/Objectives: Liver inflammatory diseases are a major global health burden and are often exacerbated by inflammation driven by lipopolysaccharides (LPS) through toll-like receptor 4 signaling. This study evaluates the anti-inflammatory effects of psilocybin and eugenol in an LPS-induced liver inflammation model in C57BL/6J mice. Methods: Mice were treated with psilocybin (0.88 mg/kg) and/or eugenol (17.59 mg/kg) either before (pre-treatment) or after (post-treatment) LPS injection. Results: Psilocybin and eugenol, individually and in combination, significantly reduced the LPS-induced mRNA levels of pro-inflammatory cytokines, with post-treatment administration exhibiting stronger effects than pre-treatment. Psilocybin alone displayed the most pronounced anti-inflammatory response, especially for IL-1β, IL-6, and MCP-1, while its combination with eugenol in 1:50 ratio demonstrated similar results, with strongly reduced COX-2 and TNF-α. Histological analysis revealed improved nuclear circularity and reduced inflammatory infiltration in the treatment groups. Eugenol alone showed potential adverse effects, including increased MCP-1 and GM-CSF, but this was mitigated by the co-administration of psilocybin. Conclusions: These findings highlight psilocybin and its combination with eugenol as promising therapies for hepatic inflammation, suggesting their application in treating acute and chronic liver diseases. Future research should explore their long-term effects, the mechanisms underlying their anti-inflammatory actions, and their therapeutic efficacy in humans.

Extraction Yields of Psilocybin and Psilocin: A Short Review of Current Methods and Their Implications

The growing body of evidence supporting the therapeutic efficacy of psychoactive substances, like psilocybin, has driven significant interest in recent decades due to their low toxicity and potential applications in treating various mental health disorders. However, producing pharmaceutical-grade psilocybin remains challenging, with three primary approaches: chemical synthesis, biosynthesis, and extraction from Psilocybe mushroom fruiting bodies. This systematic review evaluates the extraction and quantification methods for psilocybin and psilocin, aiming to contribute to the development of standardized protocols that ensure compound quality and purity. A total of 25 relevant studies were selected from an initial pool of 9152 publications indexed in platforms such as Scopus, ScienceDirect, Web of Science, and PubMed. The findings indicate that both the extraction method and the choice of mushroom species significantly influence compound yields. Ultrasonic bath extraction was identified as the most efficient technique, particularly for species including Psilocybe cyanescens and Psilocybe cubensis. High-performance liquid chromatography (HPLC) was the most-used method for identifying and quantifying these compounds. Furthermore, polar solvents were critical for effective solubilization, with parameters such as temperature, solvent-to-material ratio, and extraction time playing key roles in optimizing yields. This review serves as a key scientific reference for advancing research, enhancing analytical precision, and ensuring reproducibility through the standardization of extraction and quantification protocols.

Dimethyltryptamine (DMT) and ibogaine elicit membrane effects in HEK cells transiently transfected with the human 5-HT2A receptor

Psychedelics show promise in treating psychiatric disorders. Therapeutic effects appear to involve activation of the 5-Hydroxytryptamine 2A receptor (5-HT2AR), a G protein-coupled receptor (GPCR). Several SNPs of the 5-HT2AR naturally occur, which are associated with differences in receptor function and altered responsiveness to treatments. New compounds suspected to act at the 5-HT2AR are actively being generated. HEK cells are not commonly used to study membrane effects induced by agonists of GPCRs. In this study, for the first time, membrane actions of two psychedelics, dimethyltryptamine (DMT) and ibogaine on HEK cells transiently transfected with either the human wildtype (WT) or the human I197V mutated 5-HT2AR were investigated using whole-cell electrophysiology. Membrane effects were observed in both genotypes and with both drugs in most cells, while no responses were observed in non-transfected HEK cells suggesting that responses were due to 5-HT2AR activation. In HEK cells transfected with the I197V SNP, a significantly shorter duration of the DMT response was observed, however there were no differences in drug-elicited amplitudes between drug or receptor genotype. I-V curves showed a significant effect of drug exposure for both DMT and ibogaine at the highest concentration evaluated. Taken together, our data show transfection of the 5-HT2AR, a GPCR, in HEK cells is able to activate downstream ion channels following exposure to two different 5-HT2AR agonists. Accordingly, investigations of novel compounds suspected to act at 5-HT2ARs can include examination of elicitation of ionic currents in 5-HT2AR transfected HEK cells, and drug effects at SNPs can also be evaluated.

Neurochemical and Neurophysiological Effects of Intravenous Administration of N,N-Dimethyltryptamine in Rats

N,N-dimethyltryptamine (DMT) is a serotonergic psychedelic that is being investigated clinically for the treatment of psychiatric disorders. Although the neurophysiological effects of DMT in humans are well-characterized, similar studies in animal models as well as data on the neurochemical effects of DMT are generally lacking, which are critical for mechanistic understanding. In the current study, we combined behavioral analysis, high-density (32-channel) electroencephalography, and ultra-high-performance liquid chromatography-tandem mass spectrometry to simultaneously quantify changes in behavior, cortical neural dynamics, and levels of 17 neurochemicals in medial prefrontal and somatosensory cortices before, during, and after intravenous administration of three different doses of DMT (0.75 mg/kg, 3.75 mg/kg, 7.5 mg/kg) in male and female adult rats. All three doses of DMT produced head twitch response with most twitches observed after the low dose. DMT caused dose-dependent increases in serotonin and dopamine levels in both cortical sites along with a reduction in EEG spectral power in theta (4-10 Hz) and low gamma (25-55 Hz), and increase in power in delta (1-4 Hz), medium gamma (65-115 ), and high gamma (125-155 Hz) bands. Functional connectivity decreased in the delta band and increased across the gamma bands. In addition, we provide the first measurements of endogenous DMT in these cortical sites at levels comparable to serotonin and dopamine, which together with a previous study in occipital cortex, suggests a physiological role for endogenous DMT. This study represents one of the most comprehensive characterizations of psychedelic drug action in rats and the first to be conducted with DMT.

Significance Statement

N,N-dimethyltryptamine (DMT) is a serotonergic psychedelic with potential as a tool for probing the neurobiology of consciousness and as a therapeutic agent for psychiatric disorders. However, the neurochemical and neurophysiological effects of DMT in rat, a preferred animal model for mechanistic studies, are unclear. We demonstrate that intravenous DMT caused a dose-dependent increase in serotonin and dopamine in medial prefrontal and somatosensory cortices, and simultaneously increased gamma functional connectivity. Similar effects have been shown for other serotonergic and atypical psychedelics, suggesting a shared mechanism of drug action. Additionally, we report DMT during normal wakefulness in two spatially and functionally distinct cortical sites - prefrontal, somatosensory - at levels comparable to those of serotonin and dopamine, supporting a physiological role for endogenous DMT.

Evaluating the value and risks of psychedelics for psychiatric medicine: a clinical perspective

INTRODUCTION

After a long period of obscurantism, a possible role of psychedelics in clinical practice has progressively become a tangible perspective during the last two decades. However, the resounding enthusiasm linked to such 'psychedelic renaissance' runs the risk to unduly minimize the possible hazards associated with these compounds, while expanding their alleged benefits to improbable panacea-like proportions. In order to avoid mystifying or demonizing the properties of 5-HT2a agonists on emotional grounds, this subject requires a strictly unprejudiced and cautious approach to the evidence.

AREAS COVERED

In this article, the authors attempted to comprehensively analyze the available literature to provide a balanced overview of the possible benefits of psychedelics in healthcare, taking into account their potential risks.

EXPERT OPINION

To date, psychedelics have shown a therapeutic potential in a wide range of conditions, with a seemingly limited risk of inducing adverse reactions, including abuse and dependence, when administered in a controlled environment by specialized personnel. In any case, although several questions remain unanswered before drawing firm conclusions, further studies are needed to establish which conditions and subjects could benefit from psychedelics and which patients bear the greater risk of adversities.

Psychedelics and schizophrenia: a double-edged sword

Psychedelics have shown promising effects in several psychiatric diseases as demonstrated by multiple clinical trials. However, no clinical experiments on patients with schizophrenia have been conducted up to date, except for some old semi-anecdotal studies mainly performed in the time-span '50s-'60s. Notably, these studies reported interesting findings, particularly on the improvement of negative symptoms and social cognition. With no doubts the lack of modern clinical studies is due to the psychomimetic properties of psychedelics, a noteworthy downside that could worsen positive symptoms. However, a rapidly increasing body of evidence has suggested that the mechanisms of action of such compounds partially overlaps with the pathogenic underpinnings of schizophrenia but in an opposite way. These findings suggest that, despite being a controversial issue, the use of psychedelics in the treatment of schizophrenia would be based on a strong biological rationale. Therefore, the aim of our perspective paper is to provide a background on the old experiments with psychedelics performed on patients with schizophrenia, interpreting them in the light of recent molecular findings on their ability to induce neuroplasticity and modulate connectivity, the immune and TAARs systems, neurotransmitters, and neurotropic factors. No systematic approach was adopted in reviewing the evidence given the difficulty to retrieve and interpret old findings. Interestingly, we identified a therapeutic potential of psychedelics in schizophrenia adopting a critical point of view, particularly on negative symptoms and social cognition, and we summarized all the relevant findings. We also identified an eligible subpopulation of chronic patients predominantly burdened by negative symptoms, outlining possible therapeutic strategies which encompass very low doses of psychedelics (microdosing), carefully considering safety and feasibility, to pave the way to future clinical trials.

Cardiovascular effects and safety of classic psychedelics

Psychedelics, used for millennia in spiritual and healing practices, have emerged as promising treatments for mental health conditions including depression, post-traumatic stress disorder (PTSD), substance use disorders and anxiety. Despite the therapeutic potential of psychedelics and their increasing use in both medical and nonmedical settings, there is a paucity of data on their cardiovascular safety. Here we review current evidence on the cardiovascular effects and safety of this unique class of therapeutic agents. The cardiovascular effects and associated risks of classic psychedelics are categorized into three areas: electrophysiological effects and arrhythmia risk, structural effects and valvular heart disease risk, and vascular effects including hypertension and ischemia risks. The Review also emphasizes crucial knowledge gaps that require further basic and clinical investigation including studies in individuals with underlying cardiovascular disease, characterization of important drug-drug interactions and studies on the safety of repetitive, long-term (including microdosing) exposure to classic psychedelics.

A highly sensitive UHPLC-MS/MS method for determining 15 designer LSD analogs in biological samples with application to stability studies

In recent years, the rise in the synthesis and distribution of LSD analogs in illicit drug markets, commonly referred to as "designer psychedelics", has contributed to increased recreational use. This trend has resulted in a rising number of global reports, with law enforcement increasingly detecting these compounds in blotter papers and biological samples. In the presented paper, an UHPLC-QqQ-MS/MS method was developed for trace determination (fg mL-1) of LSD, its designer analogs (ALD-52, AL-LAD, LAMPA, LSM-775, LSZ, MiPLA, 1B-LSD, 1cP-LSD, 1cP-MiPLA, 1P-LSD, 1P-MiPLA, 1V-LSD and 2-Bromo-LSD) and its metabolite (2-oxo-3-OH-LSD) with simultaneous separation of structural isomers. Biological samples were prepared using liquid-liquid extraction (LLE) at pH 9 (with ethyl acetate); quantification was performed in multiple reaction monitoring (MRM) mode. LSD-d3 was used as an internal standard. The limit of quantification (LOQ) for all substances was 0.5 pg mL-1. Precision and accuracy did not exceed 15.8% and ±14.4%, respectively. Recovery and matrix effect values were 80.6-118.6% and ±19.4%. A stability study was conducted over 30 days under different storage conditions (25 °C, 4 °C and -20 °C) for blood, urine, plasma, and serum, collected in various test tube configurations and with different preservative agents. It was found that the collection of samples in NaF can effectively stabilize LSD analogs and minimize the conversion of N1-substituted compounds to LSD or MiPLA. The presented method is the most sensitive to date for analyzing designer LSD analogs in biological samples, with potential for routine clinical and forensic use, enhancing detection of emerging illicit compounds. By examining the mass spectra (QTOF-MS/MS) obtained in this study and reviewing the literature on analytical characterization of LSD analogs, we proposed fragmentation patterns to aid in future identification of new designer LSD analogs (NPS).

Clinical and preclinical evidence of psilocybin as antidepressant. A narrative review

In the rapidly growing field of psychedelic research, psilocybin (and active metabolite psilocin) has been proposed as a promising candidate in the search for novel treatments for neuropsychiatric disorders. Clinical trials have revealed that psilocybin has a large, rapid, and persistent effect in the improvement of symptoms of depression and anxiety. The safety profile is considered favourable, with low toxicity and good tolerance. Several preclinical studies have also been carried out to determine the long-term mechanism of action of this drug. In this sense, preclinical studies in naïve animals as well as in animal models of disease have shown somewhat discrepant results in conventional tests for assessment of depression- and anxiety-like phenotype in response to psilocybin, but overall suggest positive outcomes. Additionally, several valuable assays in rodent models have been developed over the years to elucidate the neurochemical correlates of serotonin 2A receptor (5HT2AR) activation in the brain, primary molecular target of psilocin. This review aims to provide a general overview of the current and most recent literature in the therapeutic potential of psilocybin through a description of clinical trials of psilocybin-assisted psychotherapy, and to showcase the scene in the up-to-date preclinical research. A detailed description of preclinical rodent models and experimental approaches that have been used to study the neurobiological and behavioural actions of psilocybin is provided, and potential therapeutic mechanisms of action are discussed.

Psychedelics for the Treatment of Psychiatric Disorders: Interpreting and Translating Available Evidence and Guidance for Future Research

During the past decade, there has been extraordinary public, media, and medical research interest in psychedelics as promising therapeutics for difficult-to-treat psychiatric disorders. Short-term controlled trial data suggest that certain psychedelics are effective and safe in the treatment of major depressive disorder, treatment-resistant depression, and posttraumatic stress disorder. Preliminary evidence also supports efficacy in other psychiatric disorders (e.g., tobacco and alcohol use disorders). Notwithstanding the interest and promise of psychedelics, concerns have arisen with respect to the interpretability and translatability of study results. For example, aspects related to short- and long-term safety, abuse liability, and the essentiality of the psychedelic "trip" and psychological support are, inter alia, insufficiently characterized with psychedelic agents. The overarching aims in this overview are 1) to review methodological aspects that affect inferences and interpretation of extant psychedelic studies in psychiatric disorders, and 2) to provide guidance for future research and development of psychedelic treatment in psychiatry, critical to study interpretation and clinical implementation.

Psilocybin reduces grooming in the SAPAP3 knockout mouse model of compulsive behaviour

Psilocybin is a serotonergic psychedelic compound which shows promise for treating compulsive behaviours. This is particularly pertinent as compulsive disorders require research into new pharmacological treatment options as the current frontline treatments such as selective serotonin reuptake inhibitors, require chronic administration, have significant side effects, and leave almost half of the clinical population refractory to treatment. In this study, we investigated psilocybin administration in male and female SAPAP3 knockout (KO) mice, a well-validated mouse model of obsessive compulsive and related disorders. We assessed the effects of acute psilocybin (1 mg/kg, intraperitoneal) administration on head twitch and locomotor behaviour as well as anxiety- and compulsive-like behaviours at multiple time-points (1, 3 and 8 days post-injection). While psilocybin did not have any effect on anxiety-like behaviours, we revealed that acute psilocybin administration led to enduring reductions in compulsive behaviour in male SAPAP3 KO mice and reduced grooming behaviour in female wild-type (WT) and SAPAP3 KO mice. We also found that psilocybin increased locomotion in WT littermates but not in SAPAP3 KO mice, suggesting in vivo serotonergic dysfunctions in KO animals. On the other hand, the typical head-twitch response following acute psilocybin (confirming its hallucinogenic-like effect at this dose) was observed in both genotypes. Our novel findings suggest that acute psilocybin may have potential to reduce compulsive-like behaviours (up to 1 week after a single injection). Our study can inform future research directions as well as supporting the utility of psilocybin as a novel treatment option for compulsive disorders.

Serotonin 1A Receptors Modulate Serotonin 2A Receptor-Mediated Behavioral Effects of 5-Methoxy-N,N-dimethyltryptamine Analogs in Mice

5-methoxy-N,N-dimethyltrytpamine (5-MeO-DMT) analogs are used as recreational drugs, but they are also being developed as potential medicines, warranting further investigation into their pharmacology. Here, we investigated the neuropharmacology of 5-MeO-DMT and several of its N-alkyl, N-allyl, and 2-methyl analogs, with three major aims: 1) to determine in vitro receptor profiles for the compounds, 2) to characterize in vitro functional activities at serotonin (5-HT) 2A receptors (5-HT2A) and 1A receptors (5-HT1A), and 3) to examine the influence of 5-HT1A on 5-HT2A-mediated psychedelic-like effects in the mouse head twitch response (HTR) model. In vitro receptor binding and functional assays showed that all 5-MeO-DMT analogs bind with high affinity and activate multiple targets (e.g., 5-HT receptor subtypes, alpha adrenergic receptors), including potent effects at 5-HT2A and 5-HT1A. In C57Bl/6J mice, subcutaneous injection of the analogs induced HTRs with varying potencies (ED50 range = 0.2-1.8 mg/kg) and maximal effects (Emax range = 20-60 HTRs/30 min), while inducing hypothermia and hypolocomotion at higher doses (ED50 range = 3.2-20.6 mg/kg). 5-HT2A antagonist pretreatment blocked drug-induced HTRs, whereas 5-HT1A antagonist pretreatment enhanced HTRs. In general, N,N-dialkyl and N-isopropyl derivatives displayed HTR activity, while the N-methyl, N-ethyl, and 2-methyl analogs did not. Importantly, blockade of 5-HT1A unmasked latent HTR activity for the N-ethyl analog and markedly increased maximal responses for other HTR-active compounds (40-90 HTRs/30 min), supporting the notion that 5-HT1A agonist activity can dampen 5-HT2A-mediated HTRs. Suppression of 5-HT2A-mediated HTRs by 5-HT1A only occurred after high 5-MeO-DMT doses, suggesting involvement of other receptors in modulating psychedelic-like effects. Overall, our findings provide key information about the receptor target profiles for 5-MeO-DMT analogs, the structure-activity relationships for inducing psychedelic-like effects, and the critical role of 5-HT1A agonism in modulating acute psychoactive effects of 5-HT2A agonists.

Synergistic, multi-level understanding of psychedelics: three systematic reviews and meta-analyses of their pharmacology, neuroimaging and phenomenology

Serotonergic psychedelics induce altered states of consciousness and have shown potential for treating a variety of neuropsychiatric disorders, including depression and addiction. Yet their modes of action are not fully understood. Here, we provide a novel, synergistic understanding of psychedelics arising from systematic reviews and meta-analyses of three hierarchical levels of analysis: (1) subjective experience (phenomenology), (2) neuroimaging and (3) molecular pharmacology. Phenomenologically, medium and high doses of LSD yield significantly higher ratings of visionary restructuralisation than psilocybin on the 5-dimensional Altered States of Consciousness Scale. Our neuroimaging results reveal that, in general, psychedelics significantly strengthen between-network functional connectivity (FC) while significantly diminishing within-network FC. Pharmacologically, LSD induces significantly more inositol phosphate formation at the 5-HT2A receptor than DMT and psilocin, yet there are no significant between-drug differences in the selectivity of psychedelics for the 5-HT2A, 5-HT2C, or D2 receptors, relative to the 5-HT1A receptor. Our meta-analyses link DMT, LSD, and psilocybin to specific neural fingerprints at each level of analysis. The results show a highly non-linear relationship between these fingerprints. Overall, our analysis highlighted the high heterogeneity and risk of bias in the literature. This suggests an urgent need for standardising experimental procedures and analysis techniques, as well as for more research on the emergence between different levels of psychedelic effects.

Mescaline-induced behavioral alterations are mediated by 5-HT2A and 5-HT2C receptors in rats

RATIONALE

Mescaline is a classical psychedelic compound with a phenylethylamine structure that primarily acts on serotonin 5-HT2A/C receptors, but also binds to 5-HT1A and 5-HT2B receptors. Despite being the first psychedelic ever isolated and synthesized, the precise role of different serotonin receptor subtypes in its behavioral pharmacology is not fully understood.

OBJECTIVES

In this study, we aimed to investigate how selective antagonists of 5-HT2A, 5-HT2B, 5-HT2C, and 5-HT1A receptors affect the behavioral changes induced by subcutaneous administration of mescaline (at doses of 10, 20, and 100 mg/kg) in rats.

METHODS

We used adult male Wistar rats in all our experiments. We evaluated locomotor activity using the open field test, and assessed sensorimotor gating deficits by measuring prepulse inhibition (PPI) of acoustic startle reaction (ASR).

RESULTS

While the highest dose of mescaline induced hyperlocomotion (p < 0.001), which almost all the other antagonists reversed (p < 0.05-0.001), the PPI deficits were selectively normalized by the 5-HT2A antagonist (p < 0.05-0.01). The 5-HT2C antagonist partially reversed the small PPI deficit induced by lower doses of mescaline (p = 0.0017).

CONCLUSION

Our findings suggest that mescaline-induced changes in behavior are primarily mediated by the 5-HT2A receptor subtype, with less pronounced contributions from the 5-HT2C receptor. The other antagonists had limited effects.

Metabolite markers for three synthetic tryptamines N-ethyl-N-propyltryptamine, 4-hydroxy-N-ethyl-N-propyltryptamine, and 5-methoxy-N-ethyl-N-propyltryptamine

N-Ethyl-N-propyltryptamine (EPT), 4-hydroxy-N-ethyl-N-propyltryptamine (4-OH-EPT), and 5-methoxy-N-ethyl-N-propyltryptamine (5-MeO-EPT) are new psychoactive substances classified as tryptamines, sold online. Many tryptamines metabolize rapidly, and identifying the appropriate metabolites to reveal intake is essential. While the metabolism of 4-OH-EPT and 5-MeO-EPT are not previously described, EPT is known to form metabolites by indole ring hydroxylation among others. Based on general knowledge of metabolic patterns, 5-MeO-EPT is also expected to form ring hydroxylated EPT (5-OH-EPT). In the present study, the aim was to characterize the major metabolites of EPT, 4-OH-EPT, and 5-MeO-EPT, to provide markers for substance identification in forensic casework. The tryptamines were incubated with pooled human liver microsomes at 37°C for up to 4 h. The generated metabolites were separated and detected by ultra-high performance liquid chromatography-quadrupole time-of-flight mass spectrometry analysis. The major in vitro EPT metabolites were formed by hydroxylation, N-dealkylation, and carbonylation. In comparison, 4-OH-EPT metabolism was dominated by double bond formation, N-dealkylation, hydroxylation, and carbonylation in vitro and hydroxylation or carbonylation combined with double bond loss, carbonylation, N-dealkylation, and hydroxylation in vivo. 5-MeO-EPT was metabolized by O-demethylation, hydroxylation, and N-dealkylation in vitro. The usefulness of the characterized metabolites in forensic casework was demonstrated by identification of unique metabolites for 4-OH-EPT in a human postmortem blood sample with suspected EPT or 4-OH-EPT intoxication.

Psychedelics: A review of their effects on recalled aversive memories and fear/anxiety expression in rodents

Threatening events and stressful experiences can lead to maladaptive memories and related behaviors. Existing treatments often fail to address these issues linked to anxiety/stress-related disorders effectively. This review identifies dose ranges associated with specific actions across various psychedelics. We examined psilocybin/psilocin, lysergic acid diethylamide (LSD), N,N-dimethyltryptamine (DMT), mescaline, 5-methoxy-N,N-dimethyltryptamine (5-MeO-DMT), serotonin 2 A/2 C agonists (e.g., DOI) and 3,4-methylenedioxymethamphetamine (MDMA) on aversive memory extinction and reconsolidation, learned fear, anxiety, and locomotion in rodents. Nearly 400 studies published since 1957 were reviewed. Psychedelics often show biphasic effects on locomotion at doses that enhance extinction learning/retention, impair memory reconsolidation, or reduce learned fear and anxiety. Emerging evidence suggests a dissociation between their prospective benefits and locomotor effects. Under-explored aspects include sex differences, susceptibility to interference as memories age and generalize, repeated treatments, and immediate vs. delayed changes. Validating findings in traumatic-like memory and maladaptive fear/anxiety models is essential. Understanding how psychedelics modulate threat responses and post-retrieval memory processes in rodents may inform drug development and human studies, improving therapeutic approaches for related psychiatric conditions.

Psilocybin as a novel treatment for chronic pain

Psychedelic drugs are under active consideration for clinical use and have generated significant interest for their potential as anti-nociceptive treatments for chronic pain, and for addressing conditions like depression, frequently co-morbid with pain. This review primarily explores the utility of preclinical animal models in investigating the potential of psilocybin as an anti-nociceptive agent. Initial studies involving psilocybin in animal models of neuropathic and inflammatory pain are summarised, alongside areas where further research is needed. The potential mechanisms of action, including targeting serotonergic pathways through the activation of 5-HT2A receptors at both spinal and central levels, as well as neuroplastic actions that improve functional connectivity in brain regions involved in chronic pain, are considered. Current clinical aspects and the translational potential of psilocybin from animal models to chronic pain patients are reviewed. Also discussed is psilocybin's profile as an ideal anti-nociceptive agent, with a wide range of effects against chronic pain and its associated inflammatory or emotional components.

Safety pharmacology of acute mescaline administration in healthy participants

AIMS

Psychedelics, including mescaline, may serve as novel treatments for depression and anxiety. However, data is scarce on the safety of mescaline.

METHODS

The present pooled analysis included two double-blind, randomized, placebo-controlled studies with a total of 48 participants and 96 mescaline administrations. Single oral-dose administrations (n = 16/dose) of mescaline at doses of 100-800 mg were used. Acute subjective and autonomic effects and acute and subacute adverse effects were recorded. Liver and kidney function, blood cell counts, and "flashbacks" were documented at the end of the studies.

RESULTS

Positive subjective effects dose-dependently increased and were higher than negative subjective effects for all mescaline doses. Autonomic effects increased moderately. Systolic blood pressure remained < 180 mmHg in all participants. Of all mescaline administrations, diastolic blood pressure > 100 mmHg was measured in 6%, heart rate > 100 beats/min was measured in 3% and body temperature > 38 °C was measured in 5%. The total number of acute adverse effects was 51, 12, 179, 143, 165 and 180 at 100, 200, 300, 400, 500 and 800 mg doses of mescaline, respectively. Nausea was dose-limiting. Kidney and liver function and blood cell counts remained normal. "Flashbacks" were reported after 2% of all mescaline administrations.

CONCLUSIONS

These findings suggest that the administration of single mescaline doses up to 800 mg are safe in a controlled clinical setting with regard to acute psychological and physical harm in healthy participants.

Synthesis of Tryptamine-Thiazolidin-4-one Derivatives and the Combined In Silico and In Vitro Evaluation of their Biological Activity and Cytotoxicity

Tryptamine, a monoamine alkaloid with an indole ring structure, is derived from the decarboxylation of the amino acid tryptophan, which is present in fungi, plants, and animals. Tryptamine analogues hold significant therapeutic potential due to their broad pharmacological activities, including roles as neurotransmitters and potential therapeutic agents for various diseases. Structural modifications of tryptamine enhance receptor selectivity and metabolic stability, improving therapeutic efficacy. These modifications are crucial for optimizing pharmacokinetic and pharmacodynamic properties, making the analogues more effective and safer for clinical use. In this study, novel tryptamine-thiazolidin-4-one (YS1-12) derivatives were synthesized via a one-pot three-component condensation reaction. The synthesized compounds are characterized by different spectroscopy techniques such as FT-IR, 1H NMR, 13C NMR, and HR-NMS. The synthesized compounds were subjected to binary QSAR disease models for bioactivity prediction and a target prediction model for target analysis. Potential targets were identified, and physics-based molecular simulations were conducted. Additionally, MM/GBSA binding free energy analysis was performed to calculate the average binding free energies of YS1-12 compared to reference molecules. Our computational results indicated promising biological activities for these new compounds. To further investigate these activities, the compounds were tested in vitro using two different cancer cell lines: YKG-1 glioblastoma and SH-SY5Y neuroblastoma cells. The results confirmed the potential activities of these novel compounds. Notably, compounds YS4 and YS10 exhibited favorable activities compared to the control compounds 5-FU and Temozolomide. YS4 demonstrated an IC50 value of 20 nM against YKG-1 cells, while YS10 exhibited an IC50 value of 0.44 nM against SH-SY5Y cells.

Molecular and structural insights into the 5-HT2C receptor as a therapeutic target for substance use disorders

Substance use disorder (SUD) is a chronic condition, with maintained abuse of a substance leading to physiological and psychological alterations and often changes in cognitive and social behaviours. Current therapies include psychotherapy coupled with medication; however, high relapse rates reveal the shortcomings of these therapies. The signalling, expression profile, and neurological function of the serotonin 2C receptor (5-HT2C receptor) make it a candidate of interest for the treatment of SUD. Recently, psychedelics, which broadly act at 5-HT2 receptors, have indicated potential for the treatment of SUD, implicating the 5-HT2C receptor. The modern psychedelic movement has rekindled interest in the 5-HT2C receptor, resulting in many new studies, especially structural analyses. This review explores the structural, molecular and cellular mechanisms governing 5-HT2C receptor function in the context of SUD. This provides the basis of the preclinical and clinical evidence for their role in SUD and highlights the potential for future exploration.

Psilocin, the Psychoactive Metabolite of Psilocybin, Modulates Select Neuroimmune Functions of Microglial Cells in a 5-HT2 Receptor-Dependent Manner

Neuroinflammation that is caused by microglia, the main immune cells of the brain, contributes to neurodegenerative diseases. Psychedelics, including psilocybin and lysergic acid diethylamide (LSD), possess certain anti-inflammatory properties and, therefore, should be considered as drug candidates for treating neuroinflammatory pathologies. When ingested, psilocybin is rapidly dephosphorylated to yield psilocin, which crosses the blood-brain barrier and exerts psychotropic activity by interacting with the 5-hydroxytryptamine 2A receptors (5-HT2ARs) on neurons. Since microglia express all three 5-HT2R isoforms, we hypothesized that, by interacting with these receptors, psilocin beneficially modulates select neuroimmune functions of microglia. We used microglia-like cell lines to demonstrate that psilocin, at non-toxic concentrations, did not affect the secretion of tumor necrosis factor (TNF) by immune-stimulated microglial cells, but significantly inhibited their phagocytic activity, the release of reactive oxygen species (ROS), and nitric oxide (NO) production. The inhibitory activity of psilocin on the latter two functions was similar to that of two selective 5-HT2R agonists, namely, 25I-NBOH and Ro60-0175. The role of this subfamily of receptors was further demonstrated by the application of 5-HT2R antagonists cyproheptadine and risperidone. Psilocin should be considered a novel drug candidate that might be effective in treating neuroimmune disorders, such as neurodegenerative diseases, where reactive microglia are significant contributors.

Acute dose-dependent effects of mescaline in a double-blind placebo-controlled study in healthy subjects

Classic psychedelics have regained interest in research and therapy. Despite the long tradition of the human use of mescaline, modern data on its dose-dependent acute effects and pharmacokinetics are lacking. Additionally, its mechanism of action has not been investigated in humans. We used a randomized, double-blind, placebo-controlled, crossover design in 16 healthy subjects (8 women) who received placebo, mescaline (100, 200, 400, and 800 mg), and 800 mg mescaline together with the serotonin 5-hydroxytryptamine-2A (5-HT2A) receptor antagonist ketanserin (40 mg) to assess subjective effects, autonomic effects, adverse effects, and pharmacokinetics up to 30 h after drug administration. Mescaline at doses >100 mg induced dose-dependent acute subjective effects. Mescaline increased systolic and diastolic blood pressure at doses >100 mg, with no difference between doses of 200-800 mg. Heart rate increased dose-dependently. Pharmacokinetics of mescaline were dose-proportional. Maximal concentrations were reached after approximately 2 h, and the plasma elimination half-life was approximately 3.5 h. The average duration of subjective effects increased from 6.4 to 14 h with increasing doses of 100-800 mg mescaline. Nausea and emesis were frequent adverse effects at the 800 mg dose. Co-administration of ketanserin attenuated and shortened acute effects of 800 mg mescaline to become comparable to the 100 and 200 mg doses. There were no ceiling effects of the subjective response within the investigated dose range, but tolerability was lower at the highest doses. These results may assist with dose finding for future research and suggest that acute effects of mescaline are primarily mediated by 5-HT2A receptors.

Psilocybin increases optimistic engagement over time: computational modelling of behaviour in rats

Psilocybin has shown promise as a novel pharmacological intervention for treatment of depression, where post-acute effects of psilocybin treatment have been associated with increased positive mood and decreased pessimism. Although psilocybin is proving to be effective in clinical trials for treatment of psychiatric disorders, the information processing mechanisms affected by psilocybin are not well understood. Here, we fit active inference and reinforcement learning computational models to a novel two-armed bandit reversal learning task capable of capturing engagement behaviour in rats. The model revealed that after receiving psilocybin, rats achieve more rewards through increased task engagement, mediated by modification of forgetting rates and reduced loss aversion. These findings suggest that psilocybin may afford an optimism bias that arises through altered belief updating, with translational potential for clinical populations characterised by lack of optimism.

Psychedelics: From Cave Art to 21st-Century Medicine for Addiction

BACKGROUND

Psychedelic substance use in ritualistic and ceremonial settings dates back as early as 8,500 BCE. Only in recent years, from the mid-20th century, we have seen the re-emergence of psychedelics in a therapeutic setting and more specifically for the treatment of addiction. This article aims to review research over the past 40 years using classic (psilocybin, lysergic acid diethylamide [LSD], dimethyltryptamine [DMT], mescaline) and atypical (ketamine, ibogaine, 5-MeO-DMT, 3,4-methylenedioxymethamphetamine) psychedelics for the treatment of addiction.

SUMMARY

We will start with an overview of the pharmacology and physiological and psychological properties of psychedelic substances from pre-clinical and clinical research. We will then provide an overview of evidence gathered by studies conducted in controlled research environments and naturalistic and ceremonial settings, while we identify the proposed therapeutic mechanisms of each psychedelic substance.

KEY MESSAGES

Classic and atypical psychedelics show promise as therapeutic alternatives for the treatment of addiction, through the improvement of psychological and physiological symptoms of dependence. A more comprehensive understanding of the ancient and present-day knowledge of the therapeutic potential of psychedelics can facilitate hope for psychedelic therapeutics in the treatment of addiction, especially for individuals who have failed other conventional treatment methods.

Chemical Reactivity Parameters to Analyze Psychedelics: How Do We Explain the Potency of the Drugs?

Psychedelics are psychoactive substances that produce changes in thoughts and feelings and modifications in perceptions of reality. The most potent psychedelic is also the first semisynthetic hallucinogen (lysergic acid diethylamide). Psychedelics have been investigated for decades because of their potential therapeutic effects in the treatment of neuropsychiatric diseases and also because these drugs are useful in controlling addictions to other substances. In this investigation, we analyze 27 psychedelic molecules. These compounds are serotonergic psychedelics; that is, they are serotonin agonists. We analyze the electron transfer properties to better understand the mechanism of action of these substances. We found that the electron acceptance capacity is related to the potency of the drugs: the best electron acceptor is also the most potent drug. We also used global softness as a parameter of reactivity. Molecules with greater global softness are more polarizable and also have greater potency. These results are useful to continue our understanding of the mechanism of action of psychotropic drugs.

Rapid effects of tryptamine psychedelics on perceptual distortions and early visual cortical population receptive fields

N, N-dimethyltryptamine (DMT) is a psychedelic tryptamine acting on 5-HT2A serotonin receptors, which is associated with intense visual hallucinatory phenomena and perceptual changes such as distortions in visual space. The neural underpinnings of these effects remain unknown. We hypothesised that changes in population receptive field (pRF) properties in the primary visual cortex (V1) might underlie visual perceptual experience. We tested this hypothesis using magnetic resonance imaging (MRI) in a within-subject design. We used a technique called pRF mapping, which measures neural population visual response properties and retinotopic maps in early visual areas. We show that in the presence of visual effects, as documented by the Hallucinogen Rating Scale (HRS), the mean pRF sizes in V1 significantly increase in the peripheral visual field for active condition (inhaled DMT) compared to the control. Eye and head movement differences were absent across conditions. This evidence for short-term effects of DMT in pRF may explain perceptual distortions induced by psychedelics such as field blurring, tunnel vision (peripheral vision becoming blurred while central vision remains sharp) and the enlargement of nearby visual space, particularly at the visual locations surrounding the fovea. Our findings are also consistent with a mechanistic framework whereby gain control of ongoing and evoked activity in the visual cortex is controlled by activation of 5-HT2A receptors.

Structure-activity relationships of serotonergic 5-MeO-DMT derivatives: insights into psychoactive and thermoregulatory properties

Recent studies have sparked renewed interest in the therapeutic potential of psychedelics for treating depression and other mental health conditions. Simultaneously, the novel psychoactive substances (NPS) phenomenon, with a huge number of NPS emerging constantly, has changed remarkably the illicit drug market, being their scientific evaluation an urgent need. Thus, this study aims to elucidate the impact of amino-terminal modifications to the 5-MeO-DMT molecule on its interactions with serotonin receptors and transporters, as well as its psychoactive and thermoregulatory properties. Our findings demonstrated, using radioligand binding methodologies, that all examined 5-MeO-tryptamines exhibited selectivity for 5-HT1AR over 5-HT2AR. In fact, computational docking analyses predicted a better interaction in the 5-HT1AR binding pocket compared to 5-HT2AR. Our investigation also proved the interaction of these compounds with SERT, revealing that the molecular size of the amino group significantly influenced their affinity. Subsequent experiments involving serotonin uptake, electrophysiology, and superfusion release assays confirmed 5-MeO-pyr-T as the most potent partial 5-HT releaser tested. All tested tryptamines elicited, to some degree, the head twitch response (HTR) in mice, indicative of a potential hallucinogenic effect and mainly mediated by 5-HT2AR activation. However, 5-HT1AR was also shown to be implicated in the hallucinogenic effect, and its activation attenuated the HTR. In fact, tryptamines that produced a higher hypothermic response, mediated by 5-HT1AR, tended to exhibit a lower hallucinogenic effect, highlighting the opposite role of both 5-HT receptors. Moreover, although some 5-MeO-tryptamines elicited very low HTR, they still act as potent 5-HT2AR agonists. In summary, this research offers a comprehensive understanding of the psychopharmacological profile of various amino-substituted 5-MeO-tryptamines, keeping structural aspects in focus and accumulating valuable data in the frame of NPS. Moreover, the unique characteristics of some 5-MeO-tryptamines render them intriguing molecules as mixed-action drugs and provide insight within the search of non-hallucinogenic but 5-HT2AR ligands as therapeutical agents.

Content analysis of Reddit posts about coadministration of selective serotonin reuptake inhibitors and psilocybin mushrooms

RATIONALE

Treatments with the serotonergic psychedelic psilocybin are being investigated for multiple neuropsychiatric disorders. Because many patients with these disorders use selective serotonin reuptake inhibitors (SSRIs), understanding interactions between psilocybin and SSRIs is critical for evaluating the safety, efficacy, and scalability of psilocybin-based treatments. Current knowledge about these interactions is limited, as most clinical psilocybin research has prohibited concomittant SSRI use.

OBJECTIVES

We aimed to explore potential interactions between psilocybin and SSRIs by characterizing peoples' real-world experiences using psilocybin mushrooms and SSRIs together.

METHODS

We conducted a systematic search of Reddit for posts describing psilocybin mushroom and SSRI coadministration. We identified 443 eligible posts and applied qualitative content analysis to each.

RESULTS

8% of posts reported negative physical or psychological effects resulting from coadministration. These included 13 reports that may reflect serotonin toxicity, and 1 concerning for a psychotic/manic episode. 54% of posts described reduced intensity of the acute psilocybin experience, but 39% reported unchanged intensity with SSRI coadministration.

CONCLUSIONS

Psilocybin's interactions with SSRIs are likely complex and may depend on multiple factors. Prospective studies are needed to evaluate whether psilocybin treatments are reliably safe and effective in the setting of SSRI use.

The biosynthetic pathway of the hallucinogen mescaline and its heterologous reconstruction

Mescaline, among the earliest identified natural hallucinogens, holds great potential in psychotherapy treatment. Nonetheless, despite the existence of a postulated biosynthetic pathway for more than half a century, the specific enzymes involved in this process are yet to be identified. In this study, we investigated the cactus Lophophora williamsii (Peyote), the largest known natural producer of the phenethylamine mescaline. We employed a multi-faceted approach, combining de novo whole-genome and transcriptome sequencing with comprehensive chemical profiling, enzymatic assays, molecular modeling, and pathway engineering for pathway elucidation. We identified four groups of enzymes responsible for the six catalytic steps in the mescaline biosynthetic pathway, and an N-methyltransferase enzyme that N-methylates all phenethylamine intermediates, likely modulating mescaline levels in Peyote. Finally, we reconstructed the mescaline biosynthetic pathway in both Nicotiana benthamiana plants and yeast cells, providing novel insights into several challenges hindering complete heterologous mescaline production. Taken together, our study opens up avenues for exploration of sustainable production approaches and responsible utilization of mescaline, safeguarding this valuable natural resource for future generations.

Effects of congeners of amphetamine on the human heart

Central stimulatory and hallucinogenic drugs of abuse like amphetamine and most congeners of amphetamine can have cardiac harmful effects. These cardiac side effects can lead to morbidities and death. In this paper, we review current knowledge on the direct and indirect effects of these amphetamine congeners on the mammalian heart-more specifically, the isolated human heart muscle preparation. In detail, we address the question of whether and how these drugs affect cardiac contractility and their mechanisms of action. Based on this information, further research areas are defined, and further research efforts are proposed.

Psychedelic therapy in depression and substance use disorders

Psychoactive substances obtained from botanicals have been applied for a wide variety of purposes in the rituals of different cultures for thousands of years. Classical psychedelics from N,N'-dimethyltryptamine, psilocybin, mescaline and various lysergamides cause specific alterations in perception, emotion and cognition by acting through serotonin 5-HT2A receptor activation. Lysergic acid diethylamide, the first famous breakthrough in the field, was discovered by chance by Albert Hoffman in the Zurich Sandoz laboratory in 1943, and studies on its psychoactive effects began to take place in the literature. Studies in this area were blocked after the legislation controlling the use and research of psychedelic drugs came into force in 1967, but since the 1990s, it has started to be a matter of scientific curiosity again by various research groups. In particular, with the crucial reports of psychotherapy-assisted psilocybin applications for life-threatening cancer-related anxiety and depression, a new avenues have been opened in the treatment of psychiatric diseases such as treatment-resistant depression and substance addictions. An increasing number of studies show that psychedelics have a very promising potential in the treatment of neuropsychiatric diseases where the desired efficiency cannot be achieved with conventional treatment methods. In this context, we discuss psychedelic therapy, encompassing its historical development, therapeutic applications and potential treatment effects-especially in depression, trauma disorders and substance use disorders-within the framework of ethical considerations.

RE104: Synthesis and Activity of a Novel Serotonergic Psychedelic Prodrug of 4-Hydroxy-N,N-diisopropyltryptamine

Results from randomized clinical trials of psilocybin in depressive disorders highlight the therapeutic potential of serotonergic psychedelic compounds in mental health disorders. The synthetic 5-hydroxytryptamine 2A receptor agonist 4-hydroxy-N,N-diisopropyltryptamine (4-OH-DiPT) is structurally similar to psilocin but is reported to have a shorter duration (2-3 h) of psychedelic effects, suggesting the potential for psilocybin-like therapeutic activity with reduced clinical resource burden. Here, we describe the preclinical and translational characterization of RE104, a 4-OH-DiPT prodrug comprising a glutarate moiety designed to cleave rapidly in situ and thus provide reasonable bioavailability of the active drug. Plasma concentration of 4-HO-DiPT over time in PK experiments in rats was correlated with head-twitch intensity. The half-life of 4-OH-DiPT was 40 min after subcutaneous administration of RE104 in rats. In a forced swim test, a single dose of RE104 (1 mg/kg) significantly reduced mean immobility time at 1 week compared with vehicle (P < 0.001), confirming translational antidepressant potential. Taken together, these data with RE104 show that the glutarate ester can act as an efficient prodrug strategy for 4-HO-DiPT, a unique short-duration psychedelic with potential in depressive disorders.

Characterization of iso-LSD metabolism using human liver microsomes in comparison to LSD and its applicability as urinary biomarker for LSD consumption

Urinalysis of lysergic acid diethylamide (LSD) poses a challenge due to its rapid metabolism, resulting in little to no LSD detectable in urine. Instead, its primary metabolite, 2-oxo-3-hydroxy-LSD, is predominantly detected. In this study, we observed several urine profiles with iso-LSD detected together with 2-oxo-3-hydroxy-LSD. Iso-LSD is derived from illicit preparation of LSD as a major contaminant, and it was detected at higher abundance than LSD and 2-oxo-3-hydroxy-LSD in certain urine samples. Therefore, the metabolism of iso-LSD and its potential as a viable urinary biomarker for confirming LSD consumption is of interest. For metabolism studies, LSD and iso-LSD were incubated in human liver microsomes (HLMs) at 0 min, 60 min and 120 min to characterize their metabolites using LC-QTOF-MS. For urinary analysis, 500 µL of urine samples underwent enzymatic hydrolysis and clean-up using supported-liquid extraction (SLE) prior to analysis by LC-QTOF-MS. From HLM incubation study of LSD, the metabolites detected were dihydroxy-LSD, 2-oxo-LSD, N-desmethyl-LSD (nor-LSD) and 2-oxo-3-hydroxy-LSD with LSD levels decreasing significantly throughout all time points, consistent with the existing literatures. For HLM study of iso-LSD, metabolites eluting at retention times after the corresponding metabolites of LSD were detected, with iso-LSD levels showing only a slight decrease throughout all time points, due to a slower metabolism of iso-LSD compared to LSD. These findings corroborate with the urinalysis of 24 authentic urine samples, where iso-LSD with 2-oxo-3-hydroxy-LSD was detected in the absence of LSD. Based on our findings, iso-LSD is commonly detected in urine (18 out of 24 samples) sometimes with traces of possible 2-oxo-3-hydroxy-iso-LSD. The slower metabolism and high detection rate in urine make iso-LSD a viable urinary biomarker for confirming LSD consumption, especially in the absence of LSD and/or 2-oxo-3-hydroxy-LSD.

Dose-dependent LSD effects on cortical/thalamic and cerebellar activity: brain oxygen level-dependent fMRI study in awake rats

Lysergic acid diethylamide is a hallucinogen with complex neurobiological and behavioural effects. This is the first study to use MRI to follow functional changes in brain activity in response to different doses of lysergic acid diethylamide in fully awake, drug-naive rats. We hypothesized that lysergic acid diethylamide would show a dose-dependent increase in activity in the prefrontal cortex and thalamus while decreasing hippocampal activity. Female and male rats were given intraperitoneal injections of vehicle or lysergic acid diethylamide in doses of 10 or 100 µg/kg while fully awake during the imaging session. Changes in blood oxygen level-dependent signal were recorded over a 30-min window. Approximately 45-min post-injection data for resting-state functional connectivity were collected. All data were registered to rat 3D MRI atlas with 173 brain regions providing site-specific increases and decreases in global brain activity and changes in functional connectivity. Treatment with lysergic acid diethylamide resulted in a significant dose-dependent increase in negative blood oxygen level-dependent signal. The areas most affected were the primary olfactory system, prefrontal cortex, thalamus and hippocampus. This was observed in both the number of voxels affected in these brains regions and the changes in blood oxygen level-dependent signal over time. However, there was a significant increase in functional connectivity between the thalamus and somatosensory cortex and the cerebellar nuclei and the surrounding brainstem areas. Contrary to our hypothesis, there was an acute dose-dependent increase in negative blood oxygen level-dependent signal that can be interpreted as a decrease in brain activity, a finding that agrees with much of the behavioural data from preclinical studies. The enhanced connectivity between thalamus and sensorimotor cortices is consistent with the human literature looking at lysergic acid diethylamide treatments in healthy human volunteers. The unexpected finding that lysergic acid diethylamide enhances connectivity to the cerebellar nuclei raises an interesting question concerning the role of this brain region in the psychotomimetic effects of hallucinogens.

Disentangling the acute subjective effects of classic psychedelics from their enduring therapeutic properties

Recent research with classic psychedelics suggests significant therapeutic potential, particularly for neuropsychiatric disorders. A mediating influence behind symptom resolution is thought to be the personal insight - at times, bordering on the mystical - one acquires during the acute phase of a psychedelic session. Indeed, current clinical trials have found strong correlations between the acute subjective effects (ASE) under the influence of psychedelics and their enduring therapeutic properties. However, with potential barriers to widespread clinical implementation, including the healthcare resource-intensive nature of psychedelic sessions and the exclusion of certain at-risk patient groups, there is an active search to determine whether ASE elimination can be accompanied by the retention of persisting therapeutic benefits of these class of compounds. Recognizing the aberrant underlying neural circuitry that characterizes a range of neuropsychiatric disorders, and that classic psychedelics promote neuroplastic changes that may correct abnormal circuitry, investigators are rushing to design and discover compounds with psychoplastogenic, but not hallucinogenic (i.e., ASE), therapeutic potential. These efforts have paved the discovery of 'non-psychedelic/subjective psychedelics', or compounds that lack hallucinogenic activity but with therapeutic efficacy in preclinical models. This review aims to distill the current evidence - both clinical and preclinical - surrounding the question: can the ASE of classic psychedelics be dissociated from their sustained therapeutic properties? Several plausible clinical scenarios are then proposed to offer clarity on and potentially answer this question.

Serotonergic Psychedelics: A Comparative Review of Efficacy, Safety, Pharmacokinetics, and Binding Profile

Psychedelic compounds, including psilocybin, LSD (lysergic acid diethylamide), DMT (N,N -dimethyltryptamine), and 5-MeO-DMT (5-methoxy-N,N-dimethyltryptamine), all of which are serotonin 2A receptor agonists, are being investigated as potential treatments. This review aims to summarize the current clinical research on these 4 compounds and mescaline to guide future research. Their mechanism(s) of action, pharmacokinetics, pharmacodynamics, efficacy, and safety were reviewed. While evidence for therapeutic indications, with the exception of psilocybin for depression, is still relatively scarce, we noted no differences in psychedelic effects beyond effect duration. Therefore, it remains unclear whether different receptor profiles contribute to the therapeutic potential of these compounds. More research is needed to differentiate these compounds in order to inform which compounds might be best for different therapeutic uses.

Epigenetic drugs and psychedelics as emerging therapies for alcohol use disorder: insights from preclinical studies

Alcohol use disorder (AUD) is a public health issue that affects millions of people worldwide leading to physical, mental and socio-economic consequences. While current treatments for AUD have provided relief to individuals, their effectiveness on the long term is often limited, leaving a number of affected individuals without sustainable solutions. In this review, we aim to explore two emerging approaches for AUD: psychedelics and epigenetic drugs (i.e., epidrugs). By examining preclinical studies, different animal species and procedures, we delve into the potential benefits of each of these treatments in terms of addictive behaviors (alcohol drinking and seeking, motivation to drink alcohol and prevention of relapse). Because psychedelics and epidrugs may share common and complementary mechanisms of action, there is an exciting opportunity for exploring synergies between these approaches and their parallel effectiveness in treating AUD and the diverse associated psychiatric conditions.

Effective Connectivity of Thalamocortical Interactions Following d-Amphetamine, LSD, and MDMA Administration

BACKGROUND

While the exploration of serotonergic psychedelics as psychiatric medicines deepens, so does the pressure to better understand how these compounds act on the brain.

METHODS

We used a double-blind, placebo-controlled, crossover design and administered lysergic acid diethylamide (LSD), 3,4-methylenedioxymethamphetamine (MDMA), and d-amphetamine in 25 healthy participants. By using spectral dynamic causal modeling, we mapped substance-induced changes in effective connectivity between the thalamus and different cortex types (unimodal vs. transmodal) derived from a previous study with resting-state functional magnetic resonance imaging data. Due to the distinct pharmacological modes of action of the 3 substances, we were able to investigate specific effects mainly driven by different neurotransmitter systems on thalamocortical and corticothalamic interactions.

RESULTS

Compared with placebo, all 3 substances increased the effective connectivity from the thalamus to specific unimodal cortices, whereas the influence of these cortices on the thalamus was reduced. These results indicate increased bottom-up and decreased top-down information flow between the thalamus and some unimodal cortices. However, for the amphetamines, we found the opposite effects when examining the effective connectivity with transmodal cortices, including parts of the salience network. Intriguingly, LSD increased the effective connectivity from the thalamus to both unimodal and transmodal cortices, indicating a breach in the hierarchical organization of ongoing brain activity.

CONCLUSIONS

The results advance our knowledge about the action of psychedelics on the brain and refine current models aiming to explain the underlying neurobiological processes.

In vitro and in vivo metabolism of psilocybin's active metabolite psilocin

In vivo, psilocybin is rapidly dephosphorylated to psilocin which induces psychedelic effects by interacting with the 5-HT2A receptor. Psilocin primarily undergoes glucuronidation or conversion to 4-hydroxyindole-3-acetic acid (4-HIAA). Herein, we investigated psilocybin's metabolic pathways in vitro and in vivo, conducting a thorough analysis of the enzymes involved. Metabolism studies were performed using human liver microsomes (HLM), cytochrome P450 (CYP) enzymes, monoamine oxidase (MAO), and UDP-glucuronosyltransferase (UGT). In vivo, metabolism was examined using male C57BL/6J mice and human plasma samples. Approximately 29% of psilocin was metabolized by HLM, while recombinant CYP2D6 and CYP3A4 enzymes metabolized nearly 100% and 40% of psilocin, respectively. Notably, 4-HIAA and 4-hydroxytryptophol (4-HTP) were detected with HLM but not with recombinant CYPs. MAO-A transformed psilocin into minimal amounts of 4-HIAA and 4-HTP. 4-HTP was only present in vitro. Neither 4-HIAA nor 4-HTP showed relevant interactions at assessed 5-HT receptors. In contrast to in vivo data, UGT1A10 did not extensively metabolize psilocin in vitro. Furthermore, two putative metabolites were observed. N-methyl-4-hydroxytryptamine (norpsilocin) was identified in vitro (CYP2D6) and in mice, while an oxidized metabolite was detected in vitro (CYP2D6) and in humans. However, the CYP2D6 genotype did not influence psilocin plasma concentrations in the investigated study population. In conclusion, MAO-A, CYP2D6, and CYP3A4 are involved in psilocin's metabolism. The discovery of putative norpsilocin in mice and oxidized psilocin in humans further unravels psilocin's metabolism. Despite limitations in replicating phase II metabolism in vitro, these findings hold significance for studying drug-drug interactions and advancing research on psilocybin as a therapeutic agent.