Dose-response relationships of psilocybin-induced subjective experiences in humans

The Afterglow Inventory (AGI): Validation of a new instrument for measuring subacute effects of classic serotonergic psychedelics

BACKGROUND

Classic psychedelics such as psilocybin and lysergic acid diethylamide are anecdotally associated with the phenomenon of "psychedelic afterglow," a set of predominantly pleasant, temporary psychological effects reported after the acute effects have subsided. Since post-acute effects are crucial for the therapeutic use of psychedelics, an instrument to systematically assess subacute "afterglow" effects is needed.

AIMS

To create and validate a questionnaire to quantify the subacute "afterglow" effects of psychedelics.

METHODS

An international online survey was conducted in English and German. Participants who had consumed a psychedelic (N = 1323) or another non-psychedelic substance (control group, N = 157) within the past 4 weeks were included. An initial list of 97 items was progressively reduced to 24 items.

RESULTS

A 5-factor structure best fit the data and showed high internal consistency. The factors included (1) vitality, (2) transpersonal aspects, (3) inspiration/creativity, (4) interpersonal relationships, and (5) relationship to nature. The final 24-item version of the Afterglow Inventory (AGI) effectively differentiated between the psychedelic group and the control group. The overall AGI score positively correlated with the intensity (r = 0.165; p < 0.001) and positive valence (r = 0.251; p < 0.001) of the acute psychedelic effects.

CONCLUSIONS

The AGI is a novel scale for quantifying positive subacute ("afterglow") effects of psychedelics. The use of the AGI could lead to a better understanding of the interplay between acute, subacute, and long-term effects of psychedelics. Insights could also be gained into how different substances, dosages, and extra-pharmacological factors, such as psychotherapy, might influence outcomes.

Insights on psychedelics: A systematic review of therapeutic effects

BACKGROUND

Insight - a sudden change in understanding or perspective that feels true or reliable - is a common occurrence during psychedelic experiences, and often considered by clinicians and patients to be central to their therapeutic value. However, their occurrence and role has not been systematically assessed.

OBJECTIVES

We reviewed all peer-reviewed studies that published data on insight catalysed by a classic psychedelic at psychoactive levels to elucidate several aspects of psychedelic-catalysed insight, including its prevalence, relationship to dose, time-course, and relationship to therapeutic outcomes. Risk of bias was assessed regarding selection, reliability, causality, and transparency. PROSPERO registration: CRD42023405854 FINDINGS: The final database and key bibliography searches were completed on July 13, 2024. We screened 741 abstracts and included 98 studies (40 survey, 58 interventional). Insight was positively correlated with psychedelic dose, and was significantly higher following psychedelics in 43 of 46 (93 %) studies that presented a comparison to a placebo condition. Crucially, 25 of 29 studies (86 %) found that insight was associated with therapeutic improvement, and this relationship was often stronger than mystical-type experience, which has received more research attention.

INTERPRETATION

This review indicates that psychedelic-catalysed insight is associated with therapeutic improvement, suggesting its importance for clinical practice and for understanding the mechanisms of psychedelic therapy.

LIMITATIONS

Heterogeneous study designs and operationalisations of insight precluded a meta-analytic summary. Publication bias and selective reporting is possible, given insight was typically not a primary outcome of the included studies.

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.

The role of the psychedelic experience in psilocybin treatment for treatment-resistant depression

OBJECTIVE

To determine the relationships between psilocybin dose, psychedelic experiences, and therapeutic outcome in treatment-resistant depression.

METHODS

For treatment-resistant depression, 233 participants received a single dose of 25, 10, or 1 mg of COMP360 psilocybin (a proprietary, pharmaceutical-grade synthesized psilocybin formulation, developed by the sponsor, Compass Pathfinder Ltd.) with psychological support. The resulting psychedelic experience (Five-Dimensional Altered States of Consciousness questionnaire [5D-ASC] and Emotional Breakthrough Inventory [EBI]) were measured. These proximal variables and outcome 3 weeks post-administration (change in Montgomery-Åsberg Depression Rating Scale [MADRS]) were explored using correlation analysis.

RESULTS

The mean intensity of psychedelic effects was dose-related, but distributions of scores for different doses overlapped considerably. Depression response correlated with select aspects of the psychedelic experience overall and for individual doses. At the 25 mg dose, 5D-ASC dimensions Oceanic Boundlessness (Pearson correlation coefficient r = -0.508) and Visual Restructuralization (r = -0.516), and EBI (r = -0·637) were the variables with the strongest correlation to the Week 3 change from Baseline in MADRS score.

LIMITATIONS

The existence of correlation does not establish causation and exploratory findings require further replication, preferably in larger independent samples.

CONCLUSIONS

The intensity of psychedelic experience overlaps widely across doses and mitigates the risk of unblinding to dose. Correlations between psychedelic experience and outcome suggest specificity in psilocybin's mechanism of action. Quality and intensity of psychedelic experience may be a measure of pharmacodynamic effect and reveal an effective dose response phenomenon for single oral doses.

Reconsidering evidence for psychedelic-induced psychosis: an overview of reviews, a systematic review, and meta-analysis of human studies

BACKGROUND

Persons with schizophrenia are excluded from psychedelic-assisted therapy due to concerns about the risk of triggering or worsening psychosis. However, there is limited meta-analytic data on the risk of psychedelic-induced psychosis in individuals with pre-existing psychotic disorders.

METHODS

We conducted a systematic review, meta-analysis, and overview of reviews to assess the incidence of psychedelic-induced psychosis and symptom exacerbation in schizophrenia. Our pre-registered protocol (CRD42023399591) covered: LSD, psilocybin, mescaline, DMT, and MDMA, using data from Embase, PubMed, PsyARTICLES, PsyINFO, and trial registries up to November 2023. A random-effects model was used to calculate psychosis incidence, with standardized assessments of study quality.

RESULTS

From 131 publications, we analyzed 14 systematic reviews, 20 reviews, 35 randomized-controlled trials (RCTs), 10 case-control studies, 30 uncontrolled trials (UCTs), and 22 cohort studies, most of which were low quality. Meta-analysis of nine studies showed an incidence of psychedelic-induced psychosis at 0.002% in population studies, 0.2% in UCTs, and 0.6% in RCTs. In UCTs including individuals with schizophrenia, 3.8% developed long-lasting psychotic symptoms. Of those with psychedelic-induced psychosis, 13.1% later developed schizophrenia. Sensitivity analyses confirmed the results.

CONCLUSION

In summary, the reviewed evidence suggests that schizophrenia might not be a definite exclusion criterion for clinical trials exploring safety and efficacy of psychedelics for treatment-resistant depression and negative symptoms. However, given the low quality and limited number of studies, more high-quality research is needed, and a conservative approach is recommended until further data is available.

Exploring factors associated with the intensity of a mystical experience following naturalistic psychedelic use: A retrospective survey

INTRODUCTION

The intensity of the psychedelic experience has been hypothesized as the main predictor of response to a psychedelic treatment. This study aimed to investigate factors that may be associated with the intensity of mystical experiences during naturalistic psychedelic use.

METHODS

The data of this comprehensive sample were aggregated from four previous retrospective surveys, where mystical experience intensity was assessed using the mystical experience questionnaire (MEQ-30). Additional collected data included psychological flexibility levels, intentions regarding psychedelic use, substance used, subjective dosage levels, and socio-demographic information. ANOVA and linear regression were performed to identify predictors of MEQ-30 scores.

RESULTS

A total of 1657 participants were included in this study. The significant predictors of the total MEQ score were: the main motive for the psychedelic experience (with a greater impact of spiritual/religious, therapeutic, and self-exploration, compared to recreational), the type of substance used (with a higher impact for Ayahuasca and lysergic acid diethylamide than psilocybin), the subjective dosage (higher impact of very high, high, and moderate doses, compared to a very low dose), the number of psychedelic sessions, the time elapsed since the experience, and concomitant alcohol use.

CONCLUSION

This large sample study highlights significant associations between the intensity of mystical experiences during naturalistic psychedelic use and several key factors: the type of the psychedelic substance used, dosage, and set, particularly participants' intentions. Moreover, results show that concomitant alcohol use is associated with less intense psychedelic experiences, emphasizing the relevance of screening participants for substance use in research settings.

Acute effects of psilocybin on attention and executive functioning in healthy volunteers: a systematic review and multilevel meta-analysis

RATIONALE

Psilocybin shows promise for treating neuropsychiatric disorders. However, insight into its acute effects on cognition is lacking. Given the significant role of executive functions in daily life and treatment efficacy, it is crucial to evaluate how psilocybin influences these cognitive domains.

OBJECTIVES

This meta-analysis aims to quantify the acute effects of psilocybin on executive functions and attention, while examining how dosage, timing of administration, cognitive domain, and task characteristics moderate these effects.

METHODS

A systematic review and multilevel meta-analysis were conducted on empirical studies assessing psilocybin's acute effects on working memory, conflict monitoring, response inhibition, cognitive flexibility, and attention. Effect sizes for reaction time (RT) and accuracy (ACC) were calculated, exploring the effects of timing (on-peak defined as 90-180 min post-administration), dosage, cognitive function categories, and task sensitivity to executive functions as potential moderators.

RESULTS

Thirteen studies (42 effect sizes) were included. In the acute phase, psilocybin increased RTs (Hedges' g = 1.13, 95% CI [0.57, 1.7]) and did not affect ACC (Hedges' g = -0.45, 95% CI [-0.93, 0.034]). Effects on RT were dose dependent. Significant between-study heterogeneity was found for both RT and ACC. Task sensitivity to executive functions moderated RT effects. Publication bias was evident, but the overall effect remained significant after adjustment for this.

CONCLUSIONS

Our meta-analysis shows that psilocybin impairs executive functions and results in a slowing down of RT. We discuss potential neurochemical mechanisms underlying the observed effects as well as implications for the safe use of psilocybin in clinical and experimental contexts.

Harnessing Pharmacogenomics in Clinical Research on Psychedelic-Assisted Therapy

Psychedelics have recently re-emerged as potential treatments for various psychiatric conditions that impose major public health costs and for which current treatment options have limited efficacy. At the same time, personalized medicine is increasingly being implemented in psychiatry to provide individualized drug dosing recommendations based on genetics. This review brings together these topics to explore the utility of pharmacogenomics (a key component of personalized medicine) in psychedelic-assisted therapies. We summarized the literature and explored the potential implications of genetic variability on the pharmacodynamics and pharmacokinetics of psychedelic drugs including lysergic acid diethylamide (LSD), psilocybin, N,N-dimethyltryptamine (DMT), 5-methoxy-N,N-dimethyltryptamine (5-MeO-DMT), ibogaine and 3,4-methylenedioxymethamphetamine (MDMA). Although existing evidence is limited, particularly concerning pharmacodynamics, studies investigating pharmacokinetics indicate that genetic variants in drug-metabolizing enzymes, such as cytochrome P450, impact the intensity of acute psychedelic effects for LSD and ibogaine, and that a dose reduction for CYP2D6 poor metabolizers may be appropriate. Furthermore, based on the preclinical evidence, it can be hypothesized that CYP2D6 metabolizer status might contribute to altered acute psychedelic experiences with 5-MeO-DMT and psilocybin when combined with monoamine oxidase inhibitors. In conclusion, considering early evidence that genetic factors can influence the effects of certain psychedelics, we suggest that pharmacogenomic testing should be further investigated in clinical research. This is necessary to evaluate its utility in improving the safety and therapeutic profile of psychedelic therapies and a potential future role in personalizing psychedelic-assisted therapies, should these treatments become available.

Compass Psychological Support Model for COMP360 Psilocybin Treatment of Serious Mental Health Conditions

The psychedelic experience can be challenging. There is a need for a structured framework for providing psychological support to individuals with mental health conditions receiving investigational psilocybin treatment. The primary benefit of such a framework is to support a safe and meaningful psilocybin experience. It also enables future research on the facets of psychological support and/or psychotherapy that most optimally complement psilocybin treatment. The authors describe the Compass Psychological Support Model (CPSM), currently used to support participants with treatment-resistant depression in Compass-sponsored clinical trials of investigational COMP360 psilocybin treatment. The authors also outline the therapist training, mentoring, and fidelity assessment programs they have developed to ensure the quality and consistency of the CPSM delivery.

Phenomenology of Psychedelic Experiences and Psychedelic-Associated Distressing Effects: Quantifying Subjective Experiences

The range of phenomena that can be induced by psychedelic substances is broad and variable, including effects on perception, cognition, and emotion. The umbrella term "psychedelic phenomenology" is used to refer to a combination of altered experiential features, such as hallucinations or ego dissolution, which together constitute a psychedelic experience. However, there is no consensus on the set of alterations of consciousness that qualifies an altered state to be a "psychedelic state." In this chapter we summarize the most commonly discussed changes in subjective experiences which could be seen as "core features" of psychedelic experiences. While acknowledging the rich history of pioneering phenomenological work of the last century, this chapter focuses on more recent developments in the quantitative work on the assessment of these phenomena. We also address the under-researched phenomenology of distressing effects, often referred to as "challenging experiences" or "bad trips," and point to their importance in understanding the therapeutic potential and risks associated with psychedelic phenomenology. Historically, one can find many links between psychedelic phenomenology and the phenomenology of psychopathology. We stress the importance to refine the assessment and description also of distressing effects, to identify factors that promote acute experiences which are beneficial and limit those which can have potentially harmful long-term effects.

Enhanced visual contrast suppression during peak psilocybin effects: Psychophysical results from a pilot randomized controlled trial

In visual perception, an effect known as surround suppression occurs wherein the apparent contrast of a center stimulus is reduced when it is presented within a higher-contrast surrounding stimulus. Many key aspects of visual perception involve surround suppression, yet the neuromodulatory processes involved remain unclear. Psilocybin is a serotonergic psychedelic compound known for its robust effects on visual perception, particularly texture, color, object, and motion perception. We asked whether surround suppression is altered under peak effects of psilocybin. Using a contrast-matching task with different center-surround stimulus configurations, we measured surround suppression after 25 mg of psilocybin compared with placebo (100 mg niacin). Data on harms were collected, and no serious adverse events were reported. After taking psilocybin, participants (n = 6) reported stronger surround suppression of perceived contrast compared to placebo. Furthermore, we found that the intensity of subjective psychedelic visuals induced by psilocybin correlated positively with the magnitude of surround suppression. We note the potential relevance of our findings for the field of psychiatry, given that studies have demonstrated weakened visual surround suppression in both major depressive disorder and schizophrenia. Our findings are thus relevant to understanding the visual effects of psilocybin, and the potential mechanisms of visual disruption in mental health disorders.

Mystical and Affective Aspects of Psychedelic Use in a Naturalistic Setting: A Linguistic Analysis of Online Experience Reports

Analyzing online retrospective experience reports of psychedelic use can provide valuable insight into their acute subjective effects. Such reports are unexplored in relation to mystical states, which are thought to be a therapeutic mechanism within psychedelic-assisted psychotherapy. We created a set of words that, when encountered in an experience report, indicate the occurrence of mystical elements within the experience. We used the Shroomery.org website to retrieve 7317 publicly available retrospective psychedelic experience reports of psychedelic use, primarily of psilocybin, and have a designated experience intensity level self-assessed by the text authors during submission of the report. We counted the mystical language words using Linguistic Inquiry and Word Count (LIWC) software and additionally performed sentiment analysis of all reports. We found that the occurrence of mystical language grew with increased self-reported experience intensity. We also found that negative sentiment increased, and positive sentiment decreased as self-reported psychedelic experience intensity increased. These two findings raise the question of whether mystical experiences can co-exist with challenging elements within the psychedelic experience, a consideration for future qualitative studies. We present a new mystical language dictionary measure for further use and expansion, with some suggestions on how it can be used in future studies.

Low-dose psilocybin in short-lasting unilateral neuralgiform headache attacks: results from an open-label phase Ib ascending dose study

BACKGROUND

Short-lasting unilateral neuralgiform headache attacks (SUNHA) are trigeminal autonomic cephalalgias that feature intense and recurrent paroxysms of pain and autonomic symptoms. Many patients are left with debilitating symptoms despite best-available treatment. Psychedelics, such as the serotonin 2A partial agonist psilocybin, have shown promise in related disorders such as migraine and cluster headache. In this open-label phase Ib ascending dose study, we aimed to assess the effects of low-dose oral psilocybin with psychological support in six to 12 patients with chronic SUNHA. Study objectives were to determine effects on cognition, as well as safety, tolerability, and effects on headache severity and frequency.

METHODS

Oral psilocybin in ascending doses of 5, 7.5, and 10 mg (one dose per session; three dosing sessions in total) were administered. Cognition was assessed via the Cambridge Neuropsychological Tests Automated Battery. Headache attacks were assessed via headache diaries and the six-item Headache Impact Test (HIT-6). Subjective dose intensity was assessed via the five-Dimensional Altered States of Consciousness Questionnaire (5D-ASC). The study was terminated early due to recruitment difficulties; four patients were enrolled, three of whom were study completers. Post hoc, we undertook a thematic analysis of the applicable free-text clinical trial notes from the dosing and subsequent visits (n = 22). An inductive method was employed to establish emergent themes.

RESULTS

No significant adverse events were recorded. We were unable to collect data as planned on cognitive function during the acute experience due to high ratings of subjective dose intensity (mean 5D-ASC scores 37.8-45.7). The impact of the headaches remained severe throughout the duration of the trial (HIT-6 mean scores 64.3-65.7). There were limited effects on headache duration and severity based on the diaries; however, mean daily attack frequency decreased by >50% in two participants at final follow-up (22.9 to 11.0 and 56.4 to 28.0, respectively). Completing participants and their clinicians recorded "much" (two participants) or "minimal" improvements (one participant) at final follow-up via the Clinical Global Impression rating scale. Thematic analysis indicated that psychological insights were key features of participants' experience; these insights included re-configured relationships to their headache pain.

CONCLUSION

The study met with recruitment difficulties and cognition could not be assessed during the acute experience due to subjective dose intensity, likely mediated in part by expectancy effects. The clinical results provide no conclusive evidence for the use of psilocybin in SUNHA. We suggest that accounting for psychological factors in chronic SUNHA may be an important facet of treatment.

Altered states of consciousness in Danish healthy volunteers and recreational users of psilocybin and the possible impact of setting and intention: Danish validation of the five-dimensional altered states of consciousness questionnaire

BACKGROUND

Psychedelic substances reliably induce marked altered states of consciousness (ASC), which may be important for lasting effects and clinical outcomes of psychedelic intervention. Several instruments are available to measure the acute psychedelic experience, of which the Five Dimensional Altered States of Consciousness Questionnaire (5D-ASC) is commonly used. The questionnaire can be scored and analyzed as having five dimensions or 11 subscales, but the two have not been evaluated with comparable factor analysis methods.

METHODS

The Danish translation of the 5D-ASC was completed by one sample of healthy volunteers receiving psilocybin in a laboratory setting (N = 47) and one sample of recreative users5D-ASC of psychedelics (N = 550), who reported retrospectively through an online survey based on their most recent experience with psilocybin. We calculated internal consistency measures of Cronbach's alpha and McDonald's omega, conducted a confirmatory factor analysis of the previously suggested factor structures, and tested for possible associations between the 5D-ASC total scores and dose, setting, and intention. For the 11 subscales, we reported omega-sem (composite reliability) using the parameters of the fitted confirmatory factor analyses model.

RESULTS

Confirmatory factor analysis showed that the 11 subscales had a good fit to data and showed a better fit compared to the originally proposed five-dimensional solution and good internal consistencies. We further found that the 5D-ASC total scores correlated positively with the dose in the recreative sample. We found no correlations between 5D-ASC total scores and intention or setting.

DISCUSSION

We find the Danish 5D-ASC to be a valid tool for measuring ASC among Danish-speaking individuals.

Pharmacological and non-pharmacological predictors of the LSD experience in healthy participants

The pharmacodynamic effects of lysergic acid diethylamide (LSD) are diverse and different in different individuals. Effects of other psychoactive substances have been shown to be critically influenced by non-pharmacological factors such as personality traits and mood states. The aim of this study was to determine pharmacological and psychological predictors of the LSD effects in healthy human subjects. This analysis is based on nine double-blind, placebo-controlled, cross-over studies with a total of 213 healthy subjects receiving between 25-200 µg LSD. The influence of sex, age, dose, body weight, pharmacogenetic, drug experience, personality, setting, and mood before drug intake on the peak autonomic and total subjective responses to LSD was investigated using multiple linear mixed effects models and Least Absolute Shrinkage and Selection Operator regression. Results were adjusted for LSD dose and corrected for multiple testing. LSD dose emerged as the most influential predictor, exhibiting a positive correlation with most response variables. Pre-drug mental states such as "Well-Being", "Emotional Excitability", and "Anxiety" were also important predictor for a range of subjective effects but also heart rate and body temperature. The trait "Openness to Experiences" was positively correlated with elevated ratings in "Oceanic Boundlessness" and mystical-type effects. Previous experiences with hallucinogens have been negatively associated with the overall altered state of consciousness and particularly with "Anxious Ego Dissolution". Acute anxiety negatively correlated with the genetically determined functionality of the Cytochrome 2D6 enzyme. In summary, besides the amount of drug consumed, non-pharmacological factors such as personal traits and current mood also significantly predicted the subjective drug experience. Sex and body weight were not significant factors in influencing the drug experience.

A Cross-Sectional Survey Investigating Māori and Non-Māori Cancer Patients' Views on Psychedelic-Assisted Therapy in Aotearoa New Zealand

People with cancer experience higher rates of psychological dysfunction than the general population, with extreme inequity among indigenous people. Psychedelic-assisted therapy (PAT) is a reemerging area with promising evidence as a treatment for mental health difficulties. The current study aimed to investigate the perceptions of PAT in indigenous (Māori) and non-indigenous cancer patients in Aotearoa, New Zealand. Eighty-five cancer patients (Māori n = 32, non-Māori n = 53) completed a brief anonymous survey assessing demographics, psychological factors, and awareness and perceptions of PAT. Participants were recruited online (via social media and cancer support e-mail lists) and in person at Auckland City Hospital. Maori had significantly poorer psychological well-being than non-Māori. All participants had low awareness of this novel treatment and held largely neutral attitudes. Regression analyses revealed that predictors of more favorable attitudes toward PAT included greater awareness of psychedelics, advanced cancer stage, younger age, poorer holistic well-being, greater demoralization, and prioritizing treatment effectiveness over possible risks and uncertainty. The current study provides a foundational step in exploring perceptions toward PAT in indigenous and non-indigenous groups. These results have the potential to shape future research trials investigating PAT and further highlight the importance of indigenous involvement in the psychedelic research space.

Breathwork-induced psychedelic experiences modulate neural dynamics

Breathwork is an understudied school of practices involving intentional respiratory modulation to induce an altered state of consciousness (ASC). We simultaneously investigate the phenomenological and neural dynamics of breathwork by combining Temporal Experience Tracing, a quantitative methodology that preserves the temporal dynamics of subjective experience, with low-density portable EEG devices. Fourteen novice participants completed a course of up to 28 breathwork sessions-of 20, 40, or 60 min-in 28 days, yielding a neurophenomenological dataset of 301 breathwork sessions. Using hypothesis-driven and data-driven approaches, we found that "psychedelic-like" subjective experiences were associated with increased neural Lempel-Ziv complexity during breathwork. Exploratory analyses showed that the aperiodic exponent of the power spectral density-but not oscillatory alpha power-yielded similar neurophenomenological associations. Non-linear neural features, like complexity and the aperiodic exponent, neurally map both a multidimensional data-driven composite of positive experiences, and hypothesis-driven aspects of psychedelic-like experience states such as high bliss.

Altered states of consciousness caused by a mindfulness-based programme up to a year later: Results from a randomised controlled trial

BACKGROUND

Mindfulness-based programmes (MBPs) have shown beneficial effects on mental health. There is emerging evidence that MBPs may also be associated with marked deviations in the subjective experience of waking consciousness. We aimed to explore whether MBPs can have a causal role in different types of such states.

METHODS

We conducted a pragmatic randomised controlled trial (ACTRN12615001160527). University of Cambridge students without severe mental illness were randomised to an 8-week MBP plus mental health support as usual (SAU), or to SAU alone. We adapted the Altered States of Consciousness Rating Scale (OAV, 0-100-point range) to assess spontaneous experiences in daily life, and included it as a post-hoc secondary outcome at the end of the one-year follow-up questionnaire. Two-part model analyses compared trial arms, and estimated dose-response effects of formal (meditation) and informal (daily activities) mindfulness practice during the year. Sensitivity analyses correcting for multiple comparisons were conducted.

RESULTS

We randomised 670 participants; 205 (33%) completed the OAV. In comparison with SAU, MBP participants experienced unity more frequently and intensively (two-part marginal effect (ME) = 6.26 OAV scale points, 95% confidence interval (CI) = 2.24, 10.27, p = 0.006, Cohen's d = 0.33) and disembodiment more frequently (ME = 4.84, 95% CI = 0.86, 8.83, p = 0.019, Cohen's d = 0.26). Formal practice predicted spiritual, blissful and unity experiences, insightfulness, disembodiment, and changed meanings. Informal practice predicted unity and blissful experiences. Trial arm comparisons and informal practice effects lost significance after corrections for multiple comparisons, but formal practice dose-response effects remained significant.

CONCLUSIONS

Results provide a novel suggestion of causal links between mindfulness practice and specific altered states of consciousness. To optimise their impact, practitioners and teachers need to anticipate and handle them appropriately. Future studies need to confirm findings and assess mechanisms and clinical implications.

Health Benefits and Positive Acute Effects of Psilocybin Consumption: A Quantitative Textual Analysis of User Self-Reported Data

There has been growth in the use of psychedelics by the global population in recent years. In addition to recreational and ritualistic use, recent research into psychedelics has brought advances for treating mental disorders. Understanding the specific circumstances in which psilocybin leads to positive outcomes may have important implications for the future of its clinical use and for harm reduction initiatives. This study aimed to investigate the positive effects from the consumption of psilocybin through public online self-reports. We sought to investigate health benefits promoted by the consumption of the substance, positive acute effects, and contextual details of these experiences. We analyzed 846 reports with the assistance of the IRaMuTeQ textual analysis software, adopting the procedures of Descending Hierarchical Classification, Correspondence Factor Analysis, and Specificities Analysis. The texts were grouped in 5 clusters, describing the content of mental experiences, cognitive processes, somatic experiences, perceptual alterations, and context of administration. The findings of this study reinforce central axes of the psychedelic experience, such as the presence of somatic and visual alterations, connectedness and feeling one with the world and effects of setting, as well as the beneficial character of mystical experiences this substance promotes, and the importance of the ego-dissolution phenomenon.

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.

Psychedelics and disorders of consciousness: the current landscape and the path forward

Modern medicine has been shaken by the surge of psychedelic science that proposes a new approach to mitigate mental disorders, such as depression and post-traumatic stress disorder. Clinical trials to investigate whether psychedelic substances can treat psychiatric conditions are now underway, yet less discussion gravitates around their use in neurological disorders due to brain injury. One suggested implementation of brain-complexity enhancing psychedelics is to treat people with post-comatose disorders of consciousness (DoC). In this article, we discuss the rationale of this endeavour, examining possible outcomes of such experiments by postulating the existence of an optimal level of complexity. We consider the possible counterintuitive effects of both psychedelics and DoC on the functional connectivity of the default mode network and its possible impact on selfhood. We also elaborate on the role of computational modelling in providing complementary information to experimental studies, both contributing to our understanding of the treatment mechanisms and providing a path towards personalized medicine. Finally, we update the discourse surrounding the ethical considerations, encompassing clinical and scientific values.

The Psychedelic Future of Post-Traumatic Stress Disorder Treatment

Post-traumatic stress disorder (PTSD) is a mental health condition that can occur following exposure to a traumatic experience. An estimated 12 million U.S. adults are presently affected by this disorder. Current treatments include psychological therapies (e.g., exposure-based interventions) and pharmacological treatments (e.g., selective serotonin reuptake inhibitors (SSRIs)). However, a significant proportion of patients receiving standard-of-care therapies for PTSD remain symptomatic, and new approaches for this and other trauma-related mental health conditions are greatly needed. Psychedelic compounds that alter cognition, perception, and mood are currently being examined for their efficacy in treating PTSD despite their current status as Drug Enforcement Administration (DEA)- scheduled substances. Initial clinical trials have demonstrated the potential value of psychedelicassisted therapy to treat PTSD and other psychiatric disorders. In this comprehensive review, we summarize the state of the science of PTSD clinical care, including current treatments and their shortcomings. We review clinical studies of psychedelic interventions to treat PTSD, trauma-related disorders, and common comorbidities. The classic psychedelics psilocybin, lysergic acid diethylamide (LSD), and N,N-dimethyltryptamine (DMT) and DMT-containing ayahuasca, as well as the entactogen 3,4-methylenedioxymethamphetamine (MDMA) and the dissociative anesthetic ketamine, are reviewed. For each drug, we present the history of use, psychological and somatic effects, pharmacology, and safety profile. The rationale and proposed mechanisms for use in treating PTSD and traumarelated disorders are discussed. This review concludes with an in-depth consideration of future directions for the psychiatric applications of psychedelics to maximize therapeutic benefit and minimize risk in individuals and communities impacted by trauma-related conditions.

Psilocybin-assisted therapy for depression: A systematic review and dose-response meta-analysis of human studies

Psilocybin is increasingly studied for its antidepressant effect, but its optimal dosage for depression remains unclear. We conducted a systematic review and a dose-response meta-analysis to find the optimal dosage of psilocybin to reduce depression scores. Following our protocol (CRD 42022220190) multiple electronic databases were searched from their inception until February 2023, to identify double-blind randomized placebo-controlled (RCTs) fixed-dose trials evaluating the use of psilocybin for adult patients with primary or secondary depression. A one-stage dose-response meta-analysis with restricted cubic splines was used. Cochrane risk of bias was used to assess risk of bias. Our analysis included seven studies with a total of 489 participants. Among these, four studies focused on primary depression (N = 366), including one study with patients suffering from treatment-resistant depression. The remaining three studies examined secondary depression (N = 123). The determined 95% effective doses per day (ED95) were 8.92, 24.68, and 36.08 mg/70 kg for patients with secondary depression, primary depression, and both subgroups, respectively. We observed significant dose-response associations for all curves, each plateauing at different levels, except for the bell-shaped curve observed in the case of secondary depression. Additionally, we found significant dose-response associations for various side effects, including physical discomfort, blood pressure increase, nausea/vomiting, headache/migraine, and the risk of prolonged psychosis. In conclusion, we discovered specific ED95 values for different populations, indicating higher ED95 values for treatment-resistant depression, primary depression, and secondary depression groups. Further RCTs are necessary for each population to determine the optimal dosage, allowing for maximum efficacy while minimizing side effects.

Dose-response relationships of LSD-induced subjective experiences in humans

Lysergic acid diethylamide (LSD) is a potent classic serotonergic psychedelic, which facilitates a variety of altered states of consciousness. Here we present the first meta-analysis establishing dose-response relationship estimates of the altered states of consciousness induced by LSD. Data extracted from articles identified by a systematic literature review following PRISMA guidelines were obtained from the Altered States Database. The psychometric data comprised ratings of subjective effects from standardized and validated questionnaires: the Altered States of Consciousness Rating Scale (5D-ASC, 11-ASC) and the Mystical Experience Questionnaire (MEQ30). We performed meta-regression analyses using restricted cubic splines for data from studies with LSD doses of up to 200 μg base. Most scales revealed a sigmoid-like increase of effects, with a plateauing at around 100 μg. The most strongly modulated factors referred to changes in perception and illusory imagination, followed by positively experienced ego-dissolution, while only small effects were found for Anxiety and Dread of Ego Dissolution. The considerable variability observed in most factors and scales points to the role of non-pharmacological factors in shaping subjective experiences. The established dose-response relationships may be used as general references for future experimental and clinical research on LSD to compare observed with expected subjective effects and to elucidate phenomenological differences between psychedelics.

Ecstatic or Mystical Experience through Epilepsy

Ecstatic epilepsy is a rare form of focal epilepsy, so named because the seizures' first symptoms consist of an ecstatic/mystical experience, including feelings of increased self-awareness, mental clarity, and "unity with everything that exists," accompanied by a sense of bliss and physical well-being. In this perspective article, we first describe the phenomenology of ecstatic seizures, address their historical context, and describe the primary brain structure involved in the genesis of these peculiar epileptic seizures, the anterior insula. In the second part of the article, we move onto the possible neurocognitive underpinnings of ecstatic seizures. We first remind the reader of the insula's role in interoceptive processing and consciously experienced feelings, contextualized by the theory of predictive coding. This leads us to hypothesize that temporary disruptions to activity in the anterior insula could interrupt the generation of interoceptive prediction errors, and cause one to experience the absence of uncertainty, and thereby, a sense of bliss. The absence of interoceptive prediction errors would in fact mimic perfect prediction of the body's physiological state. This sudden clarity of bodily perception could explain the ecstatic quality of the experience, as the interoceptive system forms the basis for unified conscious experience. Our alternative hypothesis is that the anterior insula plays an overarching role in the processing of surprise and that the dysfunction caused by the epileptic discharge could interrupt any surprise exceeding expectations, resulting in a sense of complete control and oneness with the environment.

Psilocybin for treatment resistant depression in patients taking a concomitant SSRI medication

Psilocybin is being investigated as a treatment in adults with treatment-resistant depression (TRD). Withdrawal from serotonergic antidepressant drugs is a common prerequisite for taking part in trials of psilocybin due to the possibility of ongoing antidepressant drugs altering the psychedelic effect. This phase II, exploratory, international, fixed-dose, open-label study explored the safety, tolerability, and efficacy of a synthetic form of psilocybin (investigational drug COMP360) adjunct to a selective serotonin reuptake inhibitor in participants with TRD. Participants received a single 25 mg dose of psilocybin alongside psychological support and were followed-up for 3 weeks. The primary efficacy end point was change in the Montgomery-Åsberg Depression Rating Scale (MADRS) total score from Baseline at Week 3. Secondary end points were safety, including treatment-emergent adverse events (TEAEs), the proportion of responders and remitters at Week 3, and the change from Baseline to Week 3 in Clinical Global Impression-Severity (CGI-S) score. Nineteen participants were dosed and the mean Baseline MADRS total score was 31.7 (SD = 5.77). Twelve (63.2%) participants had a TEAE, most of which were mild and resolved on the day of onset. There were no serious TEAEs or indication of increased suicidal ideation or behavior. At Week 3, mean change from Baseline in MADRS total score was -14.9 (95% CI, -20.7 to -9.2), and -1.3 (SD = 1.29) in the CGI-S. Both response and remission were evident in 8 (42.1%) participants. Larger, comparator-controlled trials are necessary to understand if this paradigm can optimize treatment-outcome where antidepressant drug withdrawal would be problematic.

Unblinding and demand characteristics in the treatment of depression

Blinding of treatment allocation in clinical trials in psychiatry is regarded as an ideal. The potential impact of unblinding chimes with a general concern for psychological research: so-called demand characteristics can undermine confidence in findings from experimental and clinical studies. Scepticism can result in nihilism. The reliance on subjective report of symptoms in clinical trials of drug efficacy in depression provides an important example. It is regularly implied that if subjective effects, including specific adverse reactions, unblind participants to an active treatment then evidence for its efficacy is suspect. In fact, the strong association between dose and subjective effects does not translate into a strong relationship with efficacy in randomised controlled trials (RCTs) of conventional antidepressant drugs; this observation falsifies the proposition that unblinding is the principal mechanism driving RCT outcomes in studies of depression. Instead, changes in brain function, that occur soon after treatment starts, do predict treatment outcomes and align with our understanding of neurotransmitter effects from neuroscience. Psychedelic experience for the treatment of depression must be unblinding, but the effect results directly from serotonergic receptor activation and changes in brain connectivity. Where such effects are part of a novel mechanism of action, a strong dose response relationship would be expected, irrespective of unblinding. We highlight the importance of exploring blinding as a mechanism, confirming dose-related outcomes, and dissociating unblinding effects from efficacy. Unblinding does not necessarily invalidate the subjective experience of sustained recovery from depression.

Optimizing outcomes in psilocybin therapy: Considerations in participant evaluation and preparation

Recent studies have demonstrated the promise of psilocybin therapies in creating positive changes for those with poor mental health across multiple diagnostic categories, including major depressive disorder (MDD), end-of-life anxiety, and obsessive-compulsive disorder (OCD). While there may be a large population that is eligible to participate in psilocybin therapy based on psychiatric diagnosis and medical clearance, little attention has been given to intrapersonal and interpersonal factors that might influence patient's readiness (i.e., eligibility and capacity) for psychedelic interventions. This paper proposes that readiness assessment includes both intrapersonal and interpersonal factors in order to improve safety, patient care, and treatment outcomes. While at the present time a reliable and valid instrument has not been developed, we propose that three specific areas of focus - patient presentation, therapeutic alliance, and patient safety - may be used to establish a patient's readiness for psilocybin therapy, thus increasing therapy optimization and personalization.

Recent Advances in the Psychopharmacology of Major Depressive Disorder

This review highlights some of the recent advances in the psychopharmacology of Major Depressive Disorder (MDD). We synthesise evidence on emerging pharmacological therapies targeting the serotonergic system, before exploring several novel treatment targets: the glutamatergic system, the GABAergic system, and inflammation. When describing new treatment avenues, we examine the evidence base and how far these new treatments are from routine practice.

The Altered States Database: Psychometric data from a systematic literature review

In this paper, we present the development of the Altered States Database (ASDB), an open-science project based on a systematic literature review. The ASDB contains psychometric questionnaire data on subjective experiences of altered states of consciousness (ASC) induced by pharmacological and non-pharmacological methods. The systematic review follows the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. Scientific journal articles were identified through PubMed and Web of Science. We included studies that examined ASC using the following validated questionnaires: Altered States of Consciousness Rating Scale (APZ, 5D-ASC, 11-ASC), Phenomenology of Consciousness Inventory (PCI), Hallucinogen Rating Scale (HRS), or Mystical Experience Questionnaire (MEQ30). The systematic review resulted in the inclusion of a total of 165 journal articles, whereof questionnaire data was extracted and is now available on the Open Science Framework (OSF) website (https://osf.io/8mbru) and on the ASDB website (http://alteredstatesdb.org), where questionnaire data can be easily retrieved and visualized. This data allows the calculation of comparable psychometric values of ASC experiences and of dose-response relationships of substances inducing ASC.

Measurement(s)	Psychometric questionnaire data
Technology Type(s)	Systematic literature review (PRISMA)
Sample Characteristic - Organism	Human

Molecular Pathways of the Therapeutic Effects of Ayahuasca, a Botanical Psychedelic and Potential Rapid-Acting Antidepressant

Ayahuasca is a psychoactive brew traditionally used in indigenous and religious rituals and ceremonies in South America for its therapeutic, psychedelic, and entheogenic effects. It is usually prepared by lengthy boiling of the leaves of the bush Psychotria viridis and the mashed stalks of the vine Banisteriopsis caapi in water. The former contains the classical psychedelic N,N-dimethyltryptamine (DMT), which is thought to be the main psychoactive alkaloid present in the brew. The latter serves as a source for β-carbolines, known for their monoamine oxidase-inhibiting (MAOI) properties. Recent preliminary research has provided encouraging results investigating ayahuasca's therapeutic potential, especially regarding its antidepressant effects. On a molecular level, pre-clinical and clinical evidence points to a complex pharmacological profile conveyed by the brew, including modulation of serotoninergic, glutamatergic, dopaminergic, and endocannabinoid systems. Its substances also interact with the vesicular monoamine transporter (VMAT), trace amine-associated receptor 1 (TAAR1), and sigma-1 receptors. Furthermore, ayahuasca's components also seem to modulate levels of inflammatory and neurotrophic factors beneficially. On a biological level, this translates into neuroprotective and neuroplastic effects. Here we review the current knowledge regarding these molecular interactions and how they relate to the possible antidepressant effects ayahuasca seems to produce.

Esketamine and Psilocybin—The Comparison of Two Mind-Altering Agents in Depression Treatment: Systematic Review

This publication discusses two compounds belonging to the psychoactive substances group which are studied in the context of depression treatment—psilocybin and esketamine. The former is a naturally occurring psychedelic. The latter was invented in the laboratory exactly 60 years ago. Although the substances were controversial in the past, recent studies indicate the potential of those substances as novel antidepressant agents. The PubMed/MEDLINE database was used to identify articles for systematic review, using the following search terms: (depression) AND (psilocybin) OR (ketamine). From 617 items, only 12 articles were obtained in the final analyses. Three articles were devoted to psilocybin in depression treatment and nine to esketamine. In most studies, esketamine showed a significant reduction in both depressive symptoms and suicidal ideation shortly after intake and after a month of treatment compared to baseline and to standard-of-care antidepressant agents. Psilocybin’s antidepressive effects occurred one day after intake and after 6–7 weeks of treatment and were maintained for up to 6 or 8 months of follow-up. One study indicated that psilocybin’s effects are comparable with and may be superior to escitalopram treatment. Both esketamine and psilocybin demonstrated rapid and long-term effects in reducing depression symptoms and, after overcoming some limitations, may be considered as novel antidepressant agents in future.

Unraveling the Mysteries of Mental Illness With Psilocybin

Current medications have not been effective in reducing the prevalence of mental illness worldwide. The prevalence of illnesses such as treatment-resistant depression has increased despite the widespread use of a broad set of psychopharmaceuticals. Transcranial magnetic stimulation and ketamine therapy are making great strides in improving treatment-resistant depression outcomes but they have limitations. New psychotherapeutics are required that specifically target the underlying cellular pathologies leading to neuronal atrophy. This neuronal atrophy model is supplanting the long-held neurotransmitter deficit hypothesis to explain mental illness. Interest in psychedelics as therapeutic molecules to treat mental illness is experiencing a 21st-century reawakening that is on the cusp of a transformation. Psilocybin is a pro-drug, found in various naturally occurring mushrooms, that is dephosphorylated to produce psilocin, a classic tryptamine psychedelic functional as a 5-hydroxytryptamine 2A receptor agonist. We have focused this review to include studies in the last two years that suggest psilocybin promotes neuronal plasticity, which may lead to changes in brain network connectivity. Recent advancements in clinical trials using pure psilocybin in therapy suggest that it may effectively relieve the symptoms of depression in patients diagnosed with major depressive disorder and treatment-resistant depression. Sophisticated cellular and molecular experiments at the systems level have produced evidence that demonstrates psilocybin promotes neuritogenesis in the mouse brain - a mechanism that may address the root cause of depression at the cellular level. Finally, studies with psilocybin therapy for major depressive disorder suggest that this ancient molecule can promote functionally connected intrinsic networks in the human brain, resulting in durable improvements in the severity of depressive symptoms. Although further research is necessary, the prospect of using psilocybin for the treatment of mental illness is an enticing possibility.

Psilocybin-Induced Mystical-Type Experiences are Related to Persisting Positive Effects: A Quantitative and Qualitative Report

Psychedelic drugs such as psilocybin have shown substantial promise for the treatment of several psychiatric conditions including mood and addictive disorders. They also have the remarkable property of producing persisting positive psychological changes in healthy volunteers for at least several months. In this study (NCT03289949), 35 medium-high doses of psilocybin were administered to 28 healthy volunteers (12 females). By the end of the dosing day, participants reported the intensity of their acute experience using the 30-item Mystical Experience Questionnaire (MEQ) and an open-form qualitative report from home. Persisting psychological effects attributed to the psilocybin experience were measured using the Persisting Effects Questionnaire (PEQ) 3-months after administration. Using a linear latent-variable model we show that the MEQ total score is positively associated with the later emergence of positive PEQ effects (p = 3 × 10⁻⁵). Moreover, the MEQ subscales “Positive Mood” (p_corr = 4.1 × 10⁻⁴) and “Mysticality” (p_corr = 2.0 × 10⁻⁴) are associated with positive PEQ whereas the subscales “Transcendence of Time and Space” (p_corr = 0.38) and “Ineffability” (p_corr = 0.45) are not. Using natural language pre-processing, we provide the first qualitative descriptions of the “Complete Mystical Experience” induced by orally administered psilocybin in healthy volunteers, revealing themes such as a sense of connection with the Universe, familial love, and the experience of profound beauty. Combining qualitative and quantitative methods, this paper expands understanding of the acute psilocybin induced experience in healthy volunteers and suggests an importance of the type of experience in predicting lasting positive effects.

Predictors and potentiators of psychedelic-occasioned mystical experiences

Mystical experiences are often described as being among the most profound and meaningful events of a person’s life. Their occurrence, while a normal but uncommon phenomenon, is reliably occasioned by psychedelic substances under the appropriate conditions, although care is needed around the context of usage to help ensure safe and beneficial experiences. The occurrence of mystical experiences in psychedelic sessions is a key mediator of the sustained psychological benefits reported in both healthy and clinical populations. Certain factors including set and setting, drug dosage, trait absorption, drug type, intention and states of surrender and acceptance all predict or influence the occurrence of mystical experiences. Various additional factors may further contribute to the occurrence and intensity of mystical experiences and enhance their long-term benefits, including music, meditation and spiritual practices and nature-based settings. This review examines these factors and considers how they might be optimised to increase the chances of a mystical experience occurring, while also considering factors that are negatively associated with mystical experiences with suggestions on how these might be mitigated where applicable. Finally, potential future research avenues for furthering our knowledge of psychedelic mystical experiences and how their benefits might be enhanced is suggested. Maximising the potential for the occurrence of mystical experiences is an important aspect of the beneficial application of psychedelics.

Classic Psychedelic Drugs: Update on Biological Mechanisms

Renewed interest in the effects of psychedelics in the treatment of psychiatric disorders warrants a better understanding of the neurobiological mechanisms underlying the effects of these substances. During the past two decades, state-of-the-art studies of animals and humans have yielded new important insights into the molecular, cellular, and systems-level actions of psychedelic drugs. These efforts have revealed that psychedelics affect primarily serotonergic receptor subtypes located in cortico-thalamic and cortico-cortical feedback circuits of information processing. Psychedelic drugs modulate excitatory-inhibitory balance in these circuits and can participate in neuroplasticity within brain structures critical for the integration of information relevant to sensation, cognition, emotions, and the narrative of self. Neuroimaging studies showed that characteristic dimensions of the psychedelic experience obtained through subjective questionnaires as well as alterations in self-referential processing and emotion regulation obtained through neuropsychological tasks are associated with distinct changes in brain activity and connectivity patterns at multiple-system levels. These recent results suggest that changes in self-experience, emotional processing, and social cognition may contribute to the potential therapeutic effects of psychedelics.

Safety pharmacology of acute LSD administration in healthy subjects

RATIONALE

Lysergic acid diethylamide (LSD) is used in psychiatric and psychological research and investigated as a potential treatment for medical and psychiatric disorders, including depression, anxiety, and cluster headache.

OBJECTIVES

Safety data on clinical safety are available from small studies but not from larger samples. We report safety pharmacology data from a large pooled study sample on acute effects of LSD in healthy subjects.

METHODS

We conducted a pooled analysis of four double-blind, randomized, placebo-controlled, crossover studies that included a total of 83 healthy subjects and 131 single-dose administrations of LSD. LSD administrations were matched to dose groups according to measured LSD peak plasma concentrations to adjust for uncertainties in the correct LSD dose in some studies. Single doses were 25, 50, 100, and 200 µg of LSD base. We investigated subjective effects (self-rated any drug effect, good drug effect, bad drug effect, and anxiety), blood pressure, heart rate, body temperature, duration of the acute LSD response, acute (12 h) and subacute (24 h) adverse effects, reports of flashbacks, and liver and kidney function before and after the studies.

RESULTS

LSD dose-dependently increased subjective, physiologic, and adverse effects. The dose-response curves for the proportions of subjects with a certain amount of a subjective effect were steeper and reached a higher maximum for positive acute subjective effects compared with negative acute subjective effects. Maximal ratings of > 50% good drug effects were reached in 37%, 91%, 96%, and 91% of the LSD administrations at 25, 50, 100, and 200 µg. Maximal ratings of > 50% bad drug effects were reached in 0%, 9%, 27%, 31% at 25, 50, 100, and 200 µg, respectively. Mean ratings of Oceanic Boundlessness were 10%, 25%, 41%, and 44%, and mean ratings of Anxious Ego-Dissolution were 3.4%, 13%, 20%, and 22% at 25, 50, 100, and 200 µg, respectively. The physiologic effects of LSD were moderate. None of the subjects had systolic blood pressure > 180 mmHg at any time. Peak heart rate > 100 beats/min was observed in 0%, 6%, 20%, and 25% of the subjects at 25, 50, 100, and 200 µg, respectively. Maximal heart rates of 129 and 121 beats/min were observed in one subject at the 50 and 200 µg doses, respectively. Peak body temperature > 38° was observed in 0%, 11%, 7%, and 34% at 25, 50, 100, and 200 µg, respectively. Mean acute adverse effect scores on the List of Complaints were 5.6, 9.2, 12, and 13 at 25, 50, 100, and 200 µg, respectively. Kidney and liver function parameters were unaltered. Six subjects reported transient flashback phenomena.

CONCLUSIONS

The single-dose administration of LSD is safe in regard to acute psychological and physical harm in healthy subjects in a controlled research setting.

Psychedelic Therapy's Transdiagnostic Effects: A Research Domain Criteria (RDoC) Perspective

Accumulating clinical evidence shows that psychedelic therapy, by synergistically combining psychopharmacology and psychological support, offers a promising transdiagnostic treatment strategy for a range of disorders with restricted and/or maladaptive habitual patterns of emotion, cognition and behavior, notably, depression (MDD), treatment resistant depression (TRD) and addiction disorders, but perhaps also anxiety disorders, obsessive-compulsive disorder (OCD), Post-Traumatic Stress Disorder (PTSD) and eating disorders. Despite the emergent transdiagnostic evidence, the specific clinical dimensions that psychedelics are efficacious for, and associated underlying neurobiological pathways, remain to be well-characterized. To this end, this review focuses on pre-clinical and clinical evidence of the acute and sustained therapeutic potential of psychedelic therapy in the context of a transdiagnostic dimensional systems framework. Focusing on the Research Domain Criteria (RDoC) as a template, we will describe the multimodal mechanisms underlying the transdiagnostic therapeutic effects of psychedelic therapy, traversing molecular, cellular and network levels. These levels will be mapped to the RDoC constructs of negative and positive valence systems, arousal regulation, social processing, cognitive and sensorimotor systems. In summarizing this literature and framing it transdiagnostically, we hope we can assist the field in moving toward a mechanistic understanding of how psychedelics work for patients and eventually toward a precise-personalized psychedelic therapy paradigm.

Dosing Psychedelics and MDMA

Classic psychedelics, including psilocybin, lysergic acid diethylamide (LSD), dimethyltryptamine, and mescaline, and entactogens/empathogens, especially 3,4-methylenedioxymethamphetamine, have received renewed attention in psychiatric research and may be developed into medications for such indications as anxiety, depression, cluster headache, and posttraumatic stress disorder, among others. However, identifying proper doses is crucial. Controlled study data on dosing using well-characterized pharmaceutical formulations of the substances are scarce. The dose equivalence of different substances, dose-response effects, and subjective effects of different doses are of great interest and practically important for their clinical use in psychotherapy. Furthermore, the so-called microdosing of psychedelics has recently gained popularity, and the first placebo-controlled studies of LSD have been published. This chapter discusses different aspects of psychedelic dosing, including pharmaceutical aspects, definitions and characteristics of different doses, including microdoses, aspects of personalized dosing, and non-pharmacological factors, that can influence the response to psychedelics.

Altered states phenomena induced by visual flicker light stimulation

Flicker light stimulation can induce short-term alterations in consciousness including hallucinatory color perception and geometric patterns. In the study at hand, the subjective experiences during 3 Hz and 10 Hz stroboscopic light stimulation of the closed eyes were assessed. In a within-subjects design (N = 24), we applied the Positive and Negative Affect Schedule (mood state), time perception ratings, the Altered State of Consciousness Rating Scale, and the Phenomenology of Consciousness Inventory. Furthermore, we tested for effects of personality traits (NEO Five-Factor Inventory-2 and Tellegen Absorption Scale) on subjective experiences. Such systematic quantification improves replicability, facilitates comparisons between pharmacological and non-pharmacological techniques to induce altered states of consciousness, and is the prerequisite to study their underlying neuronal mechanisms. The resulting data showed that flicker light stimulation-induced states were characterized by vivid visual hallucinations of simple types, with effects strongest in the 10 Hz condition. Additionally, participants' personality trait of Absorption scores highly correlated with the experienced alterations in consciousness. Our data demonstrate that flicker light stimulation is capable of inducing visual effects with an intensity rated to be similar in strength to effects induced by psychedelic substances and thereby support the investigation of potentially shared underlying neuronal mechanisms.

Bridging the Gap? Altered Thalamocortical Connectivity in Psychotic and Psychedelic States

Psychiatry has a well-established tradition of comparing drug-induced experiences to psychotic symptoms, based on shared phenomena such as altered perceptions. The present review focuses on experiences induced by classic psychedelics, which are substances capable of eliciting powerful psychoactive effects, characterized by distortions/alterations of several neurocognitive processes (e.g., hallucinations). Herein we refer to such experiences as psychedelic states. Psychosis is a clinical syndrome defined by impaired reality testing, also characterized by impaired neurocognitive processes (e.g., hallucinations and delusions). In this review we refer to acute phases of psychotic disorders as psychotic states. Neuropharmacological investigations have begun to characterize the neurobiological mechanisms underpinning the shared and distinct neurophysiological changes observed in psychedelic and psychotic states. Mounting evidence indicates changes in thalamic filtering, along with disturbances in cortico-striato-pallido-thalamo-cortical (CSPTC)-circuitry, in both altered states. Notably, alterations in thalamocortical functional connectivity were reported by functional magnetic resonance imaging (fMRI) studies. Thalamocortical dysconnectivity and its clinical relevance are well-characterized in psychotic states, particularly in schizophrenia research. Specifically, studies report hyperconnectivity between the thalamus and sensorimotor cortices and hypoconnectivity between the thalamus and prefrontal cortices, associated with patients' psychotic symptoms and cognitive disturbances, respectively. Intriguingly, studies also report hyperconnectivity between the thalamus and sensorimotor cortices in psychedelic states, correlating with altered visual and auditory perceptions. Taken together, the two altered states appear to share clinically and functionally relevant dysconnectivity patterns. In this review we discuss recent findings of thalamocortical dysconnectivity, its putative extension to CSPTC circuitry, along with its clinical implications and future directions.