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A single dose of psilocybin, a psychedelic that acutely causes distortions of space-time perception and ego dissolution, produces rapid and persistent therapeutic effects in human clinical trials1-4. In animal models, psilocybin induces neuroplasticity in cortex and hippocampus5-8. It remains unclear how human brain network changes relate to subjective and lasting effects of psychedelics. Here we tracked individual-specific brain changes with longitudinal precision functional mapping (roughly 18 magnetic resonance imaging visits per participant). Healthy adults were tracked before, during and for 3 weeks after high-dose psilocybin (25 mg) and methylphenidate (40 mg), and brought back for an additional psilocybin dose 6-12 months later. Psilocybin massively disrupted functional connectivity (FC) in cortex and subcortex, acutely causing more than threefold greater change than methylphenidate. These FC changes were driven by brain desynchronization across spatial scales (areal, global), which dissolved network distinctions by reducing correlations within and anticorrelations between networks. Psilocybin-driven FC changes were strongest in the default mode network, which is connected to the anterior hippocampus and is thought to create our sense of space, time and self. Individual differences in FC changes were strongly linked to the subjective psychedelic experience. Performing a perceptual task reduced psilocybin-driven FC changes. Psilocybin caused persistent decrease in FC between the anterior hippocampus and default mode network, lasting for weeks. Persistent reduction of hippocampal-default mode network connectivity may represent a neuroanatomical and mechanistic correlate of the proplasticity and therapeutic effects of psychedelics.

Recent clinical trials have found that the serotonergic psychedelic psilocybin effectively alleviates anxiodepressive symptoms in patients with life-threatening illnesses when given in a supportive environment. These outcomes prompted Canada to establish legal pathways for therapeutic access to psilocybin, coupled with psychological support. Despite over one-hundred Canadians receiving compassionate access since 2020, there has been little examination of these real-world patients. We conducted a prospective longitudinal survey which focused on Canadians who were granted Section 56 exemptions for legal psilocybin-assisted psychotherapy. Surveys assessing various symptom dimensions were conducted at baseline, two weeks following the session (endpoint), and optionally one day post-session. Participant characteristics were examined using descriptive statistics, and paired sample t-tests were used to quantify changes from baseline to the two-week post-treatment endpoint. Eight participants with Section 56 exemptions (four females, Mage = 52.3 years), all with cancer diagnoses, fully completed baseline and endpoint surveys. Significant improvements in anxiety and depression symptoms, pain, fear of COVID-19, quality of life, and spiritual well-being were observed. Attitudes towards death, medical assistance in dying, and desire for hastened death remained unchanged. While most participants found the psilocybin sessions highly meaningful, if challenging, one reported a substantial decrease in well-being due to the experience. These preliminary data are amongst the first to suggest that psilocybin-assisted psychotherapy can produce psychiatric benefits in real-world patients akin to those observed in clinical trials. Limited enrollment and individual reports of negative experiences indicate the need for formal real-world evaluation programs to surveil the ongoing expansion of legal access to psychedelics.

There has been renewed interest in the use of 3,4-methylenedioxy-methamphetamine (MDMA) and serotonergic psychedelics in the treatment of multiple psychiatric disorders. Many of these compounds are known to produce prosocial effects, but how these effects relate to therapeutic efficacy and the extent to which prosocial effects are unique to a particular drug class is unknown. In this article, we present a narrative overview and compare evidence for the prosocial effects of MDMA and serotonergic psychedelics to elucidate shared mechanisms that may underlie the therapeutic process. We discuss 4 categories of prosocial effects: altered self-image, responses to social reward, responses to negative social input, and social neuroplasticity. While both categories of drugs alter self-perception, MDMA may do so in a way that is less related to the experience of mystical-type states than serotonergic psychedelics. In the case of social reward, evidence supports the ability of MDMA to enhance responses and suggests that serotonergic psychedelics may also do so, but more research is needed in this area. Both drug classes consistently dampen reactivity to negative social stimuli. Finally, preclinical evidence supports the ability of both drug classes to induce social neuroplasticity, promoting adaptive rewiring of neural circuits, which may be helpful in trauma processing. While both MDMA and serotonergic psychedelics produce prosocial effects, they differ in the mechanisms through which they do this. These differences affect the types of psychosocial interventions that may work best with each compound.

BACKGROUND: There is growing evidence for the therapeutic effects of the psychedelic drug psilocybin for major depression. However, due to the lack of safety data on combining psilocybin with selective serotonin reuptake inhibitors (SSRIs) and serotonin-norepinephrine reuptake inhibitors (SNRIs) and concerns that there may be a negative interaction on efficacy, participants enrolling in psychedelic trials are usually required to discontinue SNRI/SNRIs prior to enrolling. AIMS: Using data from a recent clinical trial examining the comparative efficacy the psychedelic drug psilocybin (P) combined with approximately 20 h of psychological support to a 6-week (daily) course of the SSRI escitalopram plus matched psychological support for major depressive disorder, we explored the effects of discontinuing SSRI/SNRIs prior to study enrolment on study outcomes. METHODS: Exploratory post hoc analyses using linear mixed effects model were performed to investigate the discontinuation effect on various validated depression symptom severity scales and well-being. The impact of SSRI/SNRIs discontinuation on the acute psychedelic experience was also explored. RESULTS/OUTCOMES: In the psilocybin group, there was a reduced treatment effect on all outcome measures for SSRI/SNRIs discontinuers compared with unmedicated patients at trial entry. However, no effects of discontinuation on measures of the acute psychedelic experience were found. CONCLUSION: Discontinuation of SSRI/SNRIs before psilocybin might diminish response to treatment; however, as we did not test SSRI/SNRI continuation in our trial, we cannot infer such causation. Moreover, the exploratory nature of the analyses makes them hypothesis generating, and not confirmatory. A controlled trial of SSRI/SNRI discontinuation versus continuation prior to psilocybin is urgently required.

BACKGROUND: Reference to an intrinsic healing mechanism or an inner healer is commonplace amongst psychedelic drug-using cultures. The inner healer refers to the belief that psychedelic compounds, plants or concoctions have an intrinsically regenerative action on the mind and brain, analogous to intrinsic healing mechanisms within the physical body, for example, after sickness or injury. AIMS: Here, we sought to test and critique this idea by devising a single subjective rating item pertaining to perceived inner healing effects. METHODS: The item was issued to 59 patients after a single high (25 mg, n = 30) or placebo (1 mg, n = 29) dose of psilocybin in a double-blind randomised controlled trial of psilocybin for depression. RESULTS: Inner healer scores were higher after the high versus placebo dose of psilocybin (t = 3.88, p

Do psychedelics affect sexual functioning postacutely? Anecdotal and qualitative evidence suggests they do, but this has never been formally tested. While sexual functioning and satisfaction are generally regarded as an important aspect of human wellbeing, sexual dysfunction is a common symptom of mental health disorders. It is also a common side effect of selective serotonin reuptake inhibitors (SSRIs), a first line treatment for depression. The aim of the present paper was to investigate the post-acute effects of psychedelics on self-reported sexual functioning, combining data from two independent studies, one large and naturalistic and the other a smaller but controlled clinical trial. Naturalistic use of psychedelics was associated with improvements in several facets of sexual functioning and satisfaction, including improved pleasure and communication during sex, satisfaction with ones partner and physical appearance. Convergent results were found in a controlled trial of psilocybin therapy versus an SSRI, escitalopram, for depression. In this trial, patients treated with psilocybin reported positive changes in sexual functioning after treatment, while patients treated with escitalopram did not. Despite focusing on different populations and settings, this is the first research study to quantitively investigate the effects of psychedelics on sexual functioning. Results imply a potential positive effect on post-acute sexual functioning and highlight the need for more research on this.

Psilocybin, a serotonergic psychedelic, is being increasingly researched in clinical studies for the treatment of psychiatric disorders. The relatively lengthy duration of oral psilocybins acute effects (4-6 h) may have pragmatic and cost-effectiveness limitations. Here, we explored the effects of intravenous (IV) N,N-Dimethyltryptamine (DMT), a closely related, but faster-acting psychedelic intervention, on mental health outcomes in healthy volunteers. Data is reported from two separate analyses: (1) A comparison of mental health-related variables 1 week after 7, 14, 18, and 20 mg of IV DMT versus IV saline placebo (n = 13) and, (2) A prospective dataset assessing effects before versus 2 weeks after 20 mg of IV DMT (n = 17). Mental health outcomes included measures of depression severity (QIDS-SR16), trait anxiety (STAI-T), Neuroticism (NEO-FFI), wellbeing (WHO-5), meaning in life (MLQ), optimism (LOT-R), and gratitude (GQ-6). In both the prospective and placebo-controlled datasets, significant improvements in scores of depression were found 1-2 weeks after DMT administration. Significant reductions in trait Neuroticism were only found for the placebo-controlled sample. Finally, changes in depression and trait anxiety correlated with acute peak experiences (assessed via Oceanic Boundlessness). While the use of two separate cohorts in pooled analysis limits the generalizability of these correlational findings, these results suggest that DMT may reduce depressive symptomatology by inducing peak experiences. The short half-life of IV DMT and its potential for flexible dosing via controlled infusions makes it an appealing candidate for psychedelic medicine. Further research in clinical samples is needed to corroborate the therapeutic potential of DMT.

As a proposed mediator between stigma-related stressors and negative mental health outcomes, HIV-related shame has been predictive of increased rates of substance use and difficulties adhering to antiretroviral treatment among people with HIV. These downstream manifestations have ultimately impeded progress toward national goals to End the HIV Epidemic, in part due to limited success of conventional psychotherapies in addressing HIV-related shame. In a pilot clinical trial (N = 12), receipt of psilocybin-assisted group therapy was associated with a large pre-post decrease in HIV-related shame as measured by the HIV and Abuse Related Shame Inventory, with a median (IQR) change of - 5.5 (- 6.5, - 3.5) points from baseline to 3-months follow-up (Z = - 2.6, p = 0.009, r = - 0.75). A paradoxical exacerbation of sexual abuse-related shame experienced by two participants following receipt of psilocybin raises critical questions regarding the use of psilocybin therapy among patients with trauma. These preliminary findings carry potential significance for the future of HIV care.

BACKGROUND: Psilocybin Therapy (PT) is being increasingly studied as a psychiatric intervention. Personality relates to mental health and can be used to probe the nature of PTs therapeutic action. METHODS: In a phase 2, double-blind, randomized, active comparator controlled trial involving patients with moderate-to-severe major depressive disorder, we compared psilocybin with escitalopram, over a core 6-week trial period. Five-Factor model personality domains, Big Five Aspect Scale Openness aspects, Absorption, and Impulsivity were measured at Baseline, Week 6, and Month 6 follow-up. RESULTS: PT was associated with decreases in neuroticism (B = -0.63), introversion (B = -0.38), disagreeableness (B = -0.47), impulsivity (B = -0.40), and increases in absorption (B = 0.32), conscientiousness (B = 0.30), and openness (B = 0.23) at week 6, with neuroticism (B = -0.47) and disagreeableness (B = -0.41) remaining decreased at month 6. Escitalopram Treatment (ET) was associated with decreases in neuroticism (B = -0.38), disagreeableness (B = -0.26), impulsivity (B = -0.35), and increases in openness (B = 0.28) at week 6, with neuroticism (B = -0.46) remaining decreased at month 6. No significant between-condition differences were observed. CONCLUSIONS: Personality changes across both conditions were in a direction consistent with improved mental health. With the possible exception of trait absorption, there were no compelling between-condition differences warranting conclusions regarding a selective action of PT (v. ET) on personality; however, post-ET changes in personality were significantly moderated by pre-trial positive expectancy for escitalopram, whereas expectancy did not moderate response to PT.

We conducted a meta-analysis using individual participant data from three, two-dose psilocybin trials for depression (N = 102) with the aim of assessing the risk of symptom worsening. Clinically significant symptom worsening occurred for a minority of participants in the psilocybin and escitalopram conditions (∼10%) and for a majority of participants in the waitlist condition (63.6%). Using data from the two trials with control arms, the psilocybin arm showed a lower likelihood of symptom worsening versus waitlist, and no difference in the likelihood of symptom worsening versus escitalopram. The limitation of a relatively small sample size should be addressed in future studies.

Psilocybin and lysergic acid diethylamide (LSD) experiences can range from very positive to highly challenging (e.g., fear, grief, and paranoia). These challenging experiences contribute to hesitancy toward psychedelic-assisted psychotherapy among health care providers and patients. Co-use of 3,4-Methylenedioxy methamphetamine (MDMA) with psilocybin/LSD anecdotally reduces challenging experiences and enhances positive experiences associated with psilocybin/LSD. However, limited research has investigated the acute effects of co-use of MDMA and psilocybin/LSD. In a prospective convenience sample (N = 698) of individuals with plans to use psilocybin/LSD, we examined whether co-use of MDMA with psilocybin/LSD (n = 27) is associated with differences in challenging or positive experiences. Challenging experiences were measured using the Challenging Experiences Questionnaire and positive experiences were measured using the Mystical Experience Questionnaire and single-item measures of self-compassion, compassion, love, and gratitude. Potentially confounding variables were identified and included as covariates. Relative to psilocybin/LSD alone, co-use of psilocybin/LSD with a self-reported low (but not medium-high) dose of MDMA was associated with significantly less intense total challenging experiences, grief, and fear, as well as increased self-compassion, love and gratitude. Co-use of psilocybin/LSD and MDMA was not associated with differences in mystical-type experiences or compassion. Findings suggest co-use of MDMA with psilocybin/LSD may buffer against some aspects of challenging experiences and enhance certain positive experiences. Limitations include use of a convenience sample, small sample size, and non-experimental design. Additional studies (including controlled dose-response studies) that examine the effects and safety of co-administering MDMA with psilocybin/LSD (in healthy controls and clinical samples) are warranted and may assist the development of personalized treatments.

Anorexia nervosa (AN) is a deadly illness with no proven treatments to reverse core symptoms and no medications approved by the US Food and Drug Administration. Novel treatments are urgently needed to improve clinical outcomes. In this open-label feasibility study, 10 adult female participants (mean body mass index 19.7 kg m-2; s.d. 3.7) who met Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition (DSM-5) criteria for AN or pAN (partial remission) were recruited to a study conducted at an academic clinical research institute. Participants received a single 25-mg dose of synthetic psilocybin in conjunction with psychological support. The primary aim was to assess safety, tolerability and feasibility at post-treatment by incidences and occurrences of adverse events (AEs) and clinically significant changes in electrocardiogram (ECG), laboratory tests, vital signs and suicidality. No clinically significant changes were observed in ECG, vital signs or suicidality. Two participants developed asymptomatic hypoglycemia at post-treatment, which resolved within 24 h. No other clinically significant changes were observed in laboratory values. All AEs were mild and transient in nature. Participants qualitative perceptions suggest that the treatment was acceptable for most participants. Results suggest that psilocybin therapy is safe, tolerable and acceptable for female AN, which is a promising finding given physiological dangers and problems with treatment engagement. ClinicalTrials.gov identifier NCT04661514 .

BACKGROUND: In a recent clinical trial examining the comparative efficacy of psilocybin therapy (PT) versus escitalopram treatment (ET) for major depressive disorder, 14 of 16 major efficacy outcome measures yielded results that favored PT, but the Quick Inventory of Depressive Symptomatology, Self-Report, 16 items (QIDS-SR16) did not. AIMS: The present study aims to (1) rationally and psychometrically account for discrepant results between outcome measures and (2) to overcome psychometric problems particular to individual measures by re-examining between-condition differences in depressive response using all outcome measures at item-, facet-, and factor-levels of analysis. METHOD: Four depression measures were compared on the basis of their validity for examining differences in depressive response between PT and ET conditions. RESULTS/OUTCOMES: Possible reasons for discrepant findings on the QIDS-SR16 include its higher variance, imprecision due to compound items and whole-scale and unidimensional sum-scoring, vagueness in the phrasing of scoring options for items, and its lack of focus on a core depression factor. Reanalyzing the trial data at item-, facet-, and factor-levels yielded results suggestive of PTs superior efficacy in reducing depressed mood, anhedonia, and a core depression factor, along with specific symptoms such as sexual dysfunction. CONCLUSION/INTERPRETATION: Our results raise concerns about the adequacy of the QIDS-SR16 for measuring depression, as well as the practice of relying on individual scales that tend not to capture the multidimensional structure or core of depression. Using an alternative approach that captures depression more granularly and comprehensively yielded specific insight into areas where PT therapy may be particularly useful to patients and clinicians.

Psychedelic compounds have displayed antidepressant potential in both humans and rodents. Despite their promise, psychedelics can induce undesired effects that pose safety concerns and limit their clinical scalability. The rational development of optimized psychedelic-related medicines will require a full mechanistic understanding of how these molecules produce therapeutic effects. While the hallucinogenic properties of psychedelics are generally attributed to activation of serotonin 2A receptors (5-HT2ARs), it is currently unclear if these receptors also mediate their antidepressant effects as several nonhallucinogenic analogues of psychedelics with antidepressant-like properties have been developed. Moreover, many psychedelics exhibit promiscuous pharmacology, making it challenging to identify their primary therapeutic target(s). Here, we use a combination of pharmacological and genetic tools to demonstrate that activation of 5-HT2A receptors is essential for tryptamine-based psychedelics to produce antidepressant-like effects in rodents. Our results suggest that psychedelic tryptamines can induce hallucinogenic and therapeutic effects through activation of the same receptor.

BackgroundMusic listening is a staple and valued component of psychedelic therapy, and previous work has shown that psychedelics can acutely enhance music-evoked emotion.AimsThe present study sought to examine subjective responses to music before and after psilocybin therapy for treatment-resistant depression, while functional magnetic resonance imaging (fMRI) data was acquired.MethodsNineteen patients with treatment-resistant depression received a low oral dose (10 mg) of psilocybin, and a high dose (25 mg) 1 week later. fMRI was performed 1 week prior to the first dosing session and 1 day after the second. Two scans were conducted on each day: one with music and one without. Visual analogue scale ratings of music-evoked 'pleasure' plus ratings of other evoked emotions (21-item Geneva Emotional Music Scale) were completed after each scan. Given its role in musical reward, the nucleus accumbens (NAc) was chosen as region of interest for functional connectivity (FC) analyses. Effects of drug (vs placebo) and music (vs no music) on subjective and FC outcomes were assessed. Anhedonia symptoms were assessed pre- and post-treatment (Snaith-Hamilton Pleasure Scale).ResultsResults revealed a significant increase in music-evoked emotion following treatment with psilocybin that correlated with post-treatment reductions in anhedonia. A post-treatment reduction in NAc FC with areas resembling the default mode network was observed during music listening (vs no music).ConclusionThese results are consistent with current thinking on the role of psychedelics in enhancing music-evoked pleasure and provide some new insight into correlative brain mechanisms.

BackgroundPsilocybin is a serotonin type 2A (5-HT2A) receptor agonist and naturally occurring psychedelic. 5-HT2A receptor density is known to be associated with body mass index (BMI), however, the impact of this on psilocybin therapy has not been explored. While body weight-adjusted dosing is widely used, this imposes a practical and financial strain on the scalability of psychedelic therapy. This gap between evidence and practice is caused by the absence of studies clarifying the relationship between BMI, the acute psychedelic experience and long-term psychological outcomes.MethodData were pooled across three studies using a fixed 25 mg dose of psilocybin delivered in a therapeutic context to assess whether BMI predicts characteristics of the acute experience and changes in well-being 2 weeks later. Supplementing frequentist analysis with Bayes Factors has enabled for conclusions to be drawn regarding the null hypothesis.ResultsResults support the null hypothesis that BMI does not predict overall intensity of the altered state, mystical experiences, perceptual changes or emotional breakthroughs during the acute experience. There was weak evidence for greater 'dread of ego dissolution' in participants with lower BMI, however, further analysis suggested BMI did not meaningfully add to the combination of the other covariates (age, sex and study). While mystical-type experiences and emotional breakthroughs were strong predictors of improvements in well-being, BMI was not.ConclusionsThese findings have important implications for our understanding of pharmacological and extra-pharmacological contributors to psychedelic-assisted therapy and for the standardization of a fixed therapeutic dose in psychedelic-assisted therapy.

BackgroundPast research reports a positive relationship between experience with classic serotonergic psychedelics and nature relatedness (NR). However, these studies typically do not distinguish between different psychedelic compounds, which have a unique psychopharmacology and may be used in specific contexts and with different intentions. Likewise, it is not clear whether these findings can be attributed to substance use per se or unrelated variables that differentiate psychedelic users from nonusers.AimsThe present study was designed to determine the relative degree to which lifetime experience with different psychedelic substances is predictive of self-reported NR among psychedelic-experienced users.MethodsWe conducted a combined reanalysis of five independent datasets (N = 3817). Using standard and regularized regression analyses, we tested the relationship between degree of experience with various psychedelic substances (binary and continuous) and NR, both within a subsample of psychedelic-experienced participants as well as the complete sample including psychedelic-naïve participants.Results/outcomesAmong people experienced with psychedelics, only past use of psilocybin (versus LSD, mescaline, Salvia divinorum, ketamine, and ibogaine) was a reliable predictor of NR and its subdimensions. Weaker, less reliable results were obtained for the pharmacologically similar N,N-dimethyltryptamine (DMT). Results replicate when including psychedelic-naïve participants. In addition, among people exclusively experience with psilocybin, use frequency positively predicted NR.Conclusions/interpretationResults suggest that experience with psilocybin is the only reliable (and strongest) predictor of NR. Future research should focus on psilocybin when investigating effects of psychedelic on NR and determine whether pharmacological attributes or differences in user expectations/use settings are responsible for this observation.

RationaleA general feeling of disconnection has been associated with mental and emotional suffering. Improvements to a sense of connectedness to self, others and the wider world have been reported by participants in clinical trials of psychedelic therapy. Such accounts have led us to a definition of the psychological construct of 'connectedness' as 'a state of feeling connected to self, others and the wider world'. Existing tools for measuring connectedness have focused on particular aspects of connectedness, such as 'social connectedness' or 'nature connectedness', which we hypothesise to be different expressions of a common factor of connectedness. Here, we sought to develop a new scale to measure connectedness as a construct with these multiple domains. We hypothesised that (1) our scale would measure three separable subscale factors pertaining to a felt connection to 'self', 'others' and 'world' and (2) improvements in total and subscale WCS scores would correlate with improved mental health outcomes post psychedelic use.ObjectivesTo validate and test the 'Watts Connectedness Scale' (WCS).MethodsPsychometric validation of the WCS was carried out using data from three independent studies. Firstly, we pooled data from two prospective observational online survey studies. The WCS was completed before and after a planned psychedelic experience. The total sample of completers from the online surveys was N = 1226. Exploratory and confirmatory factor analysis were performed, and construct and criterion validity were tested. A third dataset was derived from a double-blind randomised controlled trial (RCT) comparing psilocybin-assisted therapy (n = 27) with 6 weeks of daily escitalopram (n = 25) for major depressive disorder (MDD), where the WCS was completed at baseline and at a 6-week primary endpoint.ResultsAs hypothesised, factor analysis of all WCS items revealed three main factors with good internal consistency. WCS showed good construct validity. Significant post-psychedelic increases were observed for total connectedness scores (η2 = 0.339, p

BackgroundOver the last two decades, a number of studies have highlighted the potential of psychedelic therapy. However, questions remain to what extend these results translate to naturalistic samples, and how contextual factors and the acute psychedelic experience relate to improvements in affective symptoms following psychedelic experiences outside labs/clinics. The present study sought to address this knowledge gap.AimHere, we aimed to investigate changes in anxiety and depression scores before versus after psychedelic experiences in naturalistic contexts, and how various pharmacological, extrapharmacological and experience factors related to outcomes.MethodIndividuals who planned to undergo a psychedelic experience were enrolled in this online survey study. Depressive symptoms were assessed at baseline and 2 and 4 weeks post-psychedelic experience, with self-rated Quick Inventory of Depressive Symptomatology (QIDS-SR-16) as the primary outcome. To facilitate clinical translation, only participants with depressive symptoms at baseline were included. Sample sizes for the four time points were N = 302, N = 182, N = 155 and N = 109, respectively.ResultsRelative to baseline, reductions in depressive symptoms were observed at 2 and 4 weeks. A medicinal motive, previous psychedelic use, drug dose and the type of acute psychedelic experience (i.e. specifically, having an emotional breakthrough) were all significantly associated with changes in self-rated QIDS-SR-16.ConclusionThese results lend support to therapeutic potential of psychedelics and highlight the influence of pharmacological and non-pharmacological factors in determining response. Mindful of a potential sample and attrition bias, further controlled and observational longitudinal studies are needed to test the replicability of these findings.

Psychedelics are increasingly being recognized for their potential to treat a wide range of brain disorders including depression, post-traumatic stress disorder (PTSD), and substance use disorder. Their broad therapeutic potential might result from an ability to rescue cortical atrophy common to many neuropsychiatric and neurodegenerative diseases by impacting neurotrophic factor gene expression, activating neuronal growth and survival mechanisms, and modulating the immune system. While the therapeutic potential of psychedelics has not yet been extended to neurodegenerative disorders, we provide evidence suggesting that approaches based on psychedelic science might prove useful for treating these diseases. The primary target of psychedelics, the 5-HT2A receptor, plays key roles in cortical neuron health and is dysregulated in Alzheimer's disease. Moreover, evidence suggests that psychedelics and related compounds could prove useful for treating the behavioral and psychological symptoms of dementia (BPSD). While more research is needed to probe the effects of psychedelics in models of neurodegenerative diseases, the robust effects of these compounds on structural and functional neuroplasticity and inflammation clearly warrant further investigation.

The research and use of psychedelic medicines to treat common mental health disorders has increased substantially in the past 2 decades. At the same time, knowledge is relatively uncommon among midwives regarding (1) the relative benefits of psychedelic-assisted therapy, (2) best practices associated with the delivery of psychedelic-assisted therapy, and (3) responsible integration of this potentially useful intervention into mental health treatment plans. The purpose of this review is to describe current applications of psychedelic medicines to treat common mental health disorders, to describe the current legal status of these medicines used in this context, and to explore the potential for midwifery practice in this area with further training. This article also addresses the disparities regarding LGBTQIA+ and BIPOC populations in relation to this topic and their historical exclusion from research and treatment access in this field.

Healthful behaviours such as maintaining a balanced diet, being physically active and refraining from smoking have major impacts on the risk of developing cancer, diabetes, cardiovascular diseases and other serious conditions. The burden of the so-called 'lifestyle diseases'-in personal suffering, premature mortality and public health costs-is considerable. Consequently, interventions designed to promote healthy behaviours are increasingly being studied, e.g., using psychobiological models of behavioural regulation and change. In this article, we explore the notion that psychedelic substances such as psilocybin could be used to assist in promoting positive lifestyle change conducive to good overall health. Psilocybin has a low toxicity, is non-addictive and has been shown to predict favourable changes in patients with depression, anxiety and other conditions marked by rigid behavioural patterns, including substance (mis)use. While it is still early days for modern psychedelic science, research is advancing fast and results are promising. Here we describe psychedelics' proposed mechanisms of action and research findings pertinent to health behaviour change science, hoping to generate discussion and new research hypotheses linking the two areas. Therapeutic models including psychedelic experiences and common behaviour change methods (e.g., Cognitive Behaviour Therapy, Motivational Interviewing) are already being tested for addiction and eating disorders. We believe this research may soon be extended to help promote improved diet, exercise, nature exposure and also mindfulness or stress reduction practices, all of which can contribute to physical and psychological health and well-being.

Psychedelics including lysergic acid diethylamide (LSD) and psilocybin temporarily alter subjective experience through their neurochemical effects. Serotonin 2a (5-HT2a) receptor agonism by these compounds is associated with more diverse (entropic) brain activity. We postulate that this increase in entropy may arise in part from a flattening of the brain's control energy landscape, which can be observed using network control theory to quantify the energy required to transition between recurrent brain states. Using brain states derived from existing functional magnetic resonance imaging (fMRI) datasets, we show that LSD and psilocybin reduce control energy required for brain state transitions compared to placebo. Furthermore, across individuals, reduction in control energy correlates with more frequent state transitions and increased entropy of brain state dynamics. Through network control analysis that incorporates the spatial distribution of 5-HT2a receptors (obtained from publicly available positron emission tomography (PET) data under non-drug conditions), we demonstrate an association between the 5-HT2a receptor and reduced control energy. Our findings provide evidence that 5-HT2a receptor agonist compounds allow for more facile state transitions and more temporally diverse brain activity. More broadly, we demonstrate that receptor-informed network control theory can model the impact of neuropharmacological manipulation on brain activity dynamics.

The objective of the current study was to investigate the associations between lifetime classic psychedelic use and cardiometabolic diseases. Using data from the National Survey on Drug Use and Health (2005-2014), the present study examined the associations between lifetime classic psychedelic use and two types of cardiometabolic disease: heart disease and diabetes. Respondents who reported having tried a classic psychedelic at least once in their lifetime had lower odds of heart disease in the past year (adjusted odds ratio (aOR) = 0.77 (0.65-0.92), p = .006) and lower odds of diabetes in the past year (adjusted odds ratio (aOR) = 0.88 (0.78-0.99), p = .036). Classic psychedelic use might be beneficial for cardiometabolic health, but more research is needed to investigate potential causal pathways of classic psychedelics on cardiometabolic diseases.

Psychedelic microdosing describes the ingestion of near-threshold perceptible doses of classic psychedelic substances. Anecdotal reports and observational studies suggest that microdosing may promote positive mood and well-being, but recent placebo-controlled studies failed to find compelling evidence for this. The present study collected web-based mental health and related data using a prospective (before, during and after) design. Individuals planning a weekly microdosing regimen completed surveys at strategic timepoints, spanning a core four-week test period. Eighty-one participants completed the primary study endpoint. Results revealed increased self-reported psychological well-being, emotional stability and reductions in state anxiety and depressive symptoms at the four-week primary endpoint, plus increases in psychological resilience, social connectedness, agreeableness, nature relatedness and aspects of psychological flexibility. However, positive expectancy scores at baseline predicted subsequent improvements in well-being, suggestive of a significant placebo response. This study highlights a role for positive expectancy in predicting positive outcomes following psychedelic microdosing and cautions against zealous inferences on its putative therapeutic value.

Serotonergic hallucinogens such as lysergic acid diethylamide (LSD) induce head twitches in rodents via 5-HT2A receptor activation. The goal of the present investigation was to determine whether a correlation exists between the potency of hallucinogens in the mouse head-twitch response (HTR) paradigm and their reported potencies in other species, specifically rats and humans. Dose-response experiments were conducted with phenylalkylamine and tryptamine hallucinogens in C57BL/6J mice, enlarging the available pool of HTR potency data to 41 total compounds. For agents where human data are available (n = 36), a strong positive correlation (r = 0.9448) was found between HTR potencies in mice and reported hallucinogenic potencies in humans. HTR potencies were also found to be correlated with published drug discrimination ED50 values for substitution in rats trained with either LSD (r = 0.9484, n = 16) or 2,5-dimethoxy-4-methylamphetamine (r = 0.9564, n = 21). All three of these behavioral effects (HTR in mice, hallucinogen discriminative stimulus effects in rats, and psychedelic effects in humans) have been linked to 5-HT2A receptor activation. We present evidence that hallucinogens induce these three effects with remarkably consistent potencies. In addition to having high construct validity, the HTR assay also appears to show significant predictive validity, confirming its translational relevance for predicting subjective potency of hallucinogens in humans. These findings support the use of the HTR paradigm as a preclinical model of hallucinogen psychopharmacology and in structure-activity relationship studies of hallucinogens. Future investigations with a larger number of test agents will evaluate whether the HTR assay can be used to predict the hallucinogenic potency of 5-HT2A agonists in humans. "This article is part of the special issue entitled 'Serotonin Research: Crossing Scales and Boundaries'.

Contemporary research with classic psychedelic drugs (e.g., lysergic acid diethylamide (LSD) and psilocybin) is indebted to the twentieth-century researchers and clinicians who generated valuable clinical knowledge of these substances through experimentation. Several recent reviews that highlight the contributions of this early literature have focused on psychedelic-assisted individual psychotherapy modalities. None have attempted to systematically identify and compile experimental studies of psychedelic-assisted group therapy. In therapeutic settings, psychedelics were often used to enhance group therapy for a variety of populations and clinical indications. We report on the results of a systematic review of the published literature in English and Spanish on psychedelic-assisted group therapies. Publications are characterized by their clinical approach, experimental method, and clinical outcomes. Given the renewed interest in the clinical use of psychedelic medicines, this review aims to stimulate hypotheses to be tested in future research on psychedelic-assisted psychotherapy, group process, and interpersonal functioning.

ObjectiveTo explore whether psilocybin with psychological support modulates personality parameters in patients suffering from treatment-resistant depression (TRD).MethodTwenty patients with moderate or severe, unipolar, TRD received oral psilocybin (10 and 25 mg, one week apart) in a supportive setting. Personality was assessed at baseline and at 3-month follow-up using the Revised NEO Personality Inventory (NEO-PI-R), the subjective psilocybin experience with Altered State of Consciousness (ASC) scale, and depressive symptoms with QIDS-SR16.ResultsNeuroticism scores significantly decreased while Extraversion increased following psilocybin therapy. These changes were in the direction of the normative NEO-PI-R data and were both predicted, in an exploratory analysis, by the degree of insightfulness experienced during the psilocybin session. Openness scores also significantly increased following psilocybin, whereas Conscientiousness showed trend-level increases, and Agreeableness did not change.ConclusionOur observation of changes in personality measures after psilocybin therapy was mostly consistent with reports of personality change in relation to conventional antidepressant treatment, although the pronounced increases in Extraversion and Openness might constitute an effect more specific to psychedelic therapy. This needs further exploration in future controlled studies, as do the brain mechanisms of postpsychedelic personality change.

RationalePrevious research suggests that classical psychedelic compounds can induce lasting changes in personality traits, attitudes and beliefs in both healthy subjects and patient populations.AimHere we sought to investigate the effects of psilocybin on nature relatedness and libertarian-authoritarian political perspective in patients with treatment-resistant depression (TRD).MethodsThis open-label pilot study with a mixed-model design studied the effects of psilocybin on measures of nature relatedness and libertarian-authoritarian political perspective in patients with moderate to severe TRD ( n=7) versus age-matched non-treated healthy control subjects ( n=7). Psilocybin was administered in two oral dosing sessions (10 mg and 25 mg) 1 week apart. Main outcome measures were collected 1 week and 7-12 months after the second dosing session. Nature relatedness and libertarian-authoritarian political perspective were assessed using the Nature Relatedness Scale (NR-6) and Political Perspective Questionnaire (PPQ-5), respectively.ResultsNature relatedness significantly increased ( t(6)=-4.242, p=0.003) and authoritarianism significantly decreased ( t(6)=2.120, p=0.039) for the patients 1 week after the dosing sessions. At 7-12 months post-dosing, nature relatedness remained significantly increased ( t(5)=-2.707, p=0.021) and authoritarianism remained decreased at trend level ( t(5)=-1.811, p=0.065). No differences were found on either measure for the non-treated healthy control subjects.ConclusionsThis pilot study suggests that psilocybin with psychological support might produce lasting changes in attitudes and beliefs. Although it would be premature to infer causality from this small study, the possibility of drug-induced changes in belief systems seems sufficiently intriguing and timely to deserve further investigation.

Disruptions in social decision-making are becoming evident in many psychiatric conditions. These are studied using paradigms investigating the psychological mechanisms underlying interpersonal interactions, such as the Ultimatum Game (UG). Rejection behaviour in the UG represents altruistic punishment - the costly punishment of norm violators - but the mechanisms underlying it require clarification. To investigate the psychopharmacology of UG behaviour, we carried out two studies with healthy participants, employing serotonergic agonists: psilocybin (open-label, within-participant design, N = 19) and 3,4-methylenedioxymethamphetamine (MDMA; placebo-controlled, double-blind, crossover design, N = 20). We found that both MDMA and psilocybin reduced rejection of unfair offers (odds ratio: 0.57 and 0.42, respectively). The reduction in rejection rate following MDMA was associated with increased prosociality (R2 = 0.26, p = 0.025). In the MDMA study, we investigated third-party decision-making and proposer behaviour. MDMA did not reduce rejection in the third-party condition, but produced an increase in the amount offered to others (Cohen's d = 0.82). We argue that these compounds altered participants' conceptualisation of 'social reward', placing more emphasis on the direct relationship with interacting partners. With these compounds showing efficacy in drug-assisted psychotherapy, these studies are an important step in the further characterisation of their psychological effects.

RationaleDepressed patients robustly exhibit affective biases in emotional processing which are altered by SSRIs and predict clinical outcome.ObjectivesThe objective of this study is to investigate whether psilocybin, recently shown to rapidly improve mood in treatment-resistant depression (TRD), alters patients' emotional processing biases.MethodsSeventeen patients with treatment-resistant depression completed a dynamic emotional face recognition task at baseline and 1 month later after two doses of psilocybin with psychological support. Sixteen controls completed the emotional recognition task over the same time frame but did not receive psilocybin.ResultsWe found evidence for a group × time interaction on speed of emotion recognition (p = .035). At baseline, patients were slower at recognising facial emotions compared with controls (p

RationaleRecent clinical trials are reporting marked improvements in mental health outcomes with psychedelic drug-assisted psychotherapy.ObjectivesHere, we report on safety and efficacy outcomes for up to 6 months in an open-label trial of psilocybin for treatment-resistant depression.MethodsTwenty patients (six females) with (mostly) severe, unipolar, treatment-resistant major depression received two oral doses of psilocybin (10 and 25 mg, 7 days apart) in a supportive setting. Depressive symptoms were assessed from 1 week to 6 months post-treatment, with the self-rated QIDS-SR16 as the primary outcome measure.ResultsTreatment was generally well tolerated. Relative to baseline, marked reductions in depressive symptoms were observed for the first 5 weeks post-treatment (Cohen's d = 2.2 at week 1 and 2.3 at week 5, both p

RATIONALE:Recent studies have supported the safety and efficacy of psychedelic therapy for mood disorders and addiction. Music is considered an important component in the treatment model, but little empirical research has been done to examine the magnitude and nature of its therapeutic role. OBJECTIVES:The present study assessed the influence of music on the acute experience and clinical outcomes of psychedelic therapy. METHODS:Semi-structured interviews inquired about the different ways in which music influenced the experience of 19 patients undergoing psychedelic therapy with psilocybin for treatment-resistant depression. Interpretative phenomenological analysis was applied to the interview data to identify salient themes. In addition, ratings were given for each patient for the extent to which they expressed "liking," "resonance" (the music being experienced as "harmonious" with the emotional state of the listener), and "openness" (acceptance of the music-evoked experience). RESULTS:Analyses of the interviews revealed that the music had both "welcome" and "unwelcome" influences on patients' subjective experiences. Welcome influences included the evocation of personally meaningful and therapeutically useful emotion and mental imagery, a sense of guidance, openness, and the promotion of calm and a sense of safety. Conversely, unwelcome influences included the evocation of unpleasant emotion and imagery, a sense of being misguided and resistance. Correlation analyses showed that patients' experience of the music was associated with the occurrence of "mystical experiences" and "insightfulness." Crucially, the nature of the music experience was significantly predictive of reductions in depression 1 week after psilocybin, whereas general drug intensity was not. CONCLUSIONS:This study indicates that music plays a central therapeutic function in psychedelic therapy.

Psilocybin with psychological support is showing promise as a treatment model in psychiatry but its therapeutic mechanisms are poorly understood. Here, cerebral blood flow (CBF) and blood oxygen-level dependent (BOLD) resting-state functional connectivity (RSFC) were measured with functional magnetic resonance imaging (fMRI) before and after treatment with psilocybin (serotonin agonist) for treatment-resistant depression (TRD). Quality pre and post treatment fMRI data were collected from 16 of 19 patients. Decreased depressive symptoms were observed in all 19 patients at 1-week post-treatment and 47% met criteria for response at 5 weeks. Whole-brain analyses revealed post-treatment decreases in CBF in the temporal cortex, including the amygdala. Decreased amygdala CBF correlated with reduced depressive symptoms. Focusing on a priori selected circuitry for RSFC analyses, increased RSFC was observed within the default-mode network (DMN) post-treatment. Increased ventromedial prefrontal cortex-bilateral inferior lateral parietal cortex RSFC was predictive of treatment response at 5-weeks, as was decreased parahippocampal-prefrontal cortex RSFC. These data fill an important knowledge gap regarding the post-treatment brain effects of psilocybin, and are the first in depressed patients. The post-treatment brain changes are different to previously observed acute effects of psilocybin and other 'psychedelics' yet were related to clinical outcomes. A 'reset' therapeutic mechanism is proposed.

Plant-based psychedelics, such as psilocybin, have an ancient history of medicinal use. After the first English language report on LSD in 1950, psychedelics enjoyed a short-lived relationship with psychology and psychiatry. Used most notably as aids to psychotherapy for the treatment of mood disorders and alcohol dependence, drugs such as LSD showed initial therapeutic promise before prohibitive legislature in the mid-1960s effectively ended all major psychedelic research programs. Since the early 1990s, there has been a steady revival of human psychedelic research: last year saw reports on the first modern brain imaging study with LSD and three separate clinical trials of psilocybin for depressive symptoms. In this circumspective piece, RLC-H and GMG share their opinions on the promises and pitfalls of renewed psychedelic research, with a focus on the development of psilocybin as a treatment for depression.

What is the level of consciousness of the psychedelic state? Empirically, measures of neural signal diversity such as entropy and Lempel-Ziv (LZ) complexity score higher for wakeful rest than for states with lower conscious level like propofol-induced anesthesia. Here we compute these measures for spontaneous magnetoencephalographic (MEG) signals from humans during altered states of consciousness induced by three psychedelic substances: psilocybin, ketamine and LSD. For all three, we find reliably higher spontaneous signal diversity, even when controlling for spectral changes. This increase is most pronounced for the single-channel LZ complexity measure, and hence for temporal, as opposed to spatial, signal diversity. We also uncover selective correlations between changes in signal diversity and phenomenological reports of the intensity of psychedelic experience. This is the first time that these measures have been applied to the psychedelic state and, crucially, that they have yielded values exceeding those of normal waking consciousness. These findings suggest that the sustained occurrence of psychedelic phenomenology constitutes an elevated level of consciousness - as measured by neural signal diversity.

Because of the ethical and regulatory hurdles associated with human studies, much of what is known about the psychopharmacology of hallucinogens has been derived from animal models. However, developing reliable animal models has proven to be a challenging task due to the complexity and variability of hallucinogen effects in humans. This chapter focuses on three animal models that are frequently used to test the effects of hallucinogens on unconditioned behavior: head twitch response (HTR), prepulse inhibition of startle (PPI), and exploratory behavior. The HTR has demonstrated considerable utility in the neurochemical actions of hallucinogens. However, the latter two models have clearer conceptual bridges to human phenomenology. Consistent with the known mechanism of action of hallucinogens in humans, the behavioral effects of hallucinogens in rodents are mediated primarily by activation of 5-HT2A receptors. There is evidence, however, that other receptors may play secondary roles. The structure-activity relationships (SAR) of hallucinogens are reviewed in relation to each model, with a focus on the HTR in rats and mice.

Ego-disturbances have been a topic in schizophrenia research since the earliest clinical descriptions of the disorder. Manifesting as a feeling that one's "self," "ego," or "I" is disintegrating or that the border between one's self and the external world is dissolving, "ego-disintegration" or "dissolution" is also an important feature of the psychedelic experience, such as is produced by psilocybin (a compound found in "magic mushrooms"). Fifteen healthy subjects took part in this placebo-controlled study. Twelve-minute functional MRI scans were acquired on two occasions: subjects received an intravenous infusion of saline on one occasion (placebo) and 2 mg psilocybin on the other. Twenty-two visual analogue scale ratings were completed soon after scanning and the first principal component of these, dominated by items referring to "ego-dissolution", was used as a primary measure of interest in subsequent analyses. Employing methods of connectivity analysis and graph theory, an association was found between psilocybin-induced ego-dissolution and decreased functional connectivity between the medial temporal lobe and high-level cortical regions. Ego-dissolution was also associated with a "disintegration" of the salience network and reduced interhemispheric communication. Addressing baseline brain dynamics as a predictor of drug-response, individuals with lower diversity of executive network nodes were more likely to experience ego-dissolution under psilocybin. These results implicate MTL-cortical decoupling, decreased salience network integrity, and reduced inter-hemispheric communication in psilocybin-induced ego disturbance and suggest that the maintenance of "self"or "ego," as a perceptual phenomenon, may rest on the normal functioning of these systems.

Networks, as efficient representations of complex systems, have appealed to scientists for a long time and now permeate many areas of science, including neuroimaging (Bullmore and Sporns 2009 Nat. Rev. Neurosci. 10, 186-198. (doi:10.1038/nrn2618)). Traditionally, the structure of complex networks has been studied through their statistical properties and metrics concerned with node and link properties, e.g. degree-distribution, node centrality and modularity. Here, we study the characteristics of functional brain networks at the mesoscopic level from a novel perspective that highlights the role of inhomogeneities in the fabric of functional connections. This can be done by focusing on the features of a set of topological objects-homological cycles-associated with the weighted functional network. We leverage the detected topological information to define the homological scaffolds, a new set of objects designed to represent compactly the homological features of the correlation network and simultaneously make their homological properties amenable to networks theoretical methods. As a proof of principle,we apply these tools to compare resting state functional brain activity in 15 healthy volunteers after intravenous infusion of placebo and psilocybin-the main psychoactive component of magic mushrooms. The results show that the homological structure of the brain's functional patterns undergoes a dramatic change post-psilocybin, characterized by the appearance of many transient structures of low stability and of a small number of persistent ones that are not observed in the case of placebo.

The study of rapid changes in brain dynamics and functional connectivity (FC) is of increasing interest in neuroimaging. Brain states departing from normal waking consciousness are expected to be accompanied by alterations in the aforementioned dynamics. In particular, the psychedelic experience produced by psilocybin (a substance found in "magic mushrooms") is characterized by unconstrained cognition and profound alterations in the perception of time, space and selfhood. Considering the spontaneous and subjective manifestation of these effects, we hypothesize that neural correlates of the psychedelic experience can be found in the dynamics and variability of spontaneous brain activity fluctuations and connectivity, measurable with functional Magnetic Resonance Imaging (fMRI). Fifteen healthy subjects were scanned before, during and after intravenous infusion of psilocybin and an inert placebo. Blood-Oxygen Level Dependent (BOLD) temporal variability was assessed computing the variance and total spectral power, resulting in increased signal variability bilaterally in the hippocampi and anterior cingulate cortex. Changes in BOLD signal spectral behavior (including spectral scaling exponents) affected exclusively higher brain systems such as the default mode, executive control, and dorsal attention networks. A novel framework enabled us to track different connectivity states explored by the brain during rest. This approach revealed a wider repertoire of connectivity states post-psilocybin than during control conditions. Together, the present results provide a comprehensive account of the effects of psilocybin on dynamical behavior in the human brain at a macroscopic level and may have implications for our understanding of the unconstrained, hyper-associative quality of consciousness in the psychedelic state.

Psilocybin is a classic psychedelic and a candidate drug model of psychosis. This study measured the effects of psilocybin on resting-state network and thalamocortical functional connectivity (FC) using functional magnetic resonance imaging (fMRI). Fifteen healthy volunteers received intravenous infusions of psilocybin and placebo in 2 task-free resting-state scans. Primary analyses focused on changes in FC between the default-mode- (DMN) and task-positive network (TPN). Spontaneous activity in the DMN is orthogonal to spontaneous activity in the TPN, and it is well known that these networks support very different functions (ie, the DMN supports introspection, whereas the TPN supports externally focused attention). Here, independent components and seed-based FC analyses revealed increased DMN-TPN FC and so decreased DMN-TPN orthogonality after psilocybin. Increased DMN-TPN FC has been found in psychosis and meditatory states, which share some phenomenological similarities with the psychedelic state. Increased DMN-TPN FC has also been observed in sedation, as has decreased thalamocortical FC, but here we found preserved thalamocortical FC after psilocybin. Thus, we propose that thalamocortical FC may be related to arousal, whereas DMN-TPN FC is related to the separateness of internally and externally focused states. We suggest that this orthogonality is compromised in early psychosis, explaining similarities between its phenomenology and that of the psychedelic state and supporting the utility of psilocybin as a model of early psychosis.

Psychedelic drugs produce profound changes in consciousness, but the underlying neurobiological mechanisms for this remain unclear. Spontaneous and induced oscillatory activity was recorded in healthy human participants with magnetoencephalography after intravenous infusion of psilocybin--prodrug of the nonselective serotonin 2A receptor agonist and classic psychedelic psilocin. Psilocybin reduced spontaneous cortical oscillatory power from 1 to 50 Hz in posterior association cortices, and from 8 to 100 Hz in frontal association cortices. Large decreases in oscillatory power were seen in areas of the default-mode network. Independent component analysis was used to identify a number of resting-state networks, and activity in these was similarly decreased after psilocybin. Psilocybin had no effect on low-level visually induced and motor-induced gamma-band oscillations, suggesting that some basic elements of oscillatory brain activity are relatively preserved during the psychedelic experience. Dynamic causal modeling revealed that posterior cingulate cortex desynchronization can be explained by increased excitability of deep-layer pyramidal neurons, which are known to be rich in 5-HT2A receptors. These findings suggest that the subjective effects of psychedelics result from a desynchronization of ongoing oscillatory rhythms in the cortex, likely triggered by 5-HT2A receptor-mediated excitation of deep pyramidal cells.

Rationale: Although both psilocybin and dextromethorphan (DXM) produce psychedelic-like subjective effects, rates of non-medical use of psilocybin are consistently greater than DXM. Objective: New data are presented from a study of psilocybin and DXM relevant to understanding the features of psilocybin subjective effects that may account for its higher rates of non-medical use. Methods: Single, acute oral doses of psilocybin (10, 20, 30 mg/70 kg), DXM (400 mg/70 kg), and placebo were administered under double-blind conditions to 20 healthy participants with histories of hallucinogen use. Results: High doses of both drugs produced similar time courses and increases in participant ratings of peak overall drug effect strength. Nine subjective effect domains are proposed to be related to the reinforcing effects of psilocybin: liking, visual effects, positive mood, insight, positive social effects, increased awareness of beauty (both visual and music), awe/amazement, meaningfulness, and mystical experience. For most ratings, (1) psilocybin and DXM both produced effects significantly greater than placebo; (2) psilocybin showed dose-related increases; 3, DXM was never significantly higher than psilocybin; (4) the two highest psilocybin doses were significantly greater than DXM. These differences were consistent with two measures of desire to take the drug condition again. Conclusions: This analysis provides new information about domains of psilocybin subjective effects proposed to be related to its reinforcing effects (alternatively described as the "motivation" to use). Observed differences on these domains between psilocybin and DXM are consistent with the relative rates of non-medical use of psilocybin and DXM. [ABSTRACT FROM AUTHOR]