OPEN Foundation

J. Hallak

Polypharmacology or “Pharmacological Promiscuity” In Psychedelic Research: What Are We Missing?


Research with psychedelic drugs has mainly focused on isolated compounds. However, this approach is challenged by the “polypharmacology” paradigm. In this Viewpoint, we suggest that we may be missing something if we do not use the whole product in the case of ayahuasca or Psilocybe mushrooms. After describing how research on psychedelic drugs can be effectively combined with the polypharmacology paradigm, ethical issues are also briefly discussed.

Ona, G. S., Dos Santos, R. G., Hallak, J., & Bouso, J. C. (2020). Polypharmacology or “Pharmacological Promiscuity” In Psychedelic Research: What Are We Missing?. ACS chemical neuroscience, 11(20), 3191–3193.

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Therapeutic use of serotoninergic hallucinogens: A review of the evidence and of the biological and psychological mechanisms.


Serotoninergic hallucinogens include drugs such as lysergic acid diethylamide (LSD), dimethyltryptamine (DMT) and psilocybin. Recent trials with single/few doses of these compounds show that they induce rapid and sustained antidepressive, anxiolytic, and antiaddictive effects. These effects are also observed in religious groups using the DMT-containing brew ayahuasca. The agonist action of these substances on 5-HT2A receptors expressed in frontal and limbic areas increase glutamatergic transmission and neuroplasticity. These neurochemical effects are associated with acute alterations on self-perception and increases in introspection and positive mood, and with subacute and long-term decreases in psychiatric symptoms, increases in some personality traits such as openness, improvements in emotional processing, and increases in empathy. These are preliminary but promising results that should be further explored in controlled trials with larger sample sizes, especially considering that these compounds could be beneficial in the treatment of treatment-resistant psychiatric disorders.
dos Santos, R. G., & Hallak, J. E. C. (2019). Therapeutic use of serotoninergic hallucinogens: a review of the evidence and of the biological and psychological mechanisms. Neuroscience & Biobehavioral Reviews.,
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The Impact of Ayahuasca on Suicidality: Results From a Randomized Controlled Trial.


Suicide is a major public health problem. Given increasing suicide rates and limitations surrounding current interventions, there is an urgent need for innovative interventions for suicidality. Although ayahuasca has been shown to target mental health concerns associated with suicidality (i.e., depression and hopelessness), research has not yet explored the impact of ayahuasca on suicidality. Therefore, we conducted secondary analyses of a randomized placebo-controlled trial in which individuals with treatment-resistant depression were administered one dose of ayahuasca (n = 14) or placebo (n = 15). Suicidality was assessed by a trained psychiatrist at baseline, as well as 1 day, 2 days, and 7 days after the intervention. A fixed-effects linear mixed model, as well as between and within-groups Cohen’s d effect sizes were used to examine changes in suicidality. Controlling for baseline suicidality, we found a significant effect for time (p < .05). The effect of the intervention (i.e., ayahuasca vs. placebo) trended toward significance (p = .088). At all time points, we found medium between-group effect sizes (i.e., ayahuasca vs. placebo; day 1 Cohen’s d = 0.58; day 2 d = 0.56; day 7 d = 0.67), as well as large within-group (ayahuasca; day 1 Cohen’s d = 1.33; day 2 d = 1.42; day 7 d = 1.19) effect sizes, for decreases in suicidality. Conclusions: This research is the first to explore the impact of ayahuasca on suicidality. The findings suggest that ayahuasca may show potential as an intervention for suicidality. We highlight important limitations of the study, potential mechanisms, and future directions for research on ayahuasca as an intervention for suicidality. Clinical Trial Registration:, identifier NCT02914769.

Zeifman, R., Palhano-Fontes, F., Hallak, J., Nunes, E. A., Maia-de-Oliveira, J. P., & de Araujo, D. B. (2019). The Impact of Ayahuasca on Suicidality: Results From a Randomized Controlled Trial. Frontiers in Pharmacology10, 1325.
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Serotonergic hallucinogens/psychedelics could be promising treatments for depressive and anxiety disorders in end-stage cancer.


In a recent issue of the BMC Psychiatry, the evidence of effectiveness of treatments for psychiatric conditions in end-stage cancer patients was reviewed (Johnson, 2018). The review was comprehensive, and included traditional and non-traditional/alternative treatments, including herbal medicines and spirituality. However, evidence showing that classic or serotonergic hallucinogens/psychedelics such as psilocybin and lysergic acid diethylamide (LSD) could be effective treatments for depressive and anxiety disorders in end-stage cancer was not included. In this commentary, we expand the information available on the original article by briefly reviewing data from recent placebo-controlled, double-blind, cross-over clinical trials showing evidence that administration of single (or few) doses of LSD and psilocybin was associated with rapid and sustained reductions in depressive and anxiety symptoms in patients with end-stage cancer and other life-threatening diseases (e.g., Bechterew’s disease, Parkinson’s disease, Celiac disease). Since these substances seem to produce rapid and sustained therapeutic effects with single (or few) doses and well tolerated, large-scale, prospective, multi-site studies of end-stage cancer and classical/serotonergic hallucinogens/psychedelics should be performed to improve our understanding of the therapeutic potentials of these drugs and their use on clinical practice.
dos Santos, R. G., Bouso, J. C., & Hallak, J. E. (2019). Serotonergic hallucinogens/psychedelics could be promising treatments for depressive and anxiety disorders in end-stage cancer. BMC psychiatry19(1), 321.,
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Serotonergic hallucinogens and recognition of facial emotion expressions: a systematic review of the literature.


Recognition of emotions in facial expressions (REFE) is a key aspect of social cognition. Anxiety and mood disorders are associated with deficits in REFE, and anxiolytics and antidepressants reverse these deficits. Recent studies have shown that serotonergic hallucinogens (i.e. ayahuasca, dimethyltryptamine, psilocybin, lysergic acid diethylamide [LSD], and mescaline) have anxiolytic and antidepressant properties, but their effects on REFE are not well understood. The purpose of the study was to conduct a systematic review analyzing the effects of serotonergic hallucinogens on REFE in humans.
Studies published in the PubMed, PsycINFO, and Web of Science databases until 19 October 2018 which analyzed the effects of serotonergic hallucinogens on REFE in humans were included.
Of the 62 studies identified, 8 studies were included. Included studies involved the administration of a single or a few doses of LSD or psilocybin, and most trials were randomized and controlled with placebo. LSD and psilocybin reduced the recognition of negative emotions in most studies and modulated amygdala activity to these stimuli, which was correlated with antidepressive effects in patients. Both drugs were well tolerated.
Serotonergic hallucinogens reduced the recognition of negative emotions by modulating amygdala activity. Despite the small sample sizes, results suggest that serotonergic hallucinogens show promising beneficial effects on deficits in REFE.
Rocha, J. M., Osório, F. L., Crippa, J. A. S., Bouso, J. C., Rossi, G. N., Hallak, J. E., & dos Santos, R. G. (2019). Serotonergic hallucinogens and recognition of facial emotion expressions: a systematic review of the literature. Therapeutic advances in psychopharmacology9, 2045125319845774.,
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Possible Interactions Between 5-HT2A Receptors and the Endocannabinoid System in Humans: Preliminary Evidence of Interactive Effects of Ayahuasca and Endocannabinoids in a Healthy Human Subject


To the Editors

Ayahuasca is an ethnobotanical hallucinogenic preparation traditionally used for ritual and therapeutic purposes in the Northwestern Amazon Basin. It is prepared by the decoction of the bark of the vine Banisteriopsis caapi with the leaves of the shrub Psychotria viridisBanisteriopsis caapi contains the β-carbolines harmine, tetrahydroharmine, and harmaline, which are reversible inhibitors of monoamine oxidase type A (MAO-A), whereas P. viridis contains N,N-dimethyltryptamine (DMT), an agonist at 5-HT1A/2A/2C receptors. Pure DMT is not active orally because it is metabolized by MAO-A, but the β-carbolines in ayahuasca inhibit peripheral MAO-A and allow DMT to reach the brain. The β-carbolines also reach the systemic circulation in humans, but their effects are poorly characterized.

A recent randomized controlled trial (RCT) with 29 patients with treatment-resistant depression showed that, compared with placebo, a single ayahuasca dose induced significant antidepressant effects 7 days after drug intake. The mechanisms behind these effects are not clear but seem to involve agonism at cortical 5-HT2A receptors in brain areas related to emotional processing. 5-HT2A receptor activation also leads to the formation and release of endocannabinoids (ECs), and both the production and release of the EC 2-arachidonoylglycerol (2-AG) are induced by 5-HT2A agonists. Considering that the 5-HT2Areceptor and the EC system (ECS) are coexpressed in brain regions related to emotional processing, they could be involved in the antidepressive effect of ayahuasca. To test the possible interaction between both systems, we administered in an open-label design a single oral ayahuasca dose (1 mL/kg) to a healthy 34-year-old man and assessed subjective effects (Visual Analog Mood Scale [VAMS], Bodily Symptoms Scale, Beck Anxiety Inventory [BAI]), tolerability (blood pressure and heart rate, self-report), and EC plasma levels (anandamide [AEA], 2-AG) at several time points: VAMS, Bodily Symptoms Scale, blood pressure, and heart rate at baseline and 40, 90, 120, 150, and 240 minutes after drug intake; BAI–baseline, 240 minutes after drug intake; AEA, 2-AG (blood samples) at baseline and 90 and 240 minutes after drug intake. Analysis of the ayahuasca sample using gas chromatography with nitrogen-phosphorus detection showed the following alkaloid content (in mg/mL): 0.702 DMT, 1.748 harmine, 0.780 tetrahydroharmine, and 0.039 harmaline. Analysis of plasma ECs was performed using ultrahigh-performance liquid chromatography–tandem mass spectrometry. Detailed information on subjective measures and ayahuasca and EC analyses is described in the Supplemental Digital Content,

The volunteer was not taking any medication and was requested to abstain from alcohol, tobacco, and caffeinated drinks 12 hours before ayahuasca intake. He arrived in the laboratory at 7:00 AM under fasting conditions, and urinalysis for illicit drug use was performed before ayahuasca intake (the test measured cannabis and cocaine and was negative for both drugs). Afterward, a cannula was introduced in his arm for collecting blood samples. Ayahuasca was administered at approximately 8:00 AM, and the experimental session lasted 5 hours. The experimental session consisted in the administration of the drug followed by application of the scales and assessment of tolerability measures at the aforementioned time points. During measurements, the volunteer remained seated in a comfortable reclining chair in a quiet dimly lit room. There was no psychological intervention before, during, or after the session.The volunteer remained in the laboratory under observation to see if the effects had subsided and was discharged around 6 hours after drug intake, which is the approximate duration of the psychoactive effects of ayahuasca.

dos Santos, R. G., Crippa, J. A., de Lima Osório, F., Rocha, J. M., Rossi, G. N., Marchioni, C., … & Hallak, J. E. C. (2018). Possible Interactions Between 5-HT2A Receptors and the Endocannabinoid System in Humans: Preliminary Evidence of Interactive Effects of Ayahuasca and Endocannabinoids in a Healthy Human Subject. Journal of clinical psychopharmacology38(6), 644-646., 10.1097/JCP.0000000000000973
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Psychedelics and Personality.


In the past decade, an increasing number of clinical trials are reporting evidence that psychedelics or serotonergic hallucinogens (such as lysergic acid diethylamide, psilocybin, and ayahuasca/dimethyltryptamine) could be effective in the treatment of mood, anxiety, and substance use disorders. The mechanisms responsible for these effects are not fully understood but seem to involve changes in bran dynamics in areas rich in serotonergic 5-HT2A receptors and in personality. In the present text, we present a brief and critical overview of the current research in this field, pointing out both promises and limitations of these studies.
Aixalà, M., dos Santos, R. G., Hallak, J. E., & Bouso, J. C. (2018). Psychedelics and Personality.,
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Efficacy, tolerability, and safety of serotonergic psychedelics for the management of mood, anxiety, and substance-use disorders: a systematic review of systematic reviews


Mood, anxiety, and substance-use disorders are among the most prevalent psychiatric disorders in the population. Although several pharmacological treatments are available, they are not effective for a significant proportion of patients and are associated with several adverse reactions. Therefore, new treatments should be explored. Recent studies suggest that serotonergic hallucinogens/psychedelics including ayahuasca, psilocybin, and lysergic acid diethylamide (LSD) have anxiolytic, antidepressive, and antiaddictive effects. Areas Covered: A systematic review of systematic reviews assessing the efficacy, safety, and tolerability of serotonergic hallucinogens/psychedelic was performed using the PubMed data base until 11 April 2018. Systematic reviews with or without meta-analysis were analyzed, but only reviews that described at least one randomized controlled trial (RCT) were included. Expert Commentary: Psilocybin and LSD reduced anxiety and depression in cancer patients and symptoms of alcohol and tobacco dependence, and ayahuasca reduced depression symptoms in treatment-resistant depression. Although the results are promising, several studies were open label, and only few were RCTs, and most had small sample sizes and a short duration. Single or few doses of these drugs seem to be well tolerated, but long-term studies are lacking. New RCTs with bigger samples and longer duration are needed to replicate these findings.

dos Santos, R. G., Bouso, J. C., Alcázar-Córcoles, M. Á., & Hallak, J. E. (2018). Efficacy, tolerability, and safety of serotonergic psychedelics for the management of mood, anxiety, and substance-use disorders: A systematic review of systematic reviews. Expert review of clinical pharmacology11(9), 889-902., 10.1080/17512433.2018.1511424
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Serotonergic psychedelics and personality: A systematic review of contemporary research


Serotonergic psychedelics act as agonists at cortical 5-HT2A receptors and seem to induce personality changes. We conducted a systematic review of studies assessing the effects of these drugs on personality. Papers published from 1985–2016 were included from PubMed, LILACS, and SciELO databases. Three hundred and sixty-nine studies were identified, and 18 were included. Specific personality traits, such as Absorption and Self-Transcendence, seem to influence the effects of psychedelics, and psychedelic drug users and nonusers appear to differ in some personality traits. Psychedelics administered in controlled settings may induce personality changes, such as increased Openness and Self-Transcendence. Increases in global brain entropy induced by acute psychedelic administration predicted changes in Openness, and Self-Transcendence was negatively correlated with cortical thinning of the posterior cingulate cortex in long-term religious ayahuasca users. Acute and long-term use of psychedelics is associated with personality changes that appear to be modulated by 5-HT2A receptors. These changes seem to induce therapeutic effects that should be further explored in randomized controlled studies.

Bouso, J. C., dos Santos, R. G., Alcázar-Córcoles, M. Á., & Hallak, J. E. (2018). Serotonergic psychedelics and personality: a systematic review of contemporary research. Neuroscience & Biobehavioral Reviews. 10.1016/j.neubiorev.2018.02.004
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Ayahuasca: Psychological And Physiologic Effects, Pharmacology And Potential Uses In Addiction And Mental Illness


Ayahuasca, a traditional Amazonian decoction with psychoactive properties, is made from bark of the Banisteriopsis caapi vine (contains beta-carboline alkaloids) and leaves of the Psychotria viridis bush (supply the hallucinogen N,N-dimethyltryptamine (DMT)). Originally used by indigenous shamans for the purposes of spirit communication, magical experiences, healing, and religious rituals, across several South American countries ayahuasca has been incorporated into folk medicine and spiritual healing, and several Brazilian churches use it routinely to foster spiritual experience. More recently it is being used in Europe and North America, not only for religious or healing reasons, but also for recreation.
To review ayahuasca’s behavioral effects, possible adverse effects, proposed mechanisms of action and potential clinical uses in mental illness.
We searched Medline, in English, using the terms ayahuasca, dimethytryptamine, Banisteriopsis caapi, and Psychotria viridis and reviewed the relevant publications.
The following aspects of ayahuasca are summarized: Political and legal factors; acute and chronic psychological effects; electrophysiological studies and imaging; physiological effects, safety and adverse effects; pharmacology; potential psychiatric uses.
Many years of shamanic wisdom have indicated potential therapeutic uses for ayahuasca, and many present day studies suggest that it may be useful for treating various psychiatric disorders and addictions. The side effect profile appears to be relatively mild, but more detailed studies need to be done. Several prominent researchers feel that government regulations with regard to ayahuasca should be relaxed so that it could be provided more readily to recognized credible researchers to conduct comprehensive clinical trials.
Hamill, J., Hallak, J., Dursun, S. M., & Baker, G. (2018). Ayahuasca: Psychological And Physiologic Effects, Pharmacology And Potential Uses In Addiction And Mental Illness. Current neuropharmacology. 10.2174/1570159X16666180125095902
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