J Psychopharmacol
February 15, 2018
Robin L Carhart-Harris, Leor Roseman, Eline Haijen et al.
646 citations
Modern trials support the therapeutic potential of psychedelic drugs, but their effects are exceptionally sensitive to context—the combination of mindset and physical setting. This opinion piece highlights how classic psychedelics act through 5-HT2A receptor agonism and associated plasticity, making context crucial. It proposes a study design to test positive interactions between psychedelics and context, and presents new findings on how contextual determinants shape the quality of a psychedelic experience, which in turn predicts long-term mental health outcomes. The authors aim to inform good practice, optimize treatment models, and reduce stigma while building evidence that context minimizes harms and maximizes benefits.
J Psychopharmacol
July 11, 2019
Leor Roseman, Eline Haijen, Kelvin Idialu-Ikato et al.
415 citations
Emotional breakthrough—a sudden release or shift in emotion during a psychedelic experience—is a distinct and important component that predicts long-term psychological changes, separate from mystical-type experiences. A six-item Emotional Breakthrough Inventory was validated in 379 participants who completed surveys before and after a planned psychedelic experience. Emotional breakthrough scores were dose-dependent and higher when the psychedelic was taken with therapeutic intent. In a subsample of 75 participants with low baseline well-being, emotional breakthrough, mystical experience, and challenging experience scores together significantly predicted changes in well-being (r=0.45). Emotional breakthrough and mystical experience scores predicted increases in well-being, while challenging experience scores predicted smaller increases.
J Psychopharmacol
August 1, 2022
Victoria Amalie Nygart, Lis Marie Pommerencke, Eline Haijen et al.
73 citations
Depressive symptoms decreased two and four weeks after a psychedelic experience in a naturalistic, non-clinical setting. The study tracked a large group of people who planned to use psychedelics outside a lab or clinic, including only those with depressive symptoms at the start. A medicinal motive, prior psychedelic use, drug dose, and having an emotional breakthrough during the experience were all linked to greater symptom reductions. The authors note potential sample and attrition biases and call for further controlled and observational studies to confirm the findings.
Frontiers in Psychiatry
June 29, 2021
Keri Mans, Hannes Kettner, David Erritzøe et al.
65 citations
Psychedelic substances like LSD and psilocybin have regained legitimacy in clinical research. In this naturalistic observational study of volunteers intending to take a psychedelic, well-being was assessed using fourteen measures at four time points: 1 week before and 2 weeks, 4 weeks, and 2 years after the experience (sample sizes 654, 315, 212, and 64, respectively). Changes clustered into three factors: 'Being well,' 'Staying well,' and 'Spirituality.' Repeated measures analysis showed improvements in Being Well and Staying Well in the weeks following the experience, and mixed model analyses indicated these improvements remained statistically significant up to 2 years, despite high attrition. Spirituality did not show significant change.
Psychopharmacology (Berl)
November 4, 2021
Joanna Kuć, Hannes Kettner, Fernando Rosas et al.
37 citations
People who use cannabis at the same time as a classic psychedelic report more intense subjective effects, with higher cannabis doses linked to stronger mystical, visual, and ego-dissolution experiences. The relationship between cannabis dose and challenging experiences followed a U-shaped pattern, while emotional breakthrough showed no connection to cannabis dose. The findings suggest an interaction between cannabis and psychedelics, but the study's design cannot establish cause or clinical implications.
Journal of Medical Internet Research
May 4, 2021
Sebastian Hübner, Eline Haijen, Mendel Kaelen et al.
23 citations
In web-based studies that track people before and after they use psychedelics, many participants stop responding, which can bias the results. Analyzing data from 654 initial participants, younger age, lower education, higher extraversion, and lower conscientiousness predicted dropping out before the four-week endpoint. Neither positive attitudes toward psychedelics nor intense challenging experiences during the drug session predicted dropout. These attrition patterns match those seen in other long-term studies, suggesting they are not unique to psychedelic research. The absence of dropout linked to psychedelic advocacy or negative drug experiences reduces concerns about certain biases in this type of data.
Psychol Med
September 27, 2024
Michael Angyus, Sarah Osborn, Eline Haijen et al.
10 citations
A 9-item scale called the Imperial Psychedelic Predictor Scale (IPPS) can predict key features of the acute psychedelic experience. The scale has three factors: set (mindset), rapport (relationship with the guide or setting), and intention. In a controlled administration dataset, set and rapport together explained 40% of the variance in mystical experiences, while set alone explained 16% of the variance in challenging experiences. In another controlled dataset, rapport explained 9% of the variance in emotional breakthrough. The scale shows good internal consistency and predicts mystical, challenging, and emotional breakthrough experiences across naturalistic and controlled settings.
European Psychiatry
January 1, 2024
Eline Haijen, Petra P. M. Hurks, Kim P. C. Kuypers
10 citations
Adults with severe ADHD symptoms who microdosed psychedelics reported better emotion regulation and some empathy improvements in an initial uncontrolled study. A second study with a control group found that after four weeks, ADHD symptoms were lower in the microdosing group than in those taking conventional ADHD medication. However, only one emotion regulation measure—expressive suppression—remained improved after accounting for the control group. The findings suggest microdosing may help with ADHD symptoms and certain emotion regulation strategies, but there was no evidence for effects on empathy.
Psychopharmacology
November 16, 2017
Eline Haijen, Magı́ Farré, Rafael de la Torre et al.
9 citations
MDMA impaired verbal memory 90 minutes after administration in a word learning task, replicating earlier findings with the same dose (75 mg). Contrary to expectations, MDMA did not affect endocannabinoid concentrations (anandamide and 2-AG) in blood, and the 5-HT2 receptor blocker ketanserin did not block MDMA-induced memory impairment. Ketanserin alone increased AEA concentrations 180 minutes after administration. The findings suggest that peripherally measured endocannabinoids are not involved in the verbal memory deficit during MDMA intoxication.
Frontiers in Psychiatry
October 16, 2023
Eline Haijen, Petra P. M. Hurks, Kim P. C. Kuypers
6 citations
Adults with ADHD who microdosed psychedelics for four weeks showed increased trait mindfulness—specifically the ability to describe and not judge inner experiences—and decreased neuroticism, while other personality traits like conscientiousness, extraversion, agreeableness, and openness remained unchanged. These changes occurred regardless of whether participants also used conventional ADHD medication or had other mental health diagnoses. The findings suggest that microdosing may alter otherwise stable psychological traits in this population, though placebo-controlled studies are needed to confirm the effects.
Current Opinion in Psychology
August 6, 2025
Iva Totomanova, Eline Haijen, Petra P M Hurks et al.
5 citations
Regular use of low doses of LSD or psilocybin, known as microdosing, has been studied in 57 human studies. Reported benefits include improved mood, enhanced cognition, social functioning, and mental health, but findings are inconsistent and largely based on self-reports. Adverse effects such as anxiety, physical discomfort, and cognitive disruption are also common. Outcomes vary greatly by individual and are shaped by expectations, context, and baseline state. Experimental studies of single doses often yield null findings, while observational studies of repeated use report more benefits. The evidence remains inconclusive and warrants caution.
Psychoactives
March 31, 2024
Rishma S. I. Khubsing, Martin van Leerdam, Eline Haijen et al.
3 citations
Both an ayahuasca retreat and a breathwork session led to sustained increases in well-being, resilience, and self-compassion over 12 weeks, with no difference between the two groups. Older participants reported higher resilience and self-compassion overall. The ayahuasca group showed higher self-compassion and lower neuroticism than the breathwork group. Neuroticism decreased in both groups, and agreeableness increased over time regardless of group, while extraversion, conscientiousness, and openness did not change. The findings suggest that improvements in psychological processes may be influenced by the social setting rather than solely by the substance.
Sebastian Hübner, Eline Haijen, Mendel Kaelen et al.
2 citations
Younger age, lower educational levels, lower conscientiousness, and higher extraversion predict dropout in web-based prospective studies of psychedelic use. Baseline attitudes toward psychedelics and the intensity of acute challenging experiences do not predict attrition. These demographic and personality predictors align with those found in longitudinal research in other fields, suggesting that concerns about bias from psychedelic advocacy or negative drug experiences may be less problematic than previously thought.
PsyArXiv
February 13, 2024
Michael Angyus, Sarah Osborn, Eline Haijen et al.
1 citation
preprint
A new 9-item scale called the Imperial Psychedelic Predictor Scale (IPPS) predicts key features of the acute psychedelic experience. Analyzing four independent datasets (two online surveys with 741 and 836 participants, and two controlled administration studies with 30 and 28 participants), the scale showed good internal consistency and three factors: set, rapport, and intention. The IPPS significantly predicted mystical, challenging, and emotional breakthrough experiences. In one controlled dataset, set and rapport explained 40% of variance in mystical experience, and set alone explained 16% of variance in challenging experience. In another, rapport explained 9% of variance in emotional breakthrough. The scale may improve safety and therapeutic outcomes by forecasting response variability.
Journal of psychopharmacology (Oxford, England)
May 1, 2026
Otto Simonsson, Taylor Lyons, Joseph Marks et al.
Across three studies—a naturalistic observation, a single-arm psilocybin trial with healthy volunteers, and a randomized controlled trial comparing psilocybin to escitalopram in depressed patients—psychedelic use did not produce significant changes in authoritarian attitudes. Contrary to earlier suggestions, the evidence does not reliably show that psychedelics decrease authoritarian attitudes. Future work should use larger, more diverse samples and examine other political outcomes.
Journal of Psychedelic Studies
September 4, 2025
Giordano Novak Rossi, Rishma S. I. Khubsing, Eline Haijen et al.
Both a single ayahuasca ceremony and a single breathwork session led to lasting improvements in cognitive flexibility, emotion regulation, positive affect, and sleep quality over three months. Improvements in cognitive flexibility appeared before changes in emotion regulation, partially supporting the idea that cognitive shifts may drive later emotional gains. The two treatments did not differ in their overall benefits, and the role of participants' experience and motivation remains unclear. The findings suggest that both practices can promote psychological well-being, but further research is needed to clarify the mechanisms and temporal order of these effects.
Psychol Med
August 26, 2025
Michael Angyus, Sarah Osborn, Eline Haijen et al.
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