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Effects of Classical Psychedelics on Implicit and Explicit Emotional Empathy
and Cognitive Empathy: A Meta-analysis of MET task
Authors: Amit Olami1, Leehe Peled-Avron1,2
1Department of Psychology, Bar Ilan University, Ramat-Gan, Israel
.
2Gonda Multidisciplinary Brain Research Center.
Abstract
This meta-analysis investigates the effect of classic psychedelic drugs on empathy and
focuses on cognitive and emotional empathy measured using the Multifaceted
Empathy Test (MET). Empathy entails the ability to understand and share the feelings
of another and is a significant component of social interaction. Several studies have
examined the effects of psychedelic drugs such as LSD, psilocybin and ayahuasca on
empathy, yet their overall effect has not been studied so far. In this meta analysis, we
reviewed data from studies up to November 2023 with the aim of examining the
effects of various psychedelic drugs on empathic abilities broadly. Our findings
suggest that classical psychedelics significantly enhance explicit and implicit
emotional empathy without affecting measures of cognitive empathy. The results
emphasize the need to continue testing the therapeutic potential of classic psychedelic
drugs.
Introduction
Empathy is a complex psychological construct crucial for human interaction
and communication [1,2]. It encompasses various dimensions, including cognitive and
emotional empathy in implicit and explicit forms. Empathy is defined as the
understanding of a person from their frame of reference rather than one’s own, or
vicariously experiencing that person’s feelings, perceptions, and thoughts [3]
.
Empathy towards others can aid in creating more meaningful relationships and
enhance our social interactions [4]. Cognitive empathy, also known as the Theory of
Mind, involves the mental capacity to comprehend and process the thoughts and
emotions of others, enabling us to grasp different perspectives and foster mutual
understanding and respect in diverse interactions [5]. Emotional empathy, on the other
hand, goes beyond mere understanding to an emotional resonance, allowing us to
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share in the joy, sorrow, excitement, or pain of others, and is crucial for building
emotional bonds and providing comfort and support [6,7].
Emotional empathy can be further divided into implicit and explicit emotional
empathy. Implicit empathy, often referred to as “arousal,” includes the automatic,
unconscious aspect of emotional empathy in which the sharing of emotions arouses
the observing individual. In contrast, explicit emotional empathy is a deliberate and
conscious process requiring mental effort and conscious processing, enabling us to
respond appropriately and empathetically toward other people's emotions [3,8].
It is possible to change the levels of empathy with the help of various
psychological and biological interventions [9-11]. One such intervention pertains to
the use of classical psychedelics that can enhance empathic abilities. In recent years,
researchers have discovered an interest in the effects of psychedelic drugs on social
cognition in general and empathy in particular, and research has been done on the
impact of these drugs on various types of empathy. Classical psychedelics, including
Lysergic acid diethylamide (LSD), psilocybin, and ayahuasca, are all agonists at the
5-HT2A receptor, a serotonin receptor subtype [12,13]. These substances have shown
potential in addressing various psychiatric conditions, including depression and
anxiety [14-16], by breaking rigid mental patterns that are resistant to change [10,17].
LSD is derived from the ergot mushroom, leading to mood and perception changes at
doses of 100-200 micrograms
[18]. Psilocybin, derived from psilocybe mushrooms,
affects the brain by converting it into psilocin, inducing similar shifts in perception
and mood at doses of 20-25mg [19,20]. Ayahuasca, a South American brew
containing N, N-Dimethyltryptamine (DMT) and Monoamine oxidase inhibitors
(MAOIs), creates altered states of consciousness and vivid hallucinations [21,22].
Research presents diverse findings on psychedelics and empathy. LSD was
demonstrated to enhance emotional empathy and sociality [23]. Similarly, psilocybin
was found to increase emotional empathy [19,20] without affecting moral decision-
making [20] and increasing well-being and creativity [19]. Additional research
showed that ayahuasca increased cognitive empathy, emotional empathy, and well-
being up to one week after the ingestion during a ceremony [10,11]. Based on our
review of the professional literature, we have yet to find a meta-analysis that
synthesizes this literature and examines the overall effect of classical psychedelic
drugs on empathy. Therefore, our meta-analysis reviews recent studies in the field by
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synthesizing data from these studies on several types of empathy. These different
forms of empathy collectively influence how we interact, communicate, and build
relationships with others and how external factors, such as classical psychedelics use,
can impact these forms of empathy, highlighting the complex interplay between
psychological processes and biological mechanisms that underlie this social cognitive
function [23].
In the present meta-analysis, we will examine the existing research literature
on the effect of different classical psychedelics on a single task. We focused on the
multifaceted empathy test (MET), measuring cognitive and emotional empathy using
emotionally charged pictures. Meta-analyzing only one task across different studies
leads to a more accurate assessment, allows for direct comparison of results, and
provides deeper insights into specific factors associated with that task. It is especially
important when comparing several classical psychedelics that are administered in
different contexts with different doses and are measured at different times. We will
examine the effect of LSD, psilocybin and ayahuasca on cognitive empathy and
explicit and implicit emotional empathy to determine the effects of these classical
psychedelics on various types of empathy.
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Methods
This study followed the PRISMA reporting guidelines for systematic reviews
and meta-analysis
[24].
Search Strategy and inclusion criteria
From inception up to November 2023, a search for relevant articles was
conducted in the PubMed (Medline), PsycINFO, and Scopus bibliographic databases
using specific keywords: "LSD" OR “ayahuasca" OR “psychedelic” OR “lysergic
acid diethylamide” OR “Psilocybin” AND "empathy" OR "emotion" OR "social
cognition" OR "emotional empathy" OR "cognitive empathy" OR “implicit” OR
“explicit” OR “implicit emotional empathy” OR “explicit emotional empathy”, AND
“MET” OR “multifaceted empathy test”.
After a full-text review, if a study was deemed eligible, its reference list was
manually scrutinized for other relevant studies.
Initially, duplicate records were eliminated, and subsequently, the titles and
abstracts of the remaining publications were assessed. Any publications that did not
meet the inclusion criteria were excluded. The remaining publications were further
evaluated by thoroughly reviewing the full text. The inclusion criteria were then
applied again. To be considered for inclusion, studies had to meet the following
eligibility criteria: (1) they had to be original, peer-reviewed, full-text articles written
in English; (2) they had to involve healthy human participants; (3) they had to include
a single-dose or more of LSD or ayahuasca or psilocybin intervention; and (4) they
had to include an outcome(s) related to the MET tasks, provided that they met the
eligibility criteria mentioned above. Studies were excluded if they were reviews
and/or meta-analyses, included non-human subjects, assessed previous classic
psychedelics users retrospectively through self-report questionnaires, or were letters,
comments, abstracts, or conference papers. There were no exclusions based on the age
or sex of the subjects, classic psychedelics dose or frequency, administration routes,
or study size (Figure 1).
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Figure 1. The search and selection procedure was used to identify studies for
inclusion in this meta-analysis. Template provided by PRISMA (www.prisma-
statement.org).
Recorded measures and data extraction
The recorded variables included general information, such as the study's
authors, year of publication, number of subjects, and demographic variables, such as
age, gender, and classic psychedelic dosage and kinds of substance (Table 1). For the
calculation of effect sizes, means and standard deviations (SD) of the MET task
results were collected. If this information was not available in the publication or
provided by the authors, effect sizes were estimated using one of the following
methods: (1) by extracting mean and SD from published figures (using PlotDigitizer
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software, available at http://plotdigitizer.sourceforge.net), (2) based on F values, or
(3) based on p values.
Table 1 - demographic details on the included studies
Authors and year
Sample
size M/F
Mean age +
S.D Substance
Dosage
Dolder et al, 2016 22 12M,
12F 33 ± 11 LSD 100µg
Dolder et al, 2016 22 12M,
12F 33 ± 11 LSD 200µg
Thomas Pokorny et
al, 2017 32 17M,15F
26.72 ± 5.34
Psilocybin
0.215mg
Mason et al., 2019 55 29M,
26F 34.8 ± 8.9 Psilocybin
1.9mg
Uthaug, M et al,
2021 30
12M,
18F 40.18 ±
10.10 Ayahuasca
3.6±0.2mg
Kiraga et al, 2021 19 14M, 5F
39 ± 11.3 Ayahuasca
57.44 (±25.77)
mg
Statistical Analyses
The meta-analyses were conducted using the 'metaphor' package [25] in
RStudio version 2023.06.1 and Comprehensive Meta-Analysis (Version 3.3.070) [26].
Hedges' g was used to measure effect size. Hedges' g corrects for sample size bias and
is interpreted according to Cohen's D guidelines (0.2 for small effect, 0.5 for medium
effect, and 0.8 for large effect). Q statistic was used to evaluate heterogeneity across
studies based on the random effects model, as significant heterogeneity is expected in
meta-analyses of observational studies [27]. Q assesses the amount of observed
dispersion, and a statistically significant Q suggests that the studies do not share a
common true effect size. The I2 index was used to assess the proportion of total
variability in effect size estimates, with I2 values of approximately 25%, 50%, and
75% indicating low, moderate, and high heterogeneity, respectively. Publication bias
due to small study bias was quantitatively tested using Egger's regression test [28] for
each outcome. An Egger's test with a P value less than 0.05 indicated a small study
bias. Outlier and influence diagnostics were conducted to determine the impact of any
outliers and sensitivity re-analyses were performed without any identified outliers.
We gathered data for the MET task, which involved obtaining means and
standard deviations for three variables: (1) cognitive empathy, which measured the
accuracy (measured in percentage) in discerning emotions portrayed in the photos; (2)
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explicit emotional empathy, reflecting the participants' ratings indicating their level of
self-report explicit empathy towards the person in the photo; and (3) implicit
emotional empathy, indicating the arousal levels experienced while viewing the
photos.
Results
Classical Psychedelics effect on Cognitive empathy
Classical psychedelics did not affect cognitive empathy accuracy measures
compared to placebo or baseline measures across the included studies (studies: n=5
combined overall sample size: n = 128, Hedges’ g=-0.1153 95% CI from -2.0316 to
1.8010, p=0.9061, Z-value=-0.1179). Between-studies heterogeneity was significant
(Q = 36.7194, df = 5, I² = 87.34%, p < 0.0001) (Figure 2).
Publication Bias
No publication bias was found due to a small study effect, as indicated by
Egger's regression test (p = 0.5628). The funnel plot asymmetry tests, including
regression test (z = 0.5786, p = 0.5628) and rank correlation test (Tau = 0.1380, p =
0.7021), did not indicate significant publication bias or small-study effects.
The trim-and-fill analysis, aiming to assess the potential impact of publication
bias on the meta-analysis, revealed an estimated number of missing studies on the
right side of 3, with a standard error (SE) of 1.5812. This suggests that the asymmetry
observed in the funnel plot, indicative of potential publication bias, could have
affected other studies. Influence diagnostics did not identify any outliers.
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Figure 2. Forest Plot illustrates the influence of classical psychedelics
intervention on cognitive empathy scores measured by the MET task.
Classical psychedelics' Effect on Explicit Emotional empathy
Classical psychedelics were found to have a significant impact on explicit
emotional empathy compared to placebo or baseline measures across the included
studies (studies: n = 5; combined overall sample: n = 128, Hedges’ g = 0.7921, 95%
CI from 0.1786 to 1.4057, p = 0.0114, Z-value = 2.5304). Between-studies
heterogeneity was non-significant (Q = 1.1867, df = 5, I² = 0.00%, p < 0.9461)
(Figure 3).
Publication Bias
There was no significant publication bias. This is evidenced by the absence of
a small study effect, as indicated by Egger's regression test (p = 0.7800). The results
from the funnel plot asymmetry tests, including the regression test (z = -0.2793, p =
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0.7800) and the rank correlation test (Kendall's tau = -0.2760, p = 0.4442),
consistently do not show significant publication bias or small-study effects. Influence
diagnostics did not identify any outliers.
The trim-and-fill analysis, aiming to assess the potential impact of publication
bias on the meta-analysis, revealed an estimated number of missing studies on the
right side of 2, with a standard error (SE) of 1.7837. This suggests that the asymmetry
observed in the funnel plot, indicative of potential publication bias, could have
affected other studies. Influence diagnostics did not identify any outliers.
Figure 3. Forest Plot illustrates the influence of classical psychedelics
intervention on explicit emotional empathy scores measured by the MET
task.
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Classical psychedelics effect on Implicit emotional empathy
Classical psychedelics were found to have a statistically significant impact on
implicit emotional empathy ratings compared to placebo within the analyzed studies
(studies: n = 5; combined overall sample: n = 128, Hedges’ g = 0.7635, 95% CI from
-0.0191 to 1.5461, p = 0.05, Z-value = 1.9121).
The analysis revealed non-significant between-studies heterogeneity (Q =
0.4442, df = 5, I² = 0.00%, p < 0.9940) (Figure 4).
Publication Bias
Non significant publication bias was found, due to a small study effect as
indicated by Egger's regression test (p = 0.6427). The funnel plot asymmetry tests,
including the regression test (z =-0.4639, p = 0.6427) and The Rank Correlation Test
for Funnel Plot Asymmetry (Kendall's tau of -0.2000 with a p-value of 0.7194), did
not indicate significant publication bias or small-study effects.
The trim-and-fill analysis, aiming to assess the potential impact of publication
bias on the meta-analysis, revealed an estimated number of missing studies on the
right side of 3, with a standard error (SE) of 1.6385. This suggests that the asymmetry
observed in the funnel plot, indicative of potential publication bias, could have
affected other studies. Influence diagnostics did not identify any outliers.
was not certified by peer review) is the author/funder. All rights reserved. No reuse allowed without permission.
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Figure 4. Forest Plot illustrates the influence of classical psychedelics
intervention on implicit emotional empathy scores measured by the MET
task.
Discussion
The results of this meta-analysis indicate that classical psychedelics have a
significant impact on the levels of explicit and implicit emotional empathy but no
effect on cognitive empathy. The findings suggest that classic psychedelics may
influence the emotional components of empathy, while further research is necessary
to understand their impact on the cognitive components of empathy. There are several
potential interpretations of these results. When using psychedelic substances, users
have reported changes in perception [20], including hallucinations, subjective
perception of time and space and perception of the body [29]. Specifically, distorted
perception of the body might lead to blurring of the boundaries between self and
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other, which might lead to an increased ability to share the emotions of another, i.e.,
emotional empathy [4].
On a related note, psychedelic drugs can lead to a feeling of ego dissolution
[17]. Ego dissolution entails the dismantling of the experience of the ego [17] and is
accompanied by the lowering of the boundaries between the self and other people
[10,17]. At the neural level, ego dissolution has been linked to reduced alpha power in
the posterior cortex [30], which has been associated with increased emotional
empathy levels [31,32]. It is possible that due to the effect of psychedelic drugs on the
dissolution of the ego, there is an effect on emotional empathy, and this is due to an
increase in the ability to merge with another person and, through that, to understand
and share the feelings of others.
However, another mechanism through which classical psychedelics could
affect emotional empathy is personality traits. Psychedelics were found to increase the
personality trait of openness [33-36], and higher levels of openness have been
associated with higher levels of general empathy [37]. Thus, it is possible that through
an increase in openness to the experience of other individuals, the users can become
more emotionally empathic to their surroundings. To get a deeper understanding of
the relationship between psychedelics, empathy, and personality traits, further
research is necessary.
A similar pattern of results was also observed with 3,4-
methylenedioxymethamphetamine (MDMA), a compound with strong empathogenic
properties [38-39]. Specifically, MDMA was also found to enhance emotional, but not
cognitive, empathy [23,38]. Its action as a serotonin-enhancing agent shares common
neurochemical pathways with classical psychedelics' neural effects. This similarity
suggests a potential overlap in how these substances modulate social and emotional
processing, specifically through the enhancement of serotonin that affects emotional
empathy but not cognitive empathy. Future research targeting serotonergic effects
should determine the association between the enhancement of serotonin as a result of
either MDMA or classical psychedelics and an increase in emotional empathy.
Our meta-analysis used a comprehensive and systematic approach to gather
and analyze data. We examined the Multifaceted Empathy Test (MET), a
standardized tool to measure empathy, across various studies. The use of the MET
tool across all studies provided a consistent and specific measurement of empathy,
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enhancing the comparability and reliability of our results, which was the strength of
this meta-analysis.
Moreover, our meta-analysis has a high ecological value since we took into
consideration different settings and ways of administration of these substances.
Specifically, the setting of a ceremony in cases of an ayahuasca ceremony and
different physical, social and cultural environments in which the drug was taken may
change the mental experience of their effect [40]. For example, one study reported
that the ceremonies were held in a supportive group environment [10], which may
affect the experience of the participants positively and may have contributed to
improvements in the effect [41] compared to studies that examined the effects of the
substance on individuals who were alone or with a therapist when they were
administered the substance. Therefore, conducting a meta-analysis that analyzes
results across these different settings contributes to understanding the isolated effect
of these substances on empathy.
Moreover, the research includes different classical psychedelics, which
enables us to generalize beyond one specific substance. The way psychedelics are
reported in studies can be varied and complex due to differences in the types, doses,
and timing of administration. In our research, the sample sizes ranged from 19 to 55)
[11,19], ages from 25 to over 40 years [10,23], and dosage levels of psychedelics are
different and depend on the type of drugs.
These results offer new possibilities for therapeutic applications. Empathy is
crucial in psychotherapy because enhanced empathy can deepen the therapist-patient
connection and improve therapy outcomes [9]. Specifically in disorders characterized
by empathy deficits, such as certain personality disorders [20], psychedelics might aid
in developing better social skills and emotional connections. Indeed, early studies
suggested the use of psychedelic drugs as a treatment for criminals with antisocial
personality disorders and psychopaths [42-44].
Importantly, we would like to acknowledge that all of the studies examined in
this meta-analysis were done on healthy participants. Studying the effects of these
substances on clinical populations could provide valuable insights into their
therapeutic potential, such as depression and anxiety [14-16]. Moreover, to better
understand the neurological effects of psychedelics, it is important to examine their
acute and prolonged neural effect on empathy using imaging techniques such as
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electroencephalography (EEG) and functional magnetic resonance imaging (fMRI).
These methods will provide insight into the neurological correlates of the empathy-
enhancing effects of psychedelics.
Lastly, exploring individual differences in the subjective response to
psychedelics and addressing ethical considerations surrounding their use are also
crucial aspects of this field of research.
In conclusion, continued research on the effects of classical psychedelics on
empathy is necessary for understanding their complex effects and potential
therapeutic applications in fostering empathy and promoting prosocial behavior.
Continued research in this domain is not just a scientific imperative but also a moral
one, as it promises to look for new therapeutic modalities that could profoundly
benefit individuals and society at large.
Data Availability Statement
The datasets generated and/or analyzed during the current study are available from the
corresponding author upon request. All data supporting this study's findings are
contained within the article and in supplementary information files.
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