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. Author manuscript; available in PMC: 2026 Mar 18.
Published in final edited form as: Psychiatry Res. 2025 Jan 10;345:116359. doi: 10.1016/j.psychres.2025.116359

A Systematic Review of Participant Diversity in Psychedelic-Assisted Psychotherapy Trials

Stephanie L Haft 1,*, Amanda E Downey 1,2,*, Marissa Raymond-Flesch 2,3, Gisele Fernandes-Osterhold 1,4,5, Ellen R Bradley 1,6, Aoife O’Donovan 1,6, Joshua Woolley 1,6
PMCID: PMC12994433  NIHMSID: NIHMS2143479  PMID: 39823947

Abstract

Limited participant diversity in mental health intervention research perpetuates mental health disparities. This issue has become a particularly salient concern in studies of psychedelic-assisted psychotherapy (PAT), which is emerging as a promising mental health intervention. This systematic review evaluates the reporting, representation, and analysis of participant sociodemographic characteristics in randomized controlled trials (RCTs) of PAT. A total of 21 RCTs of psilocybin- and 3,4-methylenedioxy methamphetamine (MDMA)-assisted therapies (N = 1034) are summarized. Participants’ gender (100%) and race or ethnicity (76%) were frequently reported, with socioeconomic status (SES) sometimes (57%) reported using heterogeneous metrics. Sexual orientation (9.5%) and immigration status (4.8%) were rarely reported, and no studies reported gender identity. Compared to their representation in the US population and non-psychedelic clinical trials, Black/African-American participants (12.2%) and Hispanic/Latino participants (7.2%) were significantly underrepresented in PAT RCTs. MDMA trials enrolled more diverse participant samples than psilocybin trials. Analyses on treatment effects based on sociodemographic variables were virtually nonexistent. These findings underscore the need for more inclusive recruitment strategies, along with more rigorous reporting and analytic practices, to improve the generalizability of PAT research.

1. Introduction

Randomized controlled trials (RCTs) exploring the safety and efficacy of psychedelic-assisted psychotherapy (PAT) for mental health disorders yield promising outcome data (Ko et al., 2023; Wheeler & Dyer, 2020). In recent years, trials of psilocybin- and MDMA-assisted therapy have show one to three administrations of high-dose psychedelic compounds, combined with a brief course of psychotherapy, may improve symptoms across a range of mental health diagnoses (Carhart-Harris et al., 2018; Carhart-Harris & Goodwin, 2017; Luoma et al., 2020; Schlag et al., 2022). However, these RCTs have limited generalizability due to a lack of participant diversity. A previous review found that between 1993 and 2017, 82.3% of participants in clinical psychedelic studies identified as non-Hispanic White (Michaels et al., 2018a), highlighting the critical problem that people enrolling in trials do not adequately represent the population in need of treatment (Fogg et al., 2021; Ortiz et al., 2022; Simon, 2023; Smith et al., 2022; Viña & Stephens, 2023).

Individuals from minoritized demographic backgrounds experience chronic stress due to their marginalized status (Frost & Meyer, 2023) and disproportionately bear the burden of moderate to severe mental illness (Mongelli et al., 2020). Treatment approaches that do not acknowledge and address the specific stressors faced by these communities may be perceived as irrelevant or insensitive, influencing acceptability. Chronic stress as well as related structural factors such as poverty or distrust of medical institutions may also modulate the efficacy and feasibility of a treatment. Developing accessible psychedelic interventions that have real-world impact will therefore require engagement of representative populations in clinical research and rigorous examination of how demographic characteristics influence outcomes. Recent guidelines from federal agencies encouraging standardized, transparent reporting of demographic characteristics in RCTs (American Psychological Association, 2020; Moher et al., 2010; National Institute on Minority Health and Health Disparities, 2024; US Food and Drug Administration, 2022) indicate growing support for this view. Given the dramatic increase in psychedelic trials over the past 7 years, an updated and expanded systematic review is needed to (1) assess progress since 2017 and (2) evaluate participant demographic characteristics beyond race and ethnicity, as multiple forms of identity and marginalization impact treatment response and uptake (Cole, 2009a).

The overall goal of the present systematic review is to examine the reporting, representation, and moderating effects of participant demographic characteristics in extant PAT RCTs.

These are the pillars of investigation of participant diversity in RCTs (Polo et al., 2019). Unfortunately, recent reviews uncover poor sample characteristic reporting in RCTs for psychiatric conditions – for example, less than half of RCTs for depression report participant race or ethnicity (Polo et al., 2019), and less than 4% of RCTs for suicide and self-injury report participant sexual orientation (Maria Guzmán et al., 2024). Adequate representation in research is also a challenge. Participants that are low-income or are part of a minoritized group due to race, ethnicity, or sexual orientation are consistently underrepresented in RCTs targeting psychiatric conditions (Lolic et al., 2021) such as depression (Monahan et al., 2023; Polo et al., 2022), suicide and self-injury (Maria Guzmán et al., 2024), posttraumatic stress disorder (PTSD) (Madnick & Spokas, 2022), and eating disorders (Burnette et al., 2022). Finally, including diverse participants in RCTs without testing for moderating effects of specific demographic characteristics does not sufficiently address potential differences in intervention effects among demographic subgroups. For example, only 16% of RCTs conducted demographic subgroup analyses in studies of opioid use disorder interventions (Nalven et al., 2021) and only 9% of studies report moderation analyses based on participant demographic characteristics in PTSD RCTs, underscoring the pressing need to understand how multiple identities interact with efficacy (Madnick & Spokas, 2022). As clinical trials will build the evidence base and guide development of safe, effective PAT for real-world clinical populations, the critical time to ensure that research participants from diverse demographic backgrounds are represented is now.

There are specific reasons to consider the minoritized statuses of participants in PAT trials due to historical context, logistical challenges, and the specific disorders that PAT aims to treat. First, outcomes following psychedelic interventions depend on extra-pharmacological processes including participants’ prior beliefs and expectancies (Aday et al., 2022; Hartogsohn, 2016). Racism perpetuated by the War on Drugs (Williams et al., 2023), injustices committed against communities of color in early psychedelic research (Strauss et al., 2022), historical use of psychedelics for sexual orientation conversion therapy (Stauffer et al., 2022), and the fact that psychedelics remain criminalized (Ortiz et al., 2022) may affect the perspective of individuals from minoritized groups and therefore modulate clinical outcomes. Prior use of psychedelics, which varies with socioeconomic background and other demographic variables, may also influence outcomes (Krebs & Johansen, 2012; Viña & Stephens, 2023). Second, logistical barriers to participation in PAT trials may be more salient for certain minoritized groups. Because PAT trials can be particularly time- and resource-intensive due to the combination of psychotherapy and requirements for administering Schedule 1 substances, individuals from a low socioeconomic background may lack the financial and practical means to participate (Garcia-Romeu & Richards, 2018). Both literacy levels and participants’ immigration status may also yield language barriers, making enrollment and study procedures more difficult(Ortiz et al., 2022). Third, PTSD and depression have been a focus of PAT research thus far, and individuals from minoritized groups are at disproportionate risk for these diagnoses in part because of structural factors, systemic racism, and discrimination (Carter et al., 2023; Cole, 2009; Mongelli et al., 2020). As such, the diversification of research samples within PAT RCTs is critical to ensure the generalizability of the intervention to those at greatest risk of mental health disorders.

This systematic review focuses on the following demographic variables: gender, race, ethnicity, socioeconomic status, sexual orientation, and immigration status. The American Psychological Association’s Multicultural Guidelines identifies these variables as characteristics that are relevant to the treatment of mental health disorders (American Psychological Association, 2017), and these variables are commonly considered social determinants of health. The aims of this systematic review of PAT RCTs from 2017-2024 are to: 1) uncover the extent of reporting on participant demographic and cultural variables, and whether reporting practices have improved over time with implementation of federal guidelines and journal reporting standards; 2) determine the representativeness of specific demographic and cultural groups as compared to population and overall clinical trial estimates; 3) examine whether analyses of treatment effects based on participant demographic variables were conducted, and summarize key findings; and 4) explore differences in reporting and representation based on the psychedelic substance studied (MDMA or psilocybin).

2. Methods

2.1. Inclusion and Exclusion Criteria

We included studies that: (a) were published in a peer-reviewed journal, (b) utilized a RCT design (either parallel or crossover design acceptable), (c) administered psilocybin or MDMA for therapeutic purposes, (d) included a psychotherapeutic element along with the psychedelic substance, and (e) enrolled participants with diagnosed or clinical levels of ICD-10 (International Classification of Diseases, Tenth Edition), DSM-5 (Diagnostic and Statistical Manual of Mental Disorders), or DSM-4 psychiatric mental disorders (ascertained through clinical interviews or symptom scores above clinical threshold). We excluded dissertations, theses, conference abstracts, registered protocols without participant data, and unpublished preprints. We focus on RCTs only given that these studies are gold standard for evaluating which treatments are considered “evidence-based” (Djulbegovic & Guyatt, 2017). We also excluded trials that administered psychedelics other than psilocybin or MDMA or administered psilocybin or MDMA with no psychotherapeutic component. These compounds were chosen to reflect the growing body of scientific research supporting their therapeutic potential in combination with psychotherapy as well as their U.S. Food and Drug Administration (FDA) breakthrough therapy designation. We excluded publications that were follow-up or subsample studies from original published RCTs to prevent sample overlap.

2.2. Search Strategy

The protocol used to conduct this systematic review follows the Preferred Reporting Items for Systematic reviews and Meta-analyses (PRISMA) 2020 guidelines ((Page et al., 2021). We systematically searched the following electronic databases for relevant articles: PubMed, Embase, and PsycINFO. Search terms used Boolean operators to combine concepts related to psychedelic compounds (“psychedelic”, “hallucinogen*”, “3,4-Methylenedioxy methamphetamine”, “MDMA,” “psilocybin”), psychotherapy (“psychedelic-assisted psychotherapy”, “-assisted psychotherapy”, “psychotherapy”, “mental health”, “mental disorder*”) and RCT design (“randomized controlled trial”, “controlled trial”, “controlled”, “random*”). Search terms found in the title and/or abstract fields of citation records were used in combination with relevant controlled vocabulary from databases (e.g. MeSH terms from PubMed, PsycINFO Index terms, and Emtree terms from Embase). The search was conducted with a filter for articles published since January 1st, 1993, since studies conducted prior to the NIH Revitalization Act of 1993 do not meet current standards for methodological rigor or ethical practice guidelines (Johnson et al., 2008). “Back searching” was also conducted, whereby the bibliographies of relevant articles were searched to obtain additional articles. After search procedures, articles were imported into Covidence software where the two first authors proceeded with sequential stages of title/abstract screening, full-text screening, and data extraction. Authors conducted each stage independently, and resolved any discrepancies through discussion until consensus was reached. The initial search was conducted on 9/28/2023, with an updated search conducted on 5/5/2024. Figure 1 displays a PRISMA diagram of the search, screening, and selection process.

Figure 1.

Figure 1

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PRISMA Flow Diagram of Article Identification and Screening

2.3. Data Extraction and Synthesis

Using Covidence software (Veritas Health Organization, 2024), the first authors extracted the following information from included articles: first author name, year of publication, study country or countries, RCT study design, psychedelic substance used, placebo or control used, recruitment methods, sample diagnoses, sample size, ages of sample. In terms of main study demographic variables, the first authors coded whether the following sample variables were reported: gender, sexual orientation, race, ethnicity, socioeconomic status, and immigration status. If the variable was reported, the authors extracted the sample characteristics and sample size within that variable. Finally, the first authors coded whether any analyses were conducted incorporating these sociodemographic variables (e.g. as covariates, predictors, or moderators). Given the study aim to evaluate reporting in published articles, we did not contact study authors to obtain unreported or missing data. After finalization of data extraction, data were exported to R (Team, 2013) for computation of summary and frequency statistics as well as statistical tests of proportions. One proportion z-tests with Bonferroni-corrected significance levels were used to compare observed proportions of racial and ethnic participants in PAT RCTs to population estimates from census (United States Census Bureau, 2020) and clinical trial data (U.S. Food & Drug Administration, 2020).

2.4. Ethics, Transparency, and Openness

As this review was an assessment of published studies, review by an ethics board was not necessary. Before the study selection process, the study’s design protocol was preregistered on Open Science Framework, and associated materials are publicly available on this site: https://osf.io/js8q3/. The protocol was also registered on the international prospective register of systematic reviews (PROSPERO; https://www.crd.york.ac.uk/prospero/display_record.php?RecordID=468068).

3. Results

3.1. Study Characteristics

As detailed in the PRISMA flow diagram (Figure 1), our search strategy yielded a total of 1962 articles. After removal of duplicates and screening titles and abstracts for inclusion criteria, the co-first authors reviewed the full text versions of 59 articles. Ultimately, 21 of these articles, representing 1034 participants, met inclusion criteria and were included in the present review. Table 1 displays the study characteristics of included articles. Of these articles, 12 (57%) reported on trials involving psilocybin, while nine (43%) reported on trials involving MDMA. Most of the articles (62%) reported results from RCTs conducted solely in the United States, while the remaining involved trials conducted in Switzerland (9%), Canada (5%), UK (5%), Spain (5%), or multiple countries (14%). These published RCTs were designed to test the effects of PAT for a range of mental health conditions, including major depressive disorder (33%), PTSD (33%), cancer-related anxiety or depression (14%), alcohol use disorder (5%), life-threatening illness anxiety (5%), social anxiety disorder (5%), and obsessive compulsive disorder (5%).

Table 1.

Descriptive Characteristics of Studies Included in Review

MDMA-assisted Therapy Studies
First Author (Year of Publication) N Study Design Countries Diagnostic Groups Gender or Sex (F=Female, M=Male) Race and Ethnicity (% and Category As Reported) Socioeconomic Status Sexual Orientation Immigrant Status
Bouso (2008) 6 Parallel Group  Spain  PTSD 100% F NR Education – Degree
 (50% Grade School, 16.7% High School, 16.7% College)
Income
 (33.3% Low-Medium, 50% Medium, 16.7% Medium-High)
Employment Status
 (66.7% Unemployed, 16.7% Teacher, 16.7% Housewife)		 NR NR
Danforth (2018) 12 Parallel Group  USA  SAD 16.7% F
83.3% M		 50.0% White
16.7% Hispanic/Latino
8.3% Asian/Pacific Islander
8.3% Middle Eastern
8.3% Asian & Caucasian
8.3% Hispanic & Caucasian		 Employment Status
 (33.3% Full-time, 33.3% Unemployed, 16.7% Part-time, 16.7% Student)		 25.0% Non-heteronormative NR
Mitchell (2021) 90 Parallel Group  Canada; Israel, USA  PTSD 65.6% F
34.4% M		 76.7% White
8.9% Hispanic/Latinoa
8.9% Multiple
7.8% Asian
3.3% American Indian or Native Alaskan
2.2% Black/African American		 NR 96.0% Heterosexual NR
Mitchell (2023) 104 Parallel Group  USA; Israel  PTSD 71.1% F
28.9% M		 66.3% White
26.9% Hispanic/Latinoa
12.5% Multiple
10.6% Asian
7.7% Black/African American
1.9% American Indian/Alaska Native
1.0% Native Hawaiian/Pacific Islander		 NR NR NR
Mithoefer (2010) 20 Parallel Group  USA  PTSD 85.0% F
15.0% M		 100% Caucasian NR NR NR
Mithoefer (2018) 26 Parallel Group  USA  PTSD 27.0% F
73.0% M		 85% White
8% Latino/Hispanic
4% Native American
4% Native American & White		 NR NR NR
Oehen (2013) 12 Parallel Group  Switzerland  PTSD 83.3% F
16.7% M		 NR Employment Status
 (42% On disability, 25% Limited employment, 25% Full-time, 8% Retired)		 NR 8.3% Foreign Born
Ot’alora (2018) 28 Parallel Group  USA  PTSD 67.9% F
32.1% M		 92.9% White
3.6% Latino/Hispanic
3.6% Native American		 NR NR NR
Wolfson (2020) 18 Parallel Group  USA  Life threatening illness anxiety 77.8% F
22.2% M		 83.3% White
5.6% Black/African American
5.6% White/Native American
5.6% “Other”		 NR NR NR
Psilocybin-assisted Therapy Studies
First Author (Year of Publication) N Study Design Countries Diagnostic Groups Gender or Sex (F=Female, M=Male) Race and Ethnicity (% and Category As Reported) Socioeconomic Status Sexual Orientation Immigrant Status
Bogenschutz (2022) 95 Parallel Group  USA  AUD 44.2% F
55.8% M		 78.9% White
14.7% Hispanica
4.2% Black
3.2% Asian
1.1% American Indian/Alaska Native		 Income
 (Range: $3700-$4,000,000, Median: $100,000)		 NR NR
Carhart-Harris (2021) 59 Parallel Group; Within-Subjects  UK  MDD 33.9% F
66.1% M		 88.1% White Education – Years
( 76.3% University)
Employment Status
 (71.2% Employed, 20.3% Unemployed, 8.5% Student)		 NR NR
Davis (2021) 24 Parallel Group; Within-Subjects  USA  MDD 66.7% F
33.3% M		 91.7% White Education – Degree
 (58% Bachelor’s, 17% Master’s, 8% Advanced, 8% Associate’s, 8% < College)
Employment Status
 (63% Full-time, 21% Unemployed, 17% Part-time)		 NR NR
Goodwin (2022) 233 Parallel Group  Canada; Czech Republic; Denmark  MDD 51.9% F
48.1% M		 92.3% White NR NR NR
Griffiths (2016) 51 Crossover  USA  Cancer-related anxiety and depression 49.0% F
51.0% M		 94% White
4% Black/African American
4% Asian		 Education – Degree
 (53% Post-graduate, 45% College, 2% High school)		 NR NR
Grob (2010) 12 Within-Subjects  USA  Cancer-related anxiety 91.7% F
3.8% M		 NR NR NR NR
Moreno (2006) 9 Within-Subjects  USA  OCD 22.2% F
77.8% M		 NR Employment Status
 (55.6% Unable to work, 33.3% Employed, 11.1% Housewife)		 NR NR
Raison (2023) 104 Parallel Group  USA  MDD 50.0% F
50.0% M		 89.4% White
15.4% Hispanic/Latinoa
5.8% Multiracial
2.9% Black/African American		 Income – Annual
 (40.4% >$100k, 13.5% $75k-$99.9k, 7.7% $50k-$74.9k, 10.6% $25k-49.9k, 13.5% <$24.9k)		 NR NR
Rosenblat (2024) 31 Crossover  Canada  MDD 38.7% F
61.3% M		 NR NR NR NR
Ross (2016) 29 Parallel Group;
Crossover		  USA  Cancer-related anxiety and depression 62.0% F
38.0% M		 90% White
10% “Other”		 Education – Degree
 (48% Graduate school, 31% 4-year college, 14% Part college, 3% High school, 3% Grade 7-12)
Employment Status
 (41% Full-time, 21% Retired, 14% Part-time, 7% Self-employed, 7% Unemployed, 7% Long-term disability, 3% Student)		 NR NR
Sloshower (2023) 19 Within-Subjects  USA  MDD 68.4% F
31.6% M		 84.2% White
10.5% Black
10.5% Hispanica
5.2% Two or More Races		 Education – Degree
 (57.8% College, 26.3% Masters, 10.5% High school, 5.2% Some college)
Employment Status
 (47.8% Part-time, 36.8% Full-time, 15.7% Unemployed)		 NR NR
von Rotz (2022) 52 Parallel Group  Switzerland  MDD 63.5% F
36.5% M		 94.2% White
3.8% Arab
1.9% Black Caribbean		 Education – Years
 (Mean: 14.7)		 NR NR
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Note.

N=Participant sample size; NR = Not reported; AUD = Alcohol Use Disorder; PTSD = Posttraumatic Stress Disorder; SAD = Social Anxiety Disorder; MDD = Major Depressive Disorder.

a

Indicates that Hispanic or Latino ethnicity were collected separately from racial categories, so percentages add up to more than 100%.

3.2. Reporting of Sociodemographic Characteristics in PAT Trials

Figure 2 displays the percentage of studies reporting on each participant sociodemographic characteristic, and Table 1 displays which studies reported on individual characteristics.

Figure 2.

Figure 2

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Number and Percentage of Psychedelic-assisted Psychoherapy RCTs Reporting Participant Sociodemographic Characteristics

3.2.1. Gender

All studies reported participant gender. No study clarified how participant gender was collected in terms of wording to participants or mentioned collection of gender identity. Therefore, it is unclear whether this variable represents participant biological sex-at-birth or gender identity across studies.

3.2.2. Race or Ethnicity

Of the included studies, 16 (76%) reported either participant race or ethnicity. Five of these studies included categories that reported race as “Other” or “Non-White”. Three studies reported race and ethnicity together by including ethnic background (Hispanic or Latino origin) as a racial category. Five studies reported participants’ race and ethnicity separately. The remaining eight studies that reported participant racial backgrounds did not enroll Hispanic or Latino participants, so separate reporting of ethnicity cannot be evaluated.

3.2.3. Socioeconomic Status

12 studies (57%) reported participant SES, with five reporting multiple metrics of SES. Of the 12 that reported SES, eight reported employment status, seven education (five reported degree attainment, two reported total years of education), two numerical income, and one categorical income (low, middle, high).

3.2.4. Sexual Orientation

Two (9.5%) studies reported participants’ sexual orientation, with both reporting this as the percentage of participants who identified with a heterosexual or heteronormative sexual orientation.

3.2.5. Immigration Status

One (4.8%) study reported participants’ immigrant background by reporting participants’ aggregated countries of origin.

3.2.6. Time Trends

The included articles were published between the years of 2006 and 2024. We examined reporting on race and ethnicity in the time since ClinicalTrials.gov began requiring reporting of race and ethnicity information during results submission in April 2017. Of the seven articles published before this requirement, only three (42.9%) reported race or ethnicity. Of the 13 articles published after this requirement, 12 (92.3%) reported race or ethnicity. The proportion of participants with an unreported race or ethnicity significantly decreased from the decade 2010-2019 (12.6%) to the decade 2020-2024 (1.8%; χ2(1)=46.29, p<.001). Of the 12 studies that reported SES, half (50%) were published in the last five years, and nine (75%) were published in the last 10 years. Both articles reporting participant sexual orientation were published in the last five years, and the article reporting immigration status was published in the last 10 years.

3.3. Representation of Sociodemographic Groups in Psychedelic-assisted Psychotherapy Trials

3.3.1. Gender

Across studies and the total sample of 1034 participants, women comprised 55.4% of all RCT participants, and men comprised 44.6% of RCT participants. Almost all studies enrolled both male and female participants, except for one study that enrolled only female participants. No studies reported enrollment of nonbinary or transgender individuals.

3.3.2. Race or Ethnicity

None of the RCTs focused on a racial or ethnic minoritized group. Figure 3 shows the racial and ethnic representation of participants from PAT RCTs conducted in the U.S. (N=447) compared to both racial and ethnic representation of the U.S. population from 2020 U.S. Census data (United States Census Bureau, 2020), as well as to U.S. clinical psychiatric drug trial representation conducted from 2015-2019 (Lolic et al., 2021). Participants from studies that did not report race or ethnicity were labeled as a “Not Reported” racial category. White participants represented the majority of U.S. PAT RCT samples (82.1%), which is a significantly higher proportion than White participants in U.S. psychiatric clinical drug trials from 2015-2019 (51.1%, p<.001), and is also significantly higher than is reflected by U.S. Census 2020 data (57.8% White, p<.001).

Figure 3. Racial and Ethnic Demographic Data from U.S. Psychedelic-assisted Psychotherapy Trial Participants Compared to U.S. Census and U.S. Psychiatric Clinical Drug Trial Summary Data.

Figure 3

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Note. Participants from studies that did not report race or ethnicity were labeled as a “Not Reported” category. The “Unspecified” category includes individuals described as “Non-White” or “Other” in U.S. Psychedelic Therapy RCTs, includes individuals described as “Some other race” in U.S. Census Data 2020, and includes individuals aggregated into a single category who identified as “Mixed Race”, “Native Hawaiian,” “Unknown”, or “Other Race” in U.S. Clinical Trials 2015-2019.

In three studies, race and ethnicity were reported separately. Therefore, the sum of proportions is greater than 100% due to multiple categories selected by participants in these studies.

***=statistically significant difference according to the Bonferroni-corrected p-value of .00025 in a one-proportion Z-test.

The proportion of Asian American participants in U.S. PAT RCTs (1.1%) did not significantly differ from U.S. psychiatric drug trials (1.2%) but was significantly lower than U.S. Census data (5.9% Asian, p<.001). The proportion of Hispanic or Latino participants in U.S. PAT RCTs (8.5%) did not significantly differ from U.S. psychiatric drug trials (11.3%) but was significantly lower than representation in U.S. Census data (18.7%, p<.001). The proportion of Black participants in U.S. PAT RCTs (2.7%) was significantly lower than that of both U.S. psychiatric drug trials (45%, p<.001) and U.S. Census data (12.1%, p<.001). The proportions of multiracial (2.5%), American Indian/Alaska Native (0.7%), Hawaiian/Other Pacific Islander (0.0%), and Unspecified (1.3%) participants were not significantly different from U.S. census data – because the FDA aggregates these racial categories, comparisons of these groups to U.S. psychiatric drug trials cannot be made.

Figure 4 displays the racial and ethnic representation of participants from all PAT RCTs globally compared to racial and ethnic representation of global clinical trials conducted from 2015-2019 for all therapeutic areas (U.S. Food & Drug Administration, 2020). White participants represented the majority of PAT RCT samples (79.8%), which was significantly higher than the proportion of White participants from global clinical trials from 2015-2019 (76%, p=.004). Several racial and ethnic minoritized groups were underrepresented in PAT RCTs compared to global clinical trials from 2015-2019, including those identifying as Hispanic or Latino (7.2% vs. 13%, p<.001), Black/African American (2.2% vs. 7%, p<.001), and Asian or Asian American (2.2% vs. 11%, p<.001). The proportions of multiracial (2.0%), American Indian/Alaska Native (0.6%), Hawaiian/Other Pacific Islander (0.0%), and Unspecified (3.3%) participants could not be compared to global clinical trials due to a lack of disaggregated clinical trial data.

Figure 4. Racial and Ethnic Demographic Data from Psychedelic-assisted Psychoherapy Trial Participants Compared to Global Clinical Trial Summary Data.

Figure 4

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Note. The “Unspecified” category includes individuals described as “Non-White” or “Other” in U.S. Psychedelic Therapy RCTs, and includes individuals aggregated into a single category who identified as “Mixed Race”, “Native Hawaiian,” “Unknown”, or “Other Race” in Global Clinical Trials 2015-2019.

Global clinical trial data (N=292,537) represents all therapeutic areas, since racial and ethnic data for psychiatry specifically was unavailable.

In three studies, race and ethnicity were reported separately. Therefore, the sum of proportions is greater than 100% due to multiple categories selected by participants in these studies.

*=statistically significant difference according to the Bonferroni-corrected p-value of .0125 in a one-proportion Z-test.

***=statistically significant difference according to the Bonferroni-corrected p-value of .00025 in a one-proportion Z-test.

3.3.3. Socioeconomic Status

Of the eight studies (n=168 participants) that reported employment status (62.5% U.S. studies), 64.3% of participants were employed (full- or part-time), 26.8% were unemployed, 4.8% were students, and 4.2% were retired. For only those studies conducted in the U.S. (n=150 participants), 69.3% of participants were employed (full- or part-time), 19.0% were unemployed, 4.8% were students, and 3.6% were retired. The employment rate across U.S. study participants (69.3%) is comparable to the average employment rate in the U.S. from the years 2006 to 2023 (59.8%; (Statista Research Department, 2024). Of the five studies (including 129 participants) that reported educational attainment (80% U.S. studies), 3.9% of participants did not complete high school or equivalent, 3.9% completed high school, 5.4% completed some college, 46.5% completed college (associate or bachelor’s degree), and 40.3% completed an advanced degree such as a master’s degree or doctoral degree. For only those studies conducted in the U.S. (n=123 participants), 0.8% of participants did not complete high school or equivalent, 3.1% completed high school, 5.4% completed some college, 45.7% completed college (associate or bachelor’s degree), and 40.3% completed an advanced degree such as a master’s degree or doctoral degree. The proportion of U.S. participants from PAT RCT studies with a college degree (45.7%) is significantly higher than the U.S. population age 25 or older with a college degree (23.5%; p<.001; United States Census Bureau, 2022). Similarly, the proportion of participants with an advanced degree (40.3%) is significantly higher when compared to the proportion of the U.S. population with an advanced degree (14.4%; p<.001). Due to a low proportion of PAT RCTs reporting participant income, participant representativeness in these domains cannot be evaluated.

3.3.4. Sexual Orientation

Of the two studies reporting participant sexual orientation (n=36), 83.3% of participants reported identification as heterosexual. One study was conducted in the U.S. and the other was conducted in the U.S., Canada, and Israel. According to U.S. Census Bureau estimates, 88.3% of the population identifies as heterosexual or straight (Anderson et al., 2021).

3.3.5. Immigrant Background

Since only one study reported participant immigrant background, representativeness in this domain could not be evaluated.

3.3.6. Time Trends

Time trends for SES, sexual orientation, immigration status could not be evaluated due to infrequent reporting and heterogeneity. Overall, the sample makeup of PAT RCTs did not change substantially over time for sex/gender. In terms of race and ethnicity, the proportion of Hispanic or Latino participants significantly increased from the decade 2010-2019 (3.2%) to 2020-2024 (8.2%; χ2(1)=5.11, p=.024). There were no other statistically significant changes in other racial and ethnic categories.

3.3.7. Psychedelic Substance (MDMA vs. Psilocybin)

Overall, 316 participants came from MDMA-assisted therapy RCTs and 718 participants came from psilocybin-assisted therapy RCTs. There was a significant association between participant sex and psychedelic substance, with MDMA studies having a greater proportion of female participants (65.8%) compared to psilocybin studies (50.8%; χ2(1)=19.35, p<.001). MDMA studies were more racially diverse than psilocybin studies, enrolling a significantly greater proportion of participants who were American Indian/Alaska Native (2.2% vs. 0.1%, p=.001), Asian/Asian American (6.0% vs. 0.6%, p<.001), multiracial (7.9% vs. 1.0%; p<.001), Hispanic/Latino (13.3% vs. 4.5%; p<.001), and fewer participants who were White (71.8% vs. 83.2%; p<.001). The proportion of Black participants was not significantly different between MDMA studies (3.5%) and psilocybin studies (1.7%). Due to limited reporting, MDMA and psilocybin RCTs could not be meaningfully compared on SES, sexual orientation, or immigrant background.

3.4. Moderating Effects Across Sociodemographic Subgroups

Four studies conducted analyses to examine the influence of sociodemographic variable factored on treatment outcome, with all four specifically investigating the role of sex/gender. One study conducted between-group comparisons with gender and reported that gender did not influence primary outcome measures (Ross et al., 2016). Another study included gender as a covariate in exploratory analyses and found that gender did not interact with the treatment to influence primary endpoints (Mitchell et al., 2021). However, a separate study found that female sex assigned at birth was associated with improved outcomes in PTSD symptom reduction for both MDMA-assisted therapy and placebo groups (Mitchell et al., 2023). A fourth study controlled for sex in their main analyses of treatment effects (Raison et al., 2023), but did not report whether sex was a significant covariate.

4. Discussion

This systematic review identified limitations in reporting, representation, and analysis of moderating effects of participant sociodemographic characteristics in PAT RCTs. First, demographic characteristics like sexual orientation and socioeconomic status are infrequently reported in PAT RCTs. Second, there is marked overrepresentation of White participants and significant underrepresentation of Black participants in these trials. Third the limited data reported with respect to participants’ educational attainment suggest that PAT RCT samples are disproportionately comprised of socioeconomically advantaged individuals. Finally, analyses of moderating effects based on participant sociodemographic characteristics are virtually nonexistent. Consequently, it remains unclear whether PAT effectively serves the diverse population it is designed to treat. To improve the generalizability of PAT interventions, our results highlight the urgent need for clinical trials to systematically report sociodemographic characteristics and to expand the diversity of trial samples.

The first step in evaluating the extent to which PAT is effective for diverse participants is measuring and reporting relevant participant characteristics. Our results showed that similar to RCTs of other mental health treatments (Burnette et al., 2022; Harned et al., 2022; Polo et al., 2019), gender was consistently reported across all studies. However, no RCTs reported non-cisgender identities, suggesting that sex and gender identity may be conflated in these studies. Only two RCTs of the 20 examined reported sexual orientation. As sexual and gender minority groups are at heightened risk of suicide and other mental health disorders (Horwitz et al., 2020; Lund & Burgess, 2021; Ramchand et al., 2022), failure to report these variables, at minimum, means the impact of this intervention on sexual and gender minority groups remains unknown. Although some researchers may fear that participants will find these questions too private to answer, research shows that participants are willing to provide this information when asked in a culturally sensitive manner (Ellis et al., 2017). The American Psychiatric Association, American Psychological Association, FDA, and National Institutes of Health all call for reporting of these demographic characteristics as a necessary first step to developing evidence-based mental health treatments for sexual and gender minority groups (American Psychological Association, 2021; Cabaj, 2024; National Academies of Sciences and Medicine, 2022; U.S. Food & Drug Administration, 2024).

While most of the included studies reported either participant race or ethnicity, some RCTs published in the past year still do not report these variables. Our study revealed additional challenges with respect to reporting racial and ethnic data. For example, several studies reported race as “Other” or “Non-White,” which is both uninformative and problematic with continued centering of a White racial category (Flanagin et al., 2021). Additionally, heterogeneous reporting of race and ethnicity, or conflating the two, obscures the identification of trends in inclusion of various racial and ethnic groups across studies and time. This heterogeneity is not unique to PAT RCTs – nomenclature on racial and ethnic categories has continued to evolve, with reporting standards and U.S. census categories shifting over time (Viano & Baker, 2020). Current federal guidelines in the U.S. recommend using a single combined race and ethnicity question that allows participants to select one or multiple categories (Office of Management and Budget, 2024).

In terms of representation, PAT RCTs were generally gender balanced for women and men, while omitting reporting on other gender identities. Participants from the U.S. with higher levels of educational attainment were overrepresented in PAT RCTs compared to U.S. population data on educational attainment, although this is based on the limited number of studies that measured and reported socioeconomic status via educational attainment. Nonetheless, this finding suggests that PAT RCTs may be less accessible to individuals from lower SES groups. Participants from more educated backgrounds may have increased familiarity with and trust in academic medical institutions. Logistical considerations related to low SES (e.g. transportation barriers, childcare, hourly work schedules) may also render participation in PAT RCTs particularly difficult, because these trials may involve several inflexible, day-long commitments over the course of weeks to months with low pay. Therefore, targeted efforts to recruit participants from low SES groups may be necessary to increase SES-related representation in PAT RCTs. At minimum, accessible transportation options, increased compensation for participation, and maximal flexibility in scheduling study visits are concrete steps to ensure fair access for all SES groups to clinical trials. Compensation in the form of cash or gift cards rather than checks may be especially beneficial, as this will facilitate participation for individuals without bank accounts (Williams et al., 2020).

Regarding racial-ethnic representation, White participants vastly outnumbered other racial groups (79.8%), particularly Black and Hispanic or Latino-identifying participants. This finding mirrors that of a prior review of 18 PAT studies (including non RCTs) from 1993 to 2017, which found that 82.3% of participants identified as White (Michaels et al., 2018b), as well as a recent systematic review evaluating ethnoracial diversity in psychedelic studies since 2018 (Hughes & Garcia-Romeu, 2024). The lack of Black participants enrolled in PAT RCTs (2.2%) is particularly egregious in comparison to population data and summary data from RCTs of other psychiatric interventions, such as those for self-injurious thoughts and behaviors (21.4% Black; Maria Guzmán et al., 2024), PTSD (20.4% Black; Madnick & Spokas, 2022), depression (10.1% Black; Polo et al., 2019), anxiety (6.9% Black; Ong et al., 2024), and 2015-2019 FDA clinical trials for psychiatric disorders (45% Black; Lolic et al., 2021).

Recruitment of racial and ethnic minoritized groups may be particularly challenging for PAT trials for several reasons, including the prevailing image of the psychedelic community as “whitewashed,” the feelings of vulnerability and powerlessness associated with high dosages of psychedelic drugs, and intersection with low SES. Several other possible reasons for lack of diversity in psychedelic science are summarized in detail elsewhere (see Ortiz et al., 2022). To address the lack of balanced racial and ethnic representation in PAT RCTs, building trust with minoritized groups from recruitment and onwards is essential. By engaging voices from target demographic groups early in the research process, even before clinical trial design, investigators can better address barriers to enrollment and promote equitable access to the intervention. Methods to build trust in PAT trials with communities of color may include community talks by study therapists, creation of research fliers that include the names and pictures of study staff, as well as use of language about the site’s culturally sensitive and respectful treatment approach (Williams et al., 2020).. In a separate study, after receiving brief psychoeducation related to MDMA and PAT, Black American participants endorsed more interest and positivity towards PAT compared to White American participants (Carter et al., 2023). These studies suggest that active outreach efforts that include accessible information about the research study and PAT broadly can rebuild trust among communities and researchers with the goal to increase diversity in PAT RCT samples.

Our review found that clinical trials of MDMA have higher female representation and greater racial diversity compared to clinical trials involving psilocybin. This may reflect a 2020 initiative by the sponsor of MDMA clinical trials designed to increase ethnoracial diversity among participants of Phase 3 clinical studies of MDMA-assisted therapy for PTSD, which successfully increased enrollment of non-White participants (McKenna Leighton & Charlotte Harrison, 2022; Mitchell et al., 2023). The specific strategies of this initiative included ample financial compensation for participants and reimbursement of study-related costs. Efforts also included increasing the demographic diversity of the clinical staff on the study, which is shown to reduce medical distrust among communities of color (Bazargan et al., 2021). As most clinical trials of MDMA have focused on PTSD treatment, a higher representation of women likely reflects that women are twice as likely to suffer from PTSD compared to men, observed both in the U.S. and internationally (Kimerling et al., 2018; Maney, 2016). The modern scientific study of PAT has been limited to only a few indications; thus, it is too soon to draw conclusions about the differences in sociodemographic diversity between these two substances. Rather, a concerted effort to ensure diversity in all trials of PAT will help to elucidate for whom a specific drug and intervention are best suited.

4.1. Strengths and Limitations

Results of this systematic review should be considered in the context of several limitations. First, our search strategy was limited to RCTs, as these studies are the backbone of widely disseminated evidence-based treatments. Open-label and retrospective studies may display different trends in reporting and representation of sociodemographic variables. Second, investigators were not contacted for missing participant sociodemographic information. This choice was intentional, as the study aimed to understand reporting practices in scientific dissemination. Demographic data may have been collected in these trials, though not reported. Third, as the majority of included studies were conducted in the U.S., most population comparisons are based on U.S. data. We selected U.S. data for comparison given that comprehensive global data on many variables is not available, and because of our goal to inform the U.S. context where both psilocybin and MDMA have been given breakthrough status by the FDA. Consequently, the conclusions drawn from this study are most generalizable to U.S. based research. With growing numbers of international trials, future reviews should compare regional representation.

4.2. Conclusion

This study provides an updated systematic review of sociodemographic reporting and representation in PAT RCTs. This systematic review revealed ongoing gaps in reporting and disparities in representation of participant sociodemographic characteristics in modern PAT RCTs. Studies rarely consider the moderating influence of participant sociodemographic backgrounds. To draw conclusions about the generalizability of PAT, reporting, inclusion, and statistical practices must improve to ensure that emerging data are applicable to minoritized groups who are disproportionally affected by moderate to severe mental health concerns. Community participatory research can inform equitable access to RCTs of PAT through intentional recruitment efforts and enhanced clinical trial design, while building needed trust with minoritized communities. Such efforts are an essential part of generating robust evidence for PAT and ultimately delivering safe and effective treatments that reduce mental health disparities.

Table 2.

Overall Participant Sex/Gender and Race and Ethnicity Across Psychedelic Therapy RCTs by Decade

Overall
(k=21, n=104)		 2006-2009
(k=2, n=15)		 2010-2019
(k=8, n=190)		 2020-2024
(k=11, n=829)
Sex/Gender (%)
Female 55.4 53.3 57.4 55.0
Male 44.6 46.7 42.6 45.0
Race and Ethnicity (%)
White 79.8 - 77.9 81.7
Hispanic or Latino 7.2 - 3.2* 8.2*
Black or African American 2.2 - 1.1 2.5
Asian/Asian American 2.2 - 1.1 2.5
American Indian/Alaska Native 0.8 - 1.1 0.7
Hawaiian/Other Pacific Islander 0.1 - 0.0 0.1
Multiracial 3.1 - 1.6 3.5
Unspecified 3.0 - 1.6 3.4
Not Reported 6.8 100.0 12.6*** 1.8***
Open in a new tab
*

p<.05,

***

p<.001 according to a two proportions Z-test comparing 2010-2019 to 2020-2024.

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