Ethnoracial inclusion in clinical trials of psychedelics: a systematic review

Background Prior data indicate limited ethnoracial diversity in studies testing psychedelic-assisted treatments. Regulatory approval for psychedelic treatments may be imminent given growing evidence for safety and ef fi cacy in a variety of psychiatric conditions. Data on racial and ethnic inclusion rates in clinical psychedelic studies since 2018 have not been systematically reported to date. With the publication of multiple new studies in the fi eld, an update to existing ethnoracial inclusion data is needed to inform the state of the science and future directions for research. Methods Systematic review of Pubmed/MEDLINE, EMBASE, and Web of Science for studies of any design testing a psychedelic treatment for a psychiatric or substance use disorder published between January 1, 1994 and May 24, 2024. Search terms related to serotonergic psychedelics and MDMA, psychedelic therapies, psychiatric disorders, and substance use disorders were used. References of reviewed studies were screened for inclusion. Studies were rated for quality on a fi ve-point scale ranging from 1 (most rigorous, i.e., properly powered randomized clinical trial) to 5 (least rigorous, e.g., case reports). Separate analyses were performed for two groups of studies, one involving all included studies meeting search criteria, and the other involving only studies from the USA. Rates of inclusion of different ethnoracial groups were calculated between studies published before and after December 31, 2017. Additionally, the proportion of White vs. non-White participants was compared between studies published before and after December 31, 2017. Finally, a nonparametric Mann - Whitney U test was used to compare the relative quality ratings of studies published before and after December 31, 2017. Findings 787 studies were screened, and 39 studies were included. This included 16 studies (n = 282) from a prior review published in 2018 with an additional 23 studies (n = 1111) that were published after 2017, consisting of 14 randomized controlled studies, 8 open-label studies, and 1 placebo-controlled, within-subject, fi xed-order study. In all included studies published after 2017, 85.6% of participants identi fi ed as non-Hispanic White, 3.1% as Black, 6.8% as Latinx/Hispanic, 3.6% as Asian, 1.2% as Indigenous, 3.5% as mixed race, 1.4% as other, Pooled data from all included studies (n = 1393) found 85.0% of participants identi fi ed as non-Hispanic White, 2.9% as Black, 5.9% as Latinx/Hispanic, 3.2% as Asian, 1.9% as Indigenous, 3.7% as mixed race, 1.4% as other. In studies conducted in the USA (n = 1074), 908 (84.5%) of participants identi fi ed as White, 36 (3.4%) as Black, 80 (7.4%) as Latinx/ Hispanic, 43 (4.0%) as Asian, 15 (1.4%) as Indigenous, 40 (3.7%) as Mixed, and 9 (0.8%) as Other. Differences in inclusion rates were found when comparing studies published before and after December 31, 2017 for all included studies and all studies conducted in the USA. The proportion of White to non-White participants was found to have decreased in studies conducted in the USA over the same period, but not for all included studies. Interpretation Underrepresentation of ethnoracial minoritized populations persists in studies examining psychedelic therapies, despite growing calls for diversity. Non-Hispanic White participants remain an over-represented majority by a large margin, though, there were greater proportions of ethnic minoritized populations included in studies since 2018, particularly in studies conducted in the USA. This indicates progress towards equity in psychedelic research, though much work is needed to inform the safety and ef fi cacy of psychedelic treatments in the general population. Funding There was no funding source for this study. Copyright (c) 2024 The Author(s). Published by Elsevier Ltd. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).