Unequal representation? A cross-sectional analysis of age, sex, race, and ethnicity in clinical trials of classic psychedelics.

Background: Although classic psychedelic trials show therapeutic potential, the limited diversity of participants raises concerns about generalizability and safety.

Aims: This study assesses the representation of race, ethnicity, and sex in interventional clinical trials of psilocybin and lysergic acid diethylamide (LSD) to evaluate disparities in participant diversity.

Methods: We conducted a cross-sectional analysis of interventional trials registered on ClinicalTrials.gov up to 12 January 2025 that focused on classic psychedelics (psilocybin, psilocin, LSD, DMT, 5-MeO-DMT, and mescaline). Eligible trials were phases 2-4 and targeted psychiatric disorders or symptoms. Trials involving only healthy participants were excluded. Two reviewers extracted trial-level data independently; discrepancies were resolved by consensus.

Results: Nine eligible trials included eight with psilocybin and one with LSD. In the psilocybin trials (n = 501), the age of participants ranged from 34.3 to 56.3 years; 47.7% were women. White participants accounted for 87.2%, while Black participants accounted for 3.0%, and Asian individuals accounted for 5.0%. Ethnicity was reported in 4 of 8 psilocybin trials (n = 134), with 13.4% identifying as Hispanic or Latino. In four U.S.-only trials(n = 139), participation-to-population ratios (PPRs) confirmed the underrepresentation of Black (PPR = 0.317) and Asian participants (PPR = 0.799). The LSD trial (n = 11) included older adults (average age: 51.7 years) who did not provide any information on race or origin.

Conclusions: The limited diversity in psychedelic trials demonstrates the need for broader recruitment. Without better representation, the safety and efficacy of these therapies remain uncertain. Standardized reporting and targeted strategies are essential to ensure equity.