By Brandon Lim
December 20, 2025 · 3 min read[Photo credit to Unsplash]
Just 6% of 341 trials behind US drug approvals from 2017 to 2023 matched the country's racial makeup, a UC Riverside study released December 12, 2025 found, days before the FDA issued new trial rules.
The gap matters because a drug tested mostly on one group can hide side effects or weaker results in patients whose genes differ, the researchers warned.
Geneticists Sophie Zaaijer and Simon Groen published the analysis in Communications Medicine on December 5, 2025, after reviewing every pivotal trial that supported an FDA approval over seven years.
Pivotal trials refer to the large late-stage studies that decide whether a drug reaches pharmacy shelves.
The team checked whether each trial enrolled enough White, Black, Hispanic, and Asian participants to reflect US census figures, and most trials fell short on at least two groups.
Representation of Black participants peaked in 2019 and then slid, so that only 23% of the 2023 trials hit the mark.
Hispanic participants fared little better, with just 30% of 2023 trials enrolling enough of them.
Geography explains much of the split, according to the authors.
Asian participants moved the other way, reaching proper representation in 81% of 2023 trials as drug makers shifted more of their testing overseas.
The share of trial sites inside the United States fell from 47% in 2020 to 25% in 2023.
Trials that kept every site on US soil enrolled an average of 17.7% Black participants, while trials spread across Europe, China, and Japan drew mostly White and Asian volunteers.
Sub-Saharan Africa and Latin America, home to large Black and Hispanic populations, hosted less than 3% of the trials.
Cancer trials showed the widest gap, enrolling an average of 4% Black participants even though Black Americans carry a heavier cancer burden than other groups.
Zaaijer put the danger plainly in the university's announcement: "If clinical trials under-sample large segments of human genetic variation, critical signals for safety and efficacy may be missed."
The FDA answered part of that concern on December 15, 2025, when it published a final guidance titled "Enhancing Participation in Clinical Trials."
The document asks drug makers to stop automatically excluding older adults, people with several illnesses, and patients at the extremes of body weight.
It also urges sponsors to cut the number of clinic visits, allow electronic consent, send health workers to patients' homes, and recruit at community venues.
One word vanished, however: the 2020 version carried "diversity" in its title, and the 2025 version does not.
Law firm King & Spalding noted on December 19, 2025, that the new text still names race, ethnicity, sex, and age as enrollment factors but never uses the term diversity.
The shift follows a January 2025 executive order from President Donald Trump that curtailed federal diversity, equity, and inclusion programs.
Within days of that order, the FDA pulled a June 2024 draft guidance on Diversity Action Plans from its website, AJMC reported on January 31, 2025.
Congress had required those plans in a December 2022 law, which tells sponsors to set enrollment goals by race, ethnicity, sex, and age before starting most late-stage trials.
The Riverside study found that 91 sponsors had already filed such plans voluntarily in 2020 and 2021, and the authors argued that the plans should become mandatory rather than optional.
None of the sources report how the FDA intends to enforce the 2022 requirement under the new guidance.
The authors also pushed for adding countries with large Black and Hispanic populations to the International Council for Harmonisation, the body whose standards decide where drug companies feel safe running trials.
Until that happens, Zaaijer and Groen wrote, the global map of trial sites will keep tilting toward White and Asian populations.
The study leaves one question on the table: what should "representative" mean when a drug gets sold to everyone but tested on a few?
