Study Warns Drug Trials are Lacking Diversity
A new analysis from University of California (UC) Riverside and UC Irvine researchers finds that the vast majority of pivotal clinical trials used to secure FDA drug approvals fail to reflect the racial and ethnic makeup of the U.S., and that representation has worsened in recent years. Published in Communications Medicine, the study reviewed 341 pivotal trials conducted between 2017 and 2023. Only 6% of those studies included participant demographics that matched U.S. population distributions, the authors report, with black and Hispanic enrollment declining steadily beginning in 2021. Meanwhile, Asian representation increased and white enrollment remained largely stable. The findings come as federal agencies, drug developers, and health equity advocates are pushing for more representative research to support the growth of precision medicine.
“Precision medicine relies on understanding how genetic differences influence treatment outcomes,” said co-lead author Sophie Zaaijer, a geneticist affiliated with UC Riverside and UC Irvine. “If clinical trials under-sample large segments of human genetic variation, critical signals for safety and efficacy may be missed.”
Her co-author, UC Riverside geneticist Simon “Niels” Groen, warned that limited ancestry representation undermines confidence in the generalizability of findings. “When a trial includes only a narrow slice of humanity, we can’t be confident a drug will work — or be safe — for everyone it’s meant to help,” he said.
While U.S. approvals rely heavily on multinational trials conducted under International Council for Harmonization (ICH) standards, the research team notes that these studies are disproportionately performed in the U.S., Europe, China, and Japan. Sub-Saharan Africa and much of Latin America account for less than 3% of pivotal trials, leaving large genetic and environmental backgrounds unrepresented despite their relevance to drug metabolism.
The authors suggest this imbalance could shift as more Latin American countries integrate into the ICH system. Brazil joined in 2016, Mexico in 2021, and Argentina in 2024 — moves that may open new sites for studies aiming to capture broader genetic diversity.
The study authors call for drug developers and regulators to set diversity objectives at the earliest stages of development, expand trial geographies to match the health and genetic profiles of patient populations, and routinely collect biological samples to better understand drug response variability.
As precision medicine continues to advance, the authors argue that the field’s promise will remain limited without more representative data. “Precision medicine becomes possible only when clinical trials map the biology of all patients, not just a subset,” Groen said. “Our analysis could offer a roadmap for how to get there.”