Study Reveals Clinical Trials Fail to Reflect U.S. Diversity

A recent study highlights a significant gap in the representation of racial and ethnic diversity in U.S. clinical trials for new drugs. Researchers from the University of California Riverside (UCR) and the University of California Irvine (UCI) found that only 6% of pivotal trials between 2017 and 2023 adequately reflected the nation’s demographic makeup. The analysis indicates a troubling trend, with decreasing participation rates for Black and Hispanic individuals even as calls for greater equity in medical research have intensified.

The study scrutinized data from 341 pivotal trials—those crucial studies that contribute to securing FDA approval for new medications. Notably, while enrollment of Black and Hispanic participants declined, Asian representation increased, and white participation remained stable. This disparity raises concerns about the efficacy and safety of treatments designed for a diverse population, emphasizing the need for more inclusive research practices.

Understanding genetic diversity is critical in precision medicine, which aims to tailor treatments to individual genetic profiles. Sophie Zaaijer, a geneticist and co-lead author of the study, explained that variations in genes, or alleles, can significantly affect how individuals respond to medications. Her co-author, Simon “Niels” Groen, also from UCR, emphasized the potential risks: “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.”

Global Implications of Underrepresentation

Clinical trials in the United States often follow the International Council for Harmonisation (ICH) standards, which facilitate consistency across studies. However, this focus has resulted in a concentration of research evidence from a limited number of regions, primarily the U.S., Europe, China, and Japan. Sub-Saharan Africa and much of Latin America represent less than 3% of pivotal trials, potentially omitting vital genetic variations that could inform drug development for millions of people in the U.S.

The landscape may soon change for Hispanic participants, as Brazil joined the ICH in 2016, followed by Mexico in 2021 and Argentina in 2024. These developments could enhance the representativeness of future clinical trials, ensuring that they better capture the genetic diversity present in global patient populations.

Zaaijer’s research journey began during her postdoctoral fellowship at Cornell Tech, where she examined the limited genetic diversity considered in preclinical drug models. “I kept wondering,” Zaaijer remarked, “If our preclinical models are this skewed, what happens once those drugs move into clinical trials?” She noted that biases in early research stages can have lasting effects on medical practice.

Recommendations for Future Trials

The findings, published in Communications Medicine, offer several recommendations aimed at improving diversity in clinical trials. These include setting diversity goals early in the drug development process, selecting testing sites that reflect local health needs and genetic backgrounds, and collecting biological samples to better understand individual responses to medications.

As DNA testing becomes more prevalent in healthcare settings, researchers stress that the realization of personalized medicine’s full potential relies on comprehensive data that considers ancestry from the outset. Groen asserted, “Precision medicine becomes possible only when clinical trials map the biology of all patients, not just a subset.”

This study serves as a critical call to action for the medical research community, highlighting the necessity for more inclusive and representative clinical trials as we move toward an era of personalized healthcare. The work of Zaaijer and Groen aims to provide a roadmap for achieving this essential goal, ensuring that all patients benefit from advancements in medicine.