Here’s a shocking truth: the medications we rely on might not work for everyone, and it’s largely because clinical trials don’t reflect America’s diverse population. A groundbreaking study reveals that a staggering 94% of clinical trials used to approve new drugs in the U.S. fail to represent the country’s racial and ethnic makeup. Even more concerning? The gap is widening, particularly for Black and Hispanic individuals, whose representation has been declining since 2021. But here’s where it gets controversial: while personalized medicine promises treatments tailored to our genetic makeup, the very foundation of this approach—clinical trials—is missing critical genetic variations that could determine safety and effectiveness.
Researchers from UC Riverside and UC Irvine analyzed 341 pivotal trials—the large, final-stage studies required for FDA approval—between 2017 and 2023. Their findings are eye-opening: Black and Hispanic enrollment dropped during a period when calls for equity in science and medicine were louder than ever. Meanwhile, Asian representation increased, and white participation remained steady. This imbalance isn’t just a numbers game; it’s a matter of health equity. Precision medicine depends on understanding how genetic differences impact treatment outcomes. If trials overlook large segments of human genetic variation, we risk missing vital clues about a drug’s safety and efficacy.
Sophie Zaaijer, a geneticist at both UCR and UC Irvine, and Simon 'Niels' Groen, a UCR geneticist, argue that while ancestry shouldn’t be the sole factor in treatment decisions, it plays a pivotal role in early drug development. Different populations often carry unique gene variants, called alleles, that influence how their bodies respond to medications. As Groen puts it, '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.' And this is the part most people miss: the lack of diversity in trials isn’t just a scientific oversight—it’s a systemic issue that perpetuates health disparities.
Clinical trials for U.S.-approved drugs are conducted both domestically and in countries following International Council for Harmonisation (ICH) standards. While this ensures consistency and speeds up approvals, it also concentrates evidence in regions like the U.S., Europe, China, and Japan. Sub-Saharan Africa and much of Latin America, which host fewer than 3% of pivotal trials, are often excluded from the data shaping medicines used by millions. But there’s a glimmer of hope: countries like Brazil (2016), Mexico (2021), and Argentina (2024) have joined ICH, potentially expanding trial networks to underrepresented regions and improving global genetic representation.
Zaaijer’s journey into this research began at Cornell Tech, where she studied how preclinical drug development often overlooks human genetic diversity. 'I kept wondering,' she said, 'If our preclinical models are this skewed, what happens once those drugs move into clinical trials?' Bias in preclinical models is a warning sign, but bias in clinical trials becomes medical practice. Her collaboration with Groen’s lab was a natural fit. Groen’s team studies how tiny worms metabolize plant toxins, and the parallels with human biology are striking. 'Many of the same genes used to break down chemicals in worms are also involved in drug metabolism in humans,' Groen explained. 'Small natural variations in these genes can have a big effect.'
Published in Communications Medicine, the study offers actionable recommendations: set diversity goals from the preclinical stage, choose trial locations that reflect local health needs and genetic backgrounds, and collect biological samples to better understand how bodies react to drugs. Even as DNA testing becomes more common, the researchers emphasize that personalized medicine’s full potential can only be realized with stronger, more ancestry-aware data from the start. '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.'
Controversial Question: Should drug approvals be paused until clinical trials better represent the genetic diversity of the populations they aim to serve? Share your thoughts in the comments—this is a conversation we can’t afford to ignore.
