Only 6% of FDA drug trials reflect America's actual diversity

A new study reveals a stark mismatch: clinical trials used to approve drugs in the US include just 6% of participants from Black and Hispanic backgrounds—far below their share of the population. Worse, enrollment of these groups has actually declined since 2021, even as the medical establishment publicly committed to greater equity.

Researchers at UC Riverside and UC Irvine analyzed 341 pivotal trials—the large, final-stage studies that determine whether the FDA approves a new drug—between 2017 and 2023. What they found was a troubling pattern. While Asian representation increased and white participation stayed stable, Black and Hispanic enrollment dropped noticeably starting in 2021. The gap matters more than it might seem.

Why genetic diversity in trials actually changes what drugs do

Precision medicine—the emerging approach of tailoring treatments to individual genetics—depends entirely on understanding how different people's bodies respond to the same drug. "If clinical trials under-sample large segments of human genetic variation, critical signals for safety and efficacy may be missed," says Sophie Zaaijer, a geneticist and co-lead author of the study.

Here's the practical reality: people from different genetic backgrounds often carry different versions of genes that affect how their bodies metabolize medications. A drug that works safely for one population might cause serious side effects in another, or simply fail to work at all. When trials include only a narrow slice of humanity, doctors and patients downstream have incomplete information about whether a treatment is actually safe and effective for them.

Simon Niels Groen, the study's other lead author, puts it plainly: "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."

The geography problem nobody's talking about

The issue extends beyond race and ethnicity. Clinical trials happen in countries that follow International Council for Harmonisation standards—a system designed to ensure consistency and speed up approvals. But this has a side effect: evidence concentrates in a handful of regions. The US, Europe, China, and Japan dominate the data. Sub-Saharan Africa and much of Latin America, which together represent enormous genetic diversity and disease burden, host less than 3% of pivotal trials.

That's beginning to shift. Brazil joined ICH in 2016, Mexico in 2021, and Argentina in 2024. Expanding trial networks into these regions could help future studies capture the genetic variation of patients worldwide—and ensure drugs work for the people who actually need them.

The researchers propose concrete steps: set diversity goals early in drug development, choose trial locations that reflect local health needs and genetics, and collect biological samples that help researchers understand how different bodies respond to treatment. "Precision medicine becomes possible only when clinical trials map the biology of all patients, not just a subset," Groen says.

The infrastructure for more inclusive trials exists. What's needed now is the commitment to use it.