FDA Data Shows Stunning Lack Of Diversity In U.S. Drug Trials

The melting pot of America apparently doesn’t include medicine

The future of medicine is supposed to be personal, but drug trial research suggests modern medicine has a lot of catching up to do in terms of American diversity. The clinical trials testing today’s breakthrough drugs still operate like it’s 1950.

Doctors increasingly talk about treatments tailored to individual genetics, medications calibrated to specific biology, and therapies designed around unique patient profiles. Unfortunately that doesn’t appear to be the reality (at least yet) for the majority of Americans.

A sweeping analysis of 341 pivotal clinical trials between 2017 and 2023 reveals that only 6% enrolled participants whose racial and ethnic makeup matched America’s population. This gap strikes at the heart of precision medicine’s core promise. When trials systematically exclude Black and Hispanic Americans, the genetic variants that affect how their bodies process medications never get studied, limiting the effectiveness of personalized treatments.

Sophie Zaaijer and Simon C. Groen analyzed data from the FDA’s Drug Trial Snapshots Program, tracking every Phase III trial that led to drug approval during this seven-year period. Their findings expose a contradiction: Medicine claims to be advancing toward individualized care while building that future on research that ignores millions of people who will need those treatments.

When Genetics Get Left Behind

Precision medicine depends on understanding how genetic differences influence drug response. Many genetic variants occur across all populations but at wildly different frequencies, making diverse trial enrollment essential for detecting these variations.

Take genes in the cytochrome P450 family, which help the body break down 60-80% of prescription drugs. One variant in a gene called CYP3A4 appears in 76.5% of people with African ancestry but only 2.78% of those with European ancestry. People carrying two copies of this variant metabolize certain drugs more slowly, reducing active compound levels in their bloodstream.

Research on breast cancer patients treated with cyclophosphamide shows how this genetic difference determines survival. Women with this variant show lower survival rates at standard doses because the drug doesn’t reach therapeutic levels. Trials dominated by White participants would completely miss this life-threatening pattern, leaving Black women at higher risk when the medication reaches the market.

The same principle applies across countless medications. Genes affecting drug metabolism, efficacy, and side effects vary in frequency across ancestral groups. Without representative trial cohorts, these variations remain invisible until patients start experiencing unexpected reactions or treatment failures.

Representation Is Getting Worse, Not Better

The study, published in Communications Medicine, uncovered troubling trends over time. Black participant representation peaked in 2019 but has declined since. Hispanic enrollment dropped steadily from 2017 through 2023, with a sharp decrease in 2020. Meanwhile, Asian representation increased and White enrollment remained stable.

Just 23% of trials in 2023 adequately represented Black participants. Only 30% properly enrolled Hispanic individuals. Asian participants appeared in appropriate numbers in 81% of trials, largely because pharmaceutical companies increasingly conduct research in Asian countries rather than demographic planning.

Looking at all 341 trials, only 20 represented all four major demographic groups according to their proportions in the US population. Another 89 trials represented three groups appropriately, 141 represented two groups, and 89 included adequate representation of just a single group. Two trials represented none of the groups according to FDA guidelines.

Geography Determines Who Gets Studied

Trial location emerged as the strongest predictor of participant diversity. Studies conducted entirely in the United States averaged 17.7% Black enrollment, a figure that actually exceeds the 13.7% proportion of Black individuals in the US population according to Census data. As trials moved overseas, Black representation dropped sharply.

The proportion of US-based trial participants climbed from 33% in 2017 to 47% in 2020, coinciding with improved Black representation. By 2023, however, that figure had dropped to 25%, tracking alongside the observed decline in Black enrollment.

Asian participation followed the opposite pattern. US-based trials averaged just 2.3% Asian enrollment, while international trials showed substantially higher numbers. This geographic divide reflects pharmaceutical companies’ strategic decisions about where to locate trial sites, which prioritize regulatory convenience and operational efficiency over demographic considerations.

China’s entry into the International Council for Harmonization—a regulatory body that sets global standards for drug trials—accelerated this shift in 2017. By 2023, China had doubled its share of global clinical trial activity, becoming a major research hub. This expansion improved Asian representation in aggregate trial data while simultaneously reducing opportunities for Black American enrollment.

The Regulatory Factor

Drug designation influenced representation patterns. Trials for Orphan drugs, which treat rare diseases affecting fewer than 65 per 100,000 people, showed consistently lower enrollment of Black and Hispanic participants compared to Non-Orphan drugs. These trials also conducted less research in the US.

Breakthrough Therapy designation produced notably different results. This expedited pathway applies to drugs treating serious conditions with preliminary evidence of substantial benefit. It led to more balanced enrollment across racial and ethnic groups. Underrepresentation of Black individuals dropped from 78.4% in Orphan drug trials to 63% when Breakthrough designation was added.

Trials with Breakthrough status also showed more consistent US-based participation, typically ranging from 20-40% rather than the all-or-nothing pattern seen elsewhere. This improvement likely stems from earlier FDA engagement during trial design, prompting sponsors to consider diversity from the outset rather than as a late addition.

About 72% of all trials received either Orphan or Priority designation, while 29% received Breakthrough status. Priority Review accelerates regulatory evaluation without influencing trial design and showed lower Black recruitment compared to drugs reviewed on standard timelines.

Disease Categories Show Stark Disparities

What condition a drug treats dramatically affects who enrolls in its trials. Psychiatric disorder trials achieved 38% Black enrollment with 89% of trial sites based in the US. Pain management trials reached 17% Black participation and were entirely US-based.

Cancer trials told a different story. Despite Black Americans experiencing the highest cancer mortality rates among racial groups, cancer drug trials averaged just 4% Black enrollment across 100 trials. Dermatology and endocrinology trials showed similarly low numbers.

Asian participants found highest representation in trials for autoimmune diseases, kidney diseases, and cancer treatments. Hispanic individuals appeared most frequently in trials for gastrointestinal disorders, reproductive health, and dermatology.

Infectious disease trials provided an exception to geographic patterns, enrolling 18% Black and 20% Hispanic participants despite only 35% US-based sites. This reflects the global distribution of infectious diseases like parasitic infections, which occur more frequently in Africa and Latin America.

The Path Forward

Pharmaceutical companies announced diversity commitments starting in 2020, evidenced by public Diversity, Equity, and Inclusion statements. That same year, the FDA released draft guidance on Diversity Action Plans, recommending sponsors submit these plans between filing an Investigational New Drug application and starting Phase III trials.

The guidance wasn’t mandatory, yet 91 sponsors voluntarily submitted plans during 2020-2021, with 84% coming from oncology divisions. Whether these initiatives translate into improved enrollment remains unclear. Drugs approved in 2023 reflect trials that may have begun in 2015, before these diversity efforts launched.

Reporting transparency has improved substantially. Between 96-100% of trials now document enrollment of White, Black, and Asian participants, while 90% report Hispanic enrollment. Actually achieving representative numbers, however, remains elusive.

Self-reported race and ethnicity create additional challenges. Trial participants select their demographic categories from predefined options rather than providing genetic verification. These labels serve as imperfect proxies for genetic ancestry, failing to capture important within-group variation. “Asian” encompasses dramatically different populations from East Asia versus South Asia. “Black” in the US may represent different ancestral backgrounds than in other countries.

Future trial design may eventually shift from self-reported demographics to biomarker-driven stratification based on specific genetic variants. This approach would bypass race and ethnicity as proxies, directly targeting the genetic differences that affect drug response. Until universal genomic profiling becomes standard practice, representative enrollment based on demographic categories offers the most practical path toward accounting for population-level genetic variation.

Precision medicine promises to deliver the right treatment to the right patient at the right time. That promise falters when the foundational research excludes the genetic diversity that makes precision necessary. Without fixing clinical trial enrollment, personalized medicine becomes personal only for those who happened to be included in the testing.

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