Why Diversity in Clinical Trials Matters
Despite accounting for nearly 40% of the U.S. population, non-white racial and ethnic groups comprised only 25% of participants in clinical trials for novel drugs approved in 2020 3 .
Imagine a world where the dosage instructions on medication bottles came with an invisible asterisk: "This may work differently for you—we haven't tested it on people like you." This isn't science fiction; it's the reality for millions of people who don't see themselves represented in clinical trials.
Despite accounting for nearly 40% of the U.S. population, non-white racial and ethnic groups comprised only 25% of participants in clinical trials for novel drugs approved in 2020 3 . This representation gap isn't just a matter of fairness—it's a fundamental scientific problem that affects how well medicines work for everyone who uses them.
The consequences of this gap are far from theoretical. Consider the case of BiDil, a heart failure drug that initially failed in large clinical trials. Years later, researchers discovered it reduced heart failure deaths in African American patients by 43%. Had the original trials included more diverse participants, this life-saving benefit might have been recognized years earlier 2 . Stories like this reveal a troubling truth: when clinical trials lack diversity, we don't just miss opportunities—we risk missing treatments that could save lives.
The assumption that drugs work identically in all bodies doesn't hold up to scientific scrutiny. Sex-dependent differences in renal clearance, body weight, and body fat percentage significantly affect how drugs are processed in the body 1 .
For example, CYP3A4 enzyme activity is 20-50% higher in women, resulting in faster clearance of drugs metabolized through this pathway 1 . This means the same pill can have different concentrations and effects in women versus men.
Ethnicity encompasses cultural expression, religion, shared beliefs, and practices that can significantly influence health outcomes 1 .
Simultaneous use of other medications, dietary patterns, and health behaviors may vary across ethnic groups, contributing to differences in treatment outcomes 1 .
This complex interplay between biology, environment, and culture means that truly understanding a treatment's effectiveness requires testing across the full spectrum of human diversity.
To understand how diversity in clinical trials has evolved, researchers conducted a systematic review of clinical drug trials published in two prominent journals comparing two time periods: 2000-2001 and 2020-2021 1 .
This comprehensive analysis examined 281 articles representing 17,639 research participants, tracking not only participant demographics but also the diversity of the researchers conducting the studies.
Articles Analyzed
Research Participants
| Time Period | Female Participants | Female First Authors | Female Last Authors |
|---|---|---|---|
| 2000-2001 | ~33% | Not specified | Not specified |
| 2020-2021 | ~33% | <40% | <40% |
The analysis revealed that sex representation has stagnated over two decades, with women consistently comprising only about one-third of research participants despite making up roughly half the population 1 .
White Representation
Black Representation
Asian Representation
Native American Representation
While representation of Black and Asian participants improved over the 20-year period, significant gaps remain, particularly for Native American populations 1 .
The burn unit might seem like an unlikely place to examine clinical trial diversity, but a 2025 cross-sectional study of burn randomized controlled trials reveals a familiar pattern. The analysis found females comprised just 37.02% of participants, significantly underrepresented relative to their real-world burn burden 5 .
Even more concerning: only 9 of 39 trials reported race data, and just 7 reported ethnicity—a startling transparency failure that makes it impossible to assess whether trials serve the people most affected by these devastating injuries 5 .
Similar patterns emerge across specialties. In myositis clinical trials, Black, Asian, and Hispanic or Latino participants accounted for just 3%, 7%, and 2% of enrollees, respectively .
A 2025 analysis of ClinicalTrials.gov records revealed that 44.8% of studies failed to report race or ethnicity data altogether 6 .
While reporting has improved—rising from 7.4% in 2013 to 54.6% in 2024—the fact that nearly half of all studies still don't report this fundamental information highlights systematic failures in diversity tracking and accountability 6 .
| Study Characteristic | Effect on Reporting Likelihood |
|---|---|
| Study Type | Observational studies less likely to report than interventional trials |
| Trial Phase | Phase 4 trials least likely to report |
| Funding Source | NIH-funded studies more likely to report than industry-funded |
| Time Trend | Reporting has significantly improved since 2009 |
Meaningful progress requires moving beyond token inclusion to genuine partnership with underrepresented communities.
Patients are more comfortable participating in trials when their own doctors are involved as sub-investigators 2 .
Partnering with churches, advocacy groups, and local clinics introduces clinical trials in culturally sensitive environments with trusted community leaders 2 .
Diversity efforts don't end with recruitment—creating environments where all patients feel respected requires training in cultural humility, implicit bias, and communication strategies 2 .
Innovative approaches are leveraging technology to address diversity gaps.
Companies like Flatiron are using real-world data from diverse patient populations to inform trial design and site selection, helping sponsors understand disease progression and outcomes across underrepresented populations 7 .
Platforms like Medidata's Diversity Suite use industry-wide, site-level data to identify sites that have historically succeeded in enrolling diverse patients 4 .
Offering evening and weekend hours, combining visits, and providing clear directions and parking information can significantly enhance accessibility for working individuals and those with transportation challenges 2 .
The lack of diversity in clinical trials isn't merely a statistical problem—it's a quality-of-science issue with real-world consequences for patient safety and treatment effectiveness.
When clinical trials fail to represent the full spectrum of humanity, the resulting data are incomplete, potentially putting entire populations at risk of ineffective treatments or unexpected side effects 2 3 .
The goal isn't just checking diversity boxes—it's producing better science that leads to safer, more effective treatments for everyone.
The scientific community stands at a pivotal moment. Regulatory guidance like the FDA's Diversity Action Plans represents progress, but genuine change requires commitment at every level—from funders and research institutions to individual investigators 2 7 .
The next time you read about a medical breakthrough, consider asking: "Who was this tested on?" The answer might reveal more about the treatment's relevance to you than the breakthrough itself.