Diversity in Clinical Trials: Requirements, Enrollment Evidence, and How to Vet an Agency

What FDA's Diversity Action Plan rule requires, how far enrollment sits from representative, and what to ask before hiring an agency to close the gap.

Diversity in clinical trials is still rare by the numbers that matter most. Among 341 phase III pivotal trials behind FDA approvals from 2017 to 2023, only 6% enrolled a group that matched the US population across all four largest racial and ethnic groups [1].

The rules get misstated about as often as the numbers do. FDA's guidance on Diversity Action Plans still carried a draft label when we checked in September 2026 [2]. The plans themselves have been law since December 2022, when section 3601 of the Food and Drug Omnibus Reform Act made them a requirement for phase III and other pivotal studies [3].

Refero does not run recruitment campaigns. We vet and match the clinical research marketing agencies that do. What follows is for the person deciding whether thin enrollment is a site problem or an outreach problem, and what to ask before hiring anyone to fix it.

Clinical trial diversity statistics at a glance

Every figure here is sourced in full at the foot of the page.

• Only 6% of 341 phase III pivotal trials behind FDA approvals from 2017 to 2023 matched the US population across all four largest racial and ethnic groups [1].
• A 2025 analysis of cancer trial enrollment found trials enrolled 45% fewer Black patients than proportional representation would predict, and traced more than half of that shortfall to the choice of enrolling region and practice [4].
• A meta-analysis of 20 studies covering more than 70,000 people found minority groups no less willing to join health research than non-Hispanic whites [6].
• The most common reason cancer patients never join a trial is that no trial is open where they are treated (55.6%). Ineligibility comes next (21.5%). Only 14.8% reached an available, eligible trial and did not enroll, and 8.1% enrolled [7].
• The Diversity Action Plan requirement applies only to studies whose enrollment begins 180 days after FDA finalizes its guidance [2][3].

What diversity in clinical trials means

Representative enrollment means the people in a study look like the people who will use the product. Sponsors measure that by age, sex, race, and ethnicity against a reference such as the US Census, disease prevalence, or the condition's epidemiology. Three things get mixed together: reporting (whether a trial records race and ethnicity data at all), representation (whether enrolled numbers match the reference population), and inclusion practice (the eligibility rules, site locations, and participation burden that shape who can take part). What changed in December 2022 is that some of these expectations became a filing requirement in law [3].

Where the FDA diversity requirement stands

Section 3601 of the Food and Drug Omnibus Reform Act, signed in December 2022, requires sponsors of phase III or other pivotal studies to submit a Diversity Action Plan no later than the phase III protocol submission. The plan states enrollment goals by age group, sex, race, and ethnicity, gives the reasoning behind those goals, and describes how the sponsor intends to meet them. FDA can waive the requirement. The statute covers both drug and device pathways [3].

FDA published draft guidance on plan content in June 2024, under docket FDA-2021-D-0789, issued jointly by four centers. The draft covers format, content, timing, and the waiver process. FDA labels it as draft guidance, not for implementation, containing non-binding recommendations [2]. That label matters: a draft carrying non-binding recommendations is not the same instrument as a final rule, though plenty of sponsor-facing content treats it as settled.

The mandate is statutory but not yet enforceable against any specific trial. The law ties the requirement to studies whose enrollment begins 180 days after FDA publishes final guidance, and the guidance page still carried the June 2024 draft label as of this article's September 2026 check [2][3]. No sponsor is out of compliance today, but the statute is in force and the draft already sets out what a plan should contain. A sponsor planning a phase III protocol can write to the draft now rather than wait. The date to track is the trigger date, not the date the statute passed.

What the enrollment data shows about representation

Among 341 phase III pivotal trials behind FDA approvals from 2017 to 2023, just 6% matched the US population across all four largest racial and ethnic groups; in 2023 alone, Black enrollment was adequate in 23% of trials, Hispanic in 30%, and Asian in 81% [1]. Cancer trials show the same pattern: only 63% of the 230 trials behind cancer drug approvals from 2008 to 2018 reported race at all, and where it was reported, Black participants were 3.1% and Hispanic participants 6.1% of enrollees, or 22% and 44% of what their share of US cancer incidence would predict [5]. FDA does not publish a single percentage for participant diversity; its Drug Trials Snapshots report demographics per approval and per year, not as one running total [12].

Site selection or outreach: what actually decides who enrolls

Site selection, on the strongest evidence available. A 2025 analysis of cancer trial enrollment found trials enrolled 45% fewer Black patients than proportional representation would predict and traced more than half of that shortfall to the choice of enrolling region and practice [4]. A separate meta-analysis found the most common reason cancer patients never join a trial is that no trial was open at their institution (55.6%), with ineligibility next (21.5%) and patient refusal at most 14.8% [7]. A meta-analysis of 20 studies covering more than 70,000 people found minority groups no less willing to join health research than non-Hispanic whites [6]. Outreach can raise awareness among people who already have a qualifying trial within reach, but it cannot open a site in a community that has none or widen a protocol's eligibility criteria.

What improves representative enrollment

Four levers have evidence behind them, and they sit with different parties:

• Site placement in community and safety-net settings. The 2025 cancer analysis traced more than half of the Black-enrollment shortfall to region and practice choice [4]. This lever sits with the sponsor and site network, not with an agency.
• Broadened eligibility criteria. FDA's guidance on eligibility criteria, enrollment practices, and trial designs (final, November 2020; revised December 2025) recommends broadening criteria so trials enroll a representative population [13]. Criteria count is also one of the strongest protocol-level predictors of slow enrollment, per Refero's analysis of enrollment timelines and which recruitment strategies have evidence behind them. An agency does not write the protocol.
• Participation burden reduction. In CISCRP's 2025 survey, study visits at or close to home were rated the most helpful support (76%), followed by transportation (72%), caregiver support (70%), compensation (68%), and video visits (67%) [14]. This is the first lever an agency can genuinely influence.
• Community partnerships that pre-date the trial. The National Academies' 2022 consensus report recommends sustained engagement and accountability structures [15]. Campaign-length partnerships are not the same thing.

Language-concordant, IRB-reviewed materials are a floor rather than a lever: without them, non-English-speaking populations are shut out regardless of what else a sponsor does.

Three numbers to stop repeating

Diversity content recycles a handful of figures that do not survive a look at their sources. If a vendor's deck leans on these, that tells you something about the rest of the deck.

"Black Americans are 13% of the population but only 5% of clinical trial participants." That 5% comes from one year of FDA's Drug Trials Snapshots, not an all-trials figure. The percentage moves every year and by therapeutic area [12].

"Minorities are less willing to take part in research." A meta-analysis of 20 studies and more than 70,000 people found willingness among minority groups no lower than among non-Hispanic whites [6]. The barrier evidence shows most non-participation happens before anyone is asked [7].

"Fewer than 5% of cancer patients join a clinical trial." The 2019 meta-analysis of institution-level data put the overall rate at 8.1% and the single most common cause of non-participation at no trial being available, not refusal [7].

Every figure in this section, and everywhere else on this page, is checked against how Refero decides which figures it will publish before it runs.

How to choose an agency for representative recruitment

Four questions separate an agency that can move the numbers in this article from one that cannot. Each comes from the evidence above, not from a generic vendor checklist.

1. Is your representation strategy site selection or media? One large 2025 cancer analysis traced more than half of the Black-enrollment disparity to where trials were placed, not to how they were advertised [4].

2. For your last three trials in this indication, what was the demographic split of referrals versus randomizations, and how did you measure it? Representation that exists at referral and disappears by randomization is a screening problem the agency should own.

3. What do you do about participation burden: travel, compensation, language, visit schedule? Participants rate burden relief, from home or near-home visits to transportation and compensation, as the most helpful support they receive [14]. A Diversity Action Plan also has to say how goals will be met, not only what they are.

4. Can you show a redacted Diversity Action Plan you contributed to, with the goals as written next to the enrollment as delivered? Plans are inexpensive to write. The delivered split is the only evidence that the plan did anything.

Refero screens healthcare marketing and patient recruitment agencies against five published criteria and introduces up to three that fit your brief. It is free for buyers, and there is no obligation to hire anyone we introduce. Tell us what you need.

Frequently asked questions

What are the FDA diversity requirements for clinical studies?

FDA requires sponsors of phase III or other pivotal studies to submit a Diversity Action Plan under FDORA section 3601, signed into law in December 2022. The plan states enrollment goals by age, sex, race, and ethnicity, plus how the sponsor will meet them. The requirement applies only to studies whose enrollment begins 180 days after FDA finalizes its draft guidance, which had not happened as of September 2026.

Are Diversity Action Plans required right now?

Not yet in a binding sense. The requirement is law, but it applies only to studies whose enrollment starts 180 days after FDA publishes final guidance. As of this article's September 2026 check, no final version had replaced the June 2024 draft [2][3].

What is the racial breakdown of clinical trial participation?

There is no single official figure. Among 341 phase III pivotal trials behind FDA approvals from 2017 to 2023, only 6% matched the US population across all four largest racial and ethnic groups. In 2023 trials, Black enrollment was adequate in 23%, Hispanic in 30%, and Asian in 81% [1].

What are the barriers to diversity in clinical trials?

The largest barrier is structural. The most common reason cancer patients did not take part was that no trial was open where they were treated (55.6%), followed by protocol ineligibility (21.5%). Only 14.8% reached an available, eligible trial and did not enroll [7].

Does site selection or outreach matter more for representative enrollment?

Site selection. A 2025 analysis traced more than half of the Black-enrollment shortfall in cancer trials to the choice of enrolling region and practice [4]. Outreach can raise awareness among patients who already have a trial within reach but cannot create a site where none exists or widen eligibility criteria.

Sources

• Zaaijer S, Groen SC. Longitudinal clinical trial enrollment trends across 341 US FDA-approved drugs and their guiding role in precision medicine strategies. Communications Medicine, 2025;5:514. Link
• US Food and Drug Administration. Diversity Action Plans to Improve Enrollment of Participants from Underrepresented Populations in Clinical Studies, Draft Guidance for Industry. FDA, 2024. Link
• US Congress. Consolidated Appropriations Act, 2023, Public Law 117-328, Division FF, Title III, Subtitle F, Sections 3601 (Diversity Action Plans for Clinical Studies) and 3602 (Guidance on Diversity Action Plans for Clinical Studies, including the 180-day applicability clause). December 29, 2022. Link
• Shah SJ, Manz CR, Balthis B, Raman HS, Abaluck J, Keating NL, Agha L. The role of regional and practice trial sites in nonrepresentative randomized cancer trial enrollment. Journal of the National Cancer Institute, 2025;117(12):2672-2676. Link
• Loree JM, Anand S, Dasari A, et al. Disparity of Race Reporting and Representation in Clinical Trials Leading to Cancer Drug Approvals From 2008 to 2018. JAMA Oncology, 2019;5(10):e191870. Link
• Wendler D, Kington R, Madans J, et al. Are Racial and Ethnic Minorities Less Willing to Participate in Health Research? PLoS Medicine, 2006;3(2):e19. Link
• Unger JM, Vaidya R, Hershman DL, Minasian LM, Fleury ME. Systematic Review and Meta-Analysis of the Magnitude of Structural, Clinical, and Physician and Patient Barriers to Cancer Clinical Trial Participation. Journal of the National Cancer Institute, 2019;111(3):245-255. Link
• US Food and Drug Administration. Collection of Race and Ethnicity Data in Clinical Trials, Guidance for Industry and FDA Staff. FDA, 2016. Link
• National Institutes of Health. Inclusion of Women and Minorities as Participants in Research Involving Human Subjects. NIH Grants and Funding. Link
• Turner BE, Steinberg JR, Weeks BT, Rodriguez F, Cullen MR. Race/ethnicity reporting and representation in US clinical trials: a cohort study. The Lancet Regional Health, Americas, 2022;11:100252. Link
• Bierer BE, Meloney LG, Ahmed HR, White SA. Advancing the inclusion of underrepresented women in clinical research. Cell Reports Medicine, 2022;3(4):100553. Link
• US Food and Drug Administration. Drug Trials Snapshots. FDA. Link; 2020 Drug Trials Snapshots Summary Report, February 2021. Link
• US Food and Drug Administration. Enhancing Participation in Clinical Trials: Eligibility Criteria, Enrollment Practices, and Trial Designs, Guidance for Industry. Final guidance, December 2025 (first revision of the November 2020 guidance Enhancing the Diversity of Clinical Trial Populations), docket FDA-2019-D-1264. Link
• CISCRP. 2025 Perceptions and Insights Study: Participation Experiences report. CISCRP, 2025. Link (study index: Link)
• National Academies of Sciences, Engineering, and Medicine. Improving Representation in Clinical Trials and Research: Building Research Equity for Women and Underrepresented Groups. The National Academies Press, 2022. Link