Sex of Participants in NIH-Funded Research
Data Brief
The current data brief details the sex of participants in research funded by the National Institutes of Health (NIH) between 1995 and 2025.
In three ways, this data brief updates a previous data brief published at The Nuzzo Letter. First, data from 2023 to 2025 have been added. Second, the number of enrollments (extramural plus intramural) is now shown along with proportional representations. Third, data from each NIH Institute are presented.
The NIH publishes these data as “enrollments” rather than number of “participants,” because a participant could be enrolled in more than one NIH-funded trial. Thus, I present the data as “enrollments” rather than “participants.” However, dual enrollments in NIH-funded trials are probably not frequent enough to alter the data significantly. So, I sometimes use the words “enrollments” and “participants” interchangeably, depending on the context.
For most graphs, enrollment numbers or counts align with the left y-axis, with distinct lines presented for male enrollments, female enrollments, and enrollments in which participant sex was unknown to the NIH. Also, for most graphs, the percent of enrollments who were female (i.e., “female representation”) is shown via vertical bars that align with the right y-axis.
For the Institute-specific analysis, data were only available for the years 2013 to 2024.
Do not forget to scroll to the bottom of this page to seem my Bonus Commentary, and if you appreciate this content, and want to see more content like it, consider supporting The Nuzzo Letter with a one-time or recurring donation. Thank you!
All NIH Institutes Combined (Version 1)
Between 1995 and 2025, female enrollments exceeded male enrollments in NIH-funded research each year, except in 2017, when female enrollments accounted for 47.2% of enrollments.
In most years, there were roughly 2-3 million more female than male enrollments in NIH-funded research, with an average of 2.5 million more female than male enrollments each year over the approximate 30-year period.
Between 1995 and 2025, the average annual distribution of NIH-funded research enrollments was 58% female, 40% male, and 2% unknown sex (see also Version 2 below).
All NIH Institutes Combined (Version 2)
Like the graph above, the graph below shows the proportion of enrollments whose sex was female, but it also shows the proportions of enrollments whose sex was male or unknown. It also shows the average of the proportional representations for females (58%), males (48%), and unknown sex (2%) across all years (see the bar on the far right of the graph).
For 2023, the source provided only the proportion of enrollments who were female, and I was unable to find relevant data for 2024.
Representation of Female Participants by NIH Institute (2016 & 2024)
Of the 21 NIH Institutes reporting research inclusion data in 2016, 15 reported over 50% female representation in enrollments and six reported over 60% female representation in enrollments.
Of the 21 NIH Institutes reporting research inclusion data in 2024, 18 reported over 50% female representation in enrollments and four reported over 60% female representation in enrollments.
National Cancer Institute (NCI)
Between 2013 and 2024, female enrollments exceeded male enrollments in NCI-funded research each year, except in 2017, when female enrollments accounted for 44.5% of enrollments.
Between 2013 and 2024, the average annual distribution of NCI-funded research enrollments was 59.3% female, 38.5% male, and 2.2% unknown sex.
National Eye Institute (NEI)
Between 2016 and 2024, female enrollments exceeded male enrollments in NEI-funded research every year.
Between 2016 and 2024, the average annual distribution of NEI-funded research enrollments was 54.7% female, 44.1% male, and 1.1% unknown sex.
National Human Genome Research Institute (NHGRI)
Between 2016 and 2021, female and male enrollments in NHGRI-funded research were roughly equal, whereas, between 2022 and 2024, female enrollments exceeded male enrollments.
Between 2016 and 2024, the average annual distribution of NHGRI-funded research enrollments was 51.0% female, 44.4% male, and 37.8% unknown sex.
National Heart, Lung, and Blood Institute (NHLBI)
Between 2013 and 2024, female enrollments exceeded male enrollments in NHLBI-funded research every year.
Between 2013 and 2024, the average annual distribution of NHLBI-funded research enrollments was 55.2% female, 42.6% male, and 2.2% unknown sex.
National Institute on Aging (NIA)
Between 2013 and 2024, female enrollments in NIA-funded research exceeded male enrollments in most years, but male enrollments exceeded female enrollments in 2017, 2018, and 2019.
Between 2013 and 2024, the average annual distribution of NIA-funded research enrollments was 52.3% female, 46.8% male, and 0.8% unknown sex.
National Institute on Alcohol Abuse and Alcoholism (NIAAA)
Between 2013 and 2024, male enrollments in NIAAA-funded research exceeded female enrollments prior to 2021 but not in 2021 or after.
Between 2013 and 2024, the average annual distribution of NIAAA-funded research enrollments was 38.1% female, 53.6% male, and 8.3% unknown sex.
In 2016 and 2017, the proportion of enrollments in NIAAA-funded research whose sex was unknown was unusually high. This was because the NIAAA funded two large survey studies in 2016 and 2017 that did not record participant sex.
In 2018, male enrollments were substantially higher than female enrollments because the NIAAA funded a large observational study of military veterans (160,415 males and 4,241 females).
National Institute of Allergy and Infectious Diseases (NIAID)
Between 2013 and 2024, female and male enrollments in NIAID-funded research were roughly equal.
Between 2013 and 2024, the average annual distribution of NIAID-funded research enrollments was 49.9% female, 46.5% male, and 3.6% unknown sex.
National Institute of Arthritis and Musculoskeletal and Skin Diseases (NIAMS)
Between 2013 and 2024, female enrollments exceeded male enrollments in NIAMS-funded research every year.
Between 2013 and 2024, the average annual distribution of NIAMS-funded research enrollments was 60.5% female, 37.8% male, and 1.7% unknown sex.
National Institute of Biomedical Imaging and Bioengineering (NIBIB)
Participant sex was unknown for a large amount NIBIB-funded research conducted between 2017 and 2021.
With that limitation in mind, between 2013 and 2024, the average annual distribution of NIBIB-funded research enrollments was 41.5% female, 32.7% male, and 25.8% unknown sex.
National Institute of Child Health and Human Development (NICHD)
Between 2013 and 2024, female enrollments in NICHD-funded research trials exceeded male enrollments every year except in 2014. In 2014, many enrollments were classified as “unknown” sex. This occurred because the NICHD funded a large survey study in India, where “the approved study design precluded accurate identification by gender.”
With that anomaly in mind, between 2013 and 2024, the average annual distribution of NICHD-funded research enrollments was 61.9% female, 32.2% male, and 5.9% unknown sex.
National Institute on Drug Abuse (NIDA)
Between 2016 and 2024, male enrollments exceeded female enrollments in NIDA-funded each year, except in 2022, when female enrollments accounted for 51.5% of enrollments.
Between 2016 and 2024, the average annual distribution of NIDA-funded research enrollments was 46.8% female, 51.5% male, and 1.8% unknown sex.
National Institute on Deafness and Other Communication Disorders (NIDCD)
Between 2013 and 2024, female enrollments in NIDCD-funded research exceeded male enrollments in some years, whereas the opposite was true in other years.
Between 2013 and 2024, the average annual distribution of NIDCD-funded research enrollments was 49.8% female, 46.8% male, and 3.4% unknown sex.
National Institute of Dental and Craniofacial Research (NIDCR)
Between 2013 and 2024, female enrollments exceeded male enrollments in NIDCR-funded research every year.
Between 2013 and 2024, the average annual distribution of NIDCR-funded research enrollments was 55.0% female, 42.4% male, and 2.6% unknown sex.
National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK)
Between 2013 and 2024, female enrollments exceeded male enrollments in NIDDK-funded research every year.
Between 2013 and 2024, the average annual distribution of NIDDK-funded research enrollments was 51.3% female, 43.9% male, and 4.8% unknown sex.
National Institute of Environmental Health Sciences (NIEHS)
Between 2013 and 2024, female enrollments exceeded male enrollments in NIEHS-funded research every year.
Between 2013 and 2024, the average annual distribution of NIEHS-funded research enrollments was 67.8% female, 31.0% male, and 1.2% unknown sex.
National Institute of General Medical Sciences (NIGMS)
Between 2013 and 2024, female enrollments exceeded male enrollments in NIGMS-funded research every year.
Between 2013 and 2024, the average annual distribution of NIGMS-funded research enrollments was 57.9% female, 39.3% male, and 2.8% unknown sex.
National Institute of Mental Health (NIMH)
Between 2013 and 2024, female enrollments in NIMH-funded research exceeded male enrollments in some years, whereas male enrollments exceeded female enrollments in other years.
Between 2013 and 2024, the average annual distribution of NIMH-funded research enrollments was 51.5% female, 41.1% male, and 7.4% unknown sex.
National Institute on Minority Health and Health Disparities (NIMHD)
Between 2016 and 2024, female enrollments exceeded male enrollments in NIMHD-funded research in all but one year.
The high proportion of participants in 2024 whose sex was “unknown” was said by NIMHD to be due to “internet-based studies or studies using electronic health records.”
Between 2016 and 2024, the average annual distribution of NIMHD-funded research enrollments was 53.8% female, 42.5% male, and 3.6% unknown sex.
National Institute of Neurological Disorders and Stroke (NINDS)
Between 2013 and 2024, female and male enrollments in NINDS-funded research were roughly similar. Female enrollments exceeded male enrollments in some years, whereas male enrollments exceeded female enrollments in other years.
Between 2013 and 2024, the average annual distribution of NINDS-funded research enrollments was 51.3% female, 46.0% male, and 2.7% unknown sex.
National Institute of Nursing Research (NINR)
Between 2013 and 2024, female enrollments exceeded male enrollments in NINR-funded research every year.
Between 2013 and 2024, the average annual distribution of NINR-funded research enrollments was 64.0% female, 34.3% male, and 1.7% unknown sex.
National Library of Medicine (NLM)
Male enrollments exceeded female enrollments in NLM-funded research between 2013 and 2018, whereas female enrollments exceeded male enrollments between 2019 and 2024.
The larger proportion of participants whose sex was recorded as “unknown” in 2024 appears to have been the result of a large trial in which such data were not reported.
Between 2013 and 2024, the average annual distribution of NLM-funded research enrollments was 48.7% female, 43.7% male, and 7.6% unknown sex.
Sources
Data from 2013 to 2024 for individual NIH Institutes were obtained from the NIH’s Research Portfolio Online Report Tools (RePORT) under the topic “Inclusion.”
Data from 1995 to 2002 for the NIH were obtained from: National Institutes of Health. (2008). Monitoring Adherence to the NIH Policy on the Inclusion of Women and Minorities as subjects in Clinical Research: Comprehensive Report: Tracking of Human Subjects Research as Reported in Fiscal Year 2006 and Fiscal Year 2007.
Data from 2003 to 2011 for the NIH were obtained from: Office of Research on Women’s Health. (2013). Report of the Advisory Committee on Research on Women’s Health, Fiscal Years 2011–2012: Office of Research on Women’s Health and NIH Support for Research on Women’s Health. Bethesda, MD: U.S. Department of Health and Human Services, Public Health Service, National Institutes of Health.
Data from 2012 to 2022 for the NIH were obtained from: Office of Research on Women’s Health. (2023). Report of the Advisory Committee on Research on Women’s Health, Fiscal Years 2021–2022: Office of Research on Women’s Health and NIH Support for Research on Women’s Health. Bethesda, MD: U.S. Department of Health and Human Services, Public Health Service, National Institutes of Health.
Data from 2023 for the NIH were obtained from: 60th Meeting of the National Institutes of Health (NIH) Advisory Committee on Research on Women’s Health (ACRWH) Office of Research on Women’s Health (ORWH) Bethesda, MD. April 9, 2024. Also, the percent of female participants in 2023 was confirmed in a press release published by the NIH Office of Extramural Research on May 21, 2024, titled “Reminders, Updates, and Some Data for Participant Inclusion.”
Data from 2025 for the NIH were obtained from: National Institutes of Health. (2026, May 27). FY25 Enrollment Data from NIH-supported Clinical Research Now Available. NIH Grants & Funding - NIH Extramural Nexus (News).
Bonus Commentary
Over the years, many academics, writers, commentators, and lobbyists have claimed that females are “underrepresented” in medical science and that women’s health has been ignored by medical researchers. For example, one recent editorial, which was written by the Chief Science Officer of the Society for Women’s Health Research and published in the academic journal Biology of Sex Differences, claimed that women have “been systematically excluded from participating in clinical trials.”
As the NIH’s data show, such claims are untrue. The NIH’s data show that women were over 50% of enrollments in NIH-funded research each year between 1995 and 2025, except in 2017. Over those three decades, females accounted for 58% of enrollments in NIH-funded research.
Even as early as 1994, staffers at the NIIH’s Office of Research on Women’s Health were admitting that “[l]ittle, if any, evidence is available that demonstrates that women have been systematically excluded from biomedical research.” That same year, the Institute of Medicine reached a similar conclusion. Then, in 2001, Ed Bartlett, now of the International Coalition for Men and Boys, published a paper in the journal Epidemiology titled, “Did Medical Research Routinely Exclude Women? An Examination of the Evidence.” Bartlett searched various medical research databases, tallying the studies in the 1960s, 1970s, 1980s, and 1990s that included males and/or females as participants. From the results, Bartlett concluded: “1) Historically, women were routinely included in medical research, and 2) Women have participated in medical research in numbers at least proportionate to the overall female population.” (NB. See my recent video discussion with Bartlett, Tom Golden, Jack Kammer, and Ed Stephens about Bartlett’s 2001 paper and the history behind that claims that women’s health has been “understudied” and “underfunded.”)
The NIH is the world’s leading public funder of biomedical research, and the NIH and ORWH routinely monitor and report demographic information about individuals who participate in NIH-funded trials. In fact, this monitoring and reporting was one of the mains reasons why the ORHW was created in 1990. Thus, it is bizarre that the women’s health lobby, and their associates in academia and the media, refuse to familiarize themselves with these publicly available data, as it was their ilk who originally insisted that these data be collected, monitored, and reported. In my opinion, the NIH’s data should be the starting point in conversations about male and female representations in health and medical research.
In the current data brief, I also presented Institute-specific data on participant sex between 2013 and 2024. The Institutes that consistently enrolled more female than male participants were the National Institute of Environmental Health Sciences (NIEHS) (67.8% female), the National Institute of Nursing Research (NINR) (64.0% female), the National Institute of Child Health and Human Development (NICHD) 61.9% female), the National Cancer Institute (NCI) (59.3% female), the National Institute on Minority Health and Health Disparities (53.8% female), and the National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK) (51.3% female). The greater female than male representation in NCI-funded research is peculiar, given that more males than females in the U.S. die by cancer each year. Also, the greater representation of females (49.8%) than males (46.8%) in research funded by the National Institute on Deafness and Other Communication Disorders (NIDCD) is peculiar, considering that hearing impairments and communication disorders are generally more common among U.S. males than U.S. females.
Finally, a claim about women’s health that often coincides with the assertion that women are “understudied,” “under-researched,” and “underrepresented” is that women’s health research is “underfunded.” This claim is also untrue. Each year, the NIH invests nearly twice as much money into sex-specific research on women’s health than it does on sex-specific research on men’s health. In fact, the NIH’s greater investment into sex-specific research on women’s than men’s health probably helps to explain why more females than males were enrolled in NIH-funded research over the past 30 years. Notably, this greater investment in women’s than men’s health research has occurred against a backdrop of significantly shorter life expectancy among U.S. males than females.
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Excellent data brief, especially the charts.
Over this three-decade period, there have been 58% female and 40% male participants. Hence, there have been 45% more women than men in these clinical trials:
58 divided by 40 = 1.45
Exceptional work here from James Nuzzo and The Nuzzo Letter...