Why the Gender Health Gap Still Exists

Medicine was built on evidence that left women out. The rules have changed since then, but the evidence has not caught up.

The gender health gap still exists because the evidence medicine runs on was gathered mostly from men, and rewriting evidence takes far longer than rewriting a rule. In 1977, a US guideline recommended excluding women who could become pregnant from early drug trials, a precaution taken after thalidomide [1][2]. The recommendation was reversed in 1993 [1]. Dosing decisions and animal research built on mostly male data are still being corrected. Across hundreds of diseases, women are also older than men at first diagnosis [3], and female-specific conditions other than cancer receive less than 2% of healthcare research and innovation funding [4]. In 2026, the EU and the US both announced new steps [5][6].

This post explains where the gap came from, where it shows up today and what is changing. Where a study measures something, we give the number.

It started with a precaution

In the early 1960s, thalidomide, a medicine taken during pregnancy, was found to cause severe birth defects. The US tightened drug regulation in 1962 [2]. In 1977, the FDA recommended that women who could become pregnant be excluded from phase 1 and early phase 2 trials until reproductive toxicity studies were done and some evidence of effectiveness existed [1]. The reasoning was protective. A drug could harm a fetus, and early trials offered no clearly stated medical benefit [1].

The effect was exclusion from the first studies, where a drug’s safety and dose are set. Researchers have pointed out that including women early matters for designing the later, larger trials [7].

A second assumption sat beside the precaution: that female bodies add variability and make research harder. Reviews have not borne that out. In the measures analysed, females were no more variable than males [8].

The rules changed in 1993

The NIH has required the inclusion of women in the research it funds since 1986, and the NIH Revitalization Act of 1993 made that law [1]. That same year, the FDA published a guideline that reversed its 1977 recommendation [1].

Changing a rule does not change what was already learned. A 2011 analysis found that fewer than a third of studies that the NIH required to analyse results by sex had published an analysis by sex [8].

Dosing is where the gap shows

In January 2013, the FDA required lower recommended doses of zolpidem sleep medicines. For women, the dose of immediate-release products fell from 10 mg to 5 mg [9]. The reason was that women clear zolpidem more slowly, so more of it remains in the blood the next morning and can impair driving [9]. In 2011, about 9 million people received zolpidem products from US outpatient pharmacies, and 63% of them were women [10].

A 2020 analysis of 86 drugs found that 76 produced higher drug exposure in women. Women experienced adverse drug reactions nearly twice as often as men, and for the 59 drugs with identifiable reactions, sex differences in how the body handles the drug predicted the direction of the difference in reactions in 88% of cases [11]. The authors recommend evidence-based dose reductions for women [11].

The pattern does not always point the same way. As one researcher noted, phase 3 studies of the drug tirilazad failed because the team had not recognised early that women needed higher doses than men [7]. In both stories, the difference came to light after the dose had been set.

The animals and cells were mostly male too

Clinical trials are one part of the evidence. A 2009 survey of research on mammals across 10 biological fields found male bias in eight of them. In neuroscience, studies of only male animals outnumbered studies of only females 5.5 to 1 [12]. Only 28% of the 841 studies surveyed used both sexes [13].

Since January 2016, NIH grant applicants who study vertebrate animals have had to explain how their design will account for sex as a biological variable [14]. A 2020 follow-up found that more studies included both sexes across nine disciplines. In eight of those disciplines, the share of studies that analysed data by sex had not changed [15].

Women are in more trials, and still not in proportion

Headline numbers have improved. Among more than 60,000 participants in the pivotal trials behind nearly 100 cancer drugs approved by the FDA between 1998 and 2018, 40.7% were women [16]. A fairer measure compares women’s share of participants with their share among patients. By that measure, women were under-represented in 66.9% of those trials, and sex-based safety data were reported in only 4.0% [16]. The share of women recruited did not change over time [16].

Cardiovascular trials published from 2018 to 2024 look similar. Women were 38.5% of participants, and the median participation-to-prevalence ratio was 0.77 [17]. A ratio of 1.0 would mean women take part in proportion to how many have the disease. The authors found a modest improvement towards 2024 [17].

Women are diagnosed later

A 2019 study of 6.9 million people in Denmark found that women were older than men at first diagnosis for 770 diseases, by about four years on average [3]. The researchers do not yet know whether genetics, environment, diagnostic criteria or a mix explains it [3]. The study measures age at first diagnosis, so it shows a gap, not how long any one person waited.

Endometriosis shows what a long wait looks like for one condition. It affects around 1 in 10 women of reproductive age [18]. A 2024 review of studies put the average diagnostic delay at 6.8 years, with a range from 1.5 to 11.4 years [19]. NICE puts the UK average at 9 years and 4 months [18].

Funding follows evidence, and evidence follows funding

A 2024 report from the World Economic Forum and the McKinsey Health Institute found that women spend 25% more of their lives in poor health than men, even though they live longer [20]. It traces the gap to four root causes: science, data, care delivery and investment [21]. It also stresses that women’s health is more than sexual and reproductive health [21].

Less investment means less scientific understanding and less data, and that makes new investment look riskier [22]. In the US, the NIH spends about $5 billion a year on women’s health, roughly a tenth of its budget [6].

What is changing in 2026

On 28 and 29 September 2026, the European Medicines Agency held a dedicated workshop on women’s health in Amsterdam [5]. It produced 10 proposed priority actions, including better enrolment of women in clinical trials, high-quality reporting of data by sex and support for including pregnant and breastfeeding people [5]. EMA plans to publish a regulatory roadmap by the end of 2026 [5]. The EU Clinical Trials Regulation already requires that trial participants reflect the populations likely to use a medicine [23].

On 19 October 2026, a US executive order directed the NIH to create a Women’s Health Division within 90 days and set up a White House Women’s Health Task Force [6]. The division will work alongside the NIH’s existing Office of Research on Women’s Health, and the order sets no specific funding targets [24].

A roadmap and a new division set priorities. Whether they change who takes part in the next trials is not yet known.

What this means for taking part in research

Researchers have catalogued strategies to improve how many women join and stay in trials, which shows that participation is partly a design question [25]. Studies that fit around work and caring responsibilities are easier to take part in. At TrialMe, we explain how research works and help women explore studies that fit their health and their lives.

• What is the gender health gap?

  It is the difference between women and men in health outcomes, in the care they receive and in the evidence behind that care. Women live longer than men on average but spend 25% more of their lives in poor health [20].

• Why were women excluded from clinical trials?

  In 1977, after the thalidomide birth defects, the FDA recommended excluding women who could become pregnant from early drug trials to protect a possible fetus. The FDA reversed this in 1993 [1][2].

• Are women still under-represented in clinical trials?

  In many areas, yes. Women were 40.7% of participants in pivotal cancer drug trials but under-represented relative to disease burden in 66.9% of them [16]. In cardiovascular trials, the median participation-to-prevalence ratio was 0.77 [17].

• Do women respond differently to medicines?

  Often in ways that affect dose. In a 2020 analysis of 86 drugs, 76 produced higher exposure in women, and women had adverse reactions nearly twice as often as men [11]. Not every drug differs, and some differences run the other way [7].

• Is the gender health gap only about reproductive health?

  No. The World Economic Forum report stresses that women’s health is more than sexual and reproductive health [21].

• What is being done about it?

  In 2026, EMA proposed 10 priority actions and plans a roadmap by the end of the year [5]. A US executive order directed the NIH to create a Women’s Health Division [6].

Sources

1. US FDA, “Executive Summary: Gender Studies in Product Development” (archived). https://webarchive.library.unt.edu/eot2008/20090120110650/http:/www.fda.gov/womens/gender/Exec4.htm

2. Embryo Project Encyclopedia, “Guideline for the Study and Evaluation of Gender Differences in the Clinical Evaluation of Drugs.” https://embryo.asu.edu/taxonomy/term/144722

3. Westergaard D, et al. Population-wide analysis of differences in disease progression patterns in men and women. Nature Communications. 2019;10:666. https://doi.org/10.1038/s41467-019-08475-9

4. World Economic Forum, “Women’s health at Davos 2024” (citing McKinsey research). https://www.weforum.org/stories/equity-diversity-and-inclusion/women-health-davos-2024/

5. EMA, “Women are missing from medicines development: EMA’s roadmap for change,” 30 September 2026. https://www.ema.europa.eu/en/news/women-are-missing-medicines-development-emas-roadmap-change

6. Crowell & Moring, “Executive Order Creates Women’s Health Task Force, Rescinds Prior Initiatives.” https://www.crowell.com/en/insights/client-alerts/executive-order-creates-womens-health-task-force-rescinds-prior-initiatives

7. Applied Clinical Trials, “Sex and Race in Clinical Trials.” https://appliedclinicaltrialsonline.com/view/sex-and-race-clinical-trials

8. Beery AK. Inclusion of females does not increase variability in rodent research studies. Current Opinion in Behavioral Sciences. 2018. https://pmc.ncbi.nlm.nih.gov/articles/PMC6294461

9. FDA Drug Safety Communication, 10 January 2013 (copy). https://www.drugs.com/fda/zolpidem-containing-products-safety-communication-fda-requires-lower-recommended-doses-13303.html

10. Reuters via Bangor Daily News, “FDA recommends lower dose of insomnia drugs.” https://www.bangordailynews.com/2013/01/10/news/fda-recommends-lower-dose-of-insomnia-drugs-ambien-edluar-zolpimist/

11. Zucker I, Prendergast BJ. Sex differences in pharmacokinetics predict adverse drug reactions in women. Biology of Sex Differences. 2020;11:32. https://doi.org/10.1186/s13293-020-00308-5

12. Beery AK, Zucker I. Sex bias in neuroscience and biomedical research. Neuroscience & Biobehavioral Reviews. 2011;35(3):565-572. https://pubmed.ncbi.nlm.nih.gov/20620164/

13. Science News, “Biomedical studies are including more female subjects (finally).” https://www.sciencenews.org/article/biomedical-research-sex-male-female-animal-human-studies

14. “Considering Sex as a Biological Variable Will Be Valuable for Neuroscience Research.” Journal of Neuroscience. 2016;36(47):11817-11822. https://pmc.ncbi.nlm.nih.gov/articles/PMC5125240

15. Woitowich NC, Beery A, Woodruff T. A 10-year follow-up study of sex inclusion in the biological sciences. eLife. 2020. https://doi.org/10.7554/eLife.56344

16. Kalathoor S, et al. Representation of women in clinical trials supporting FDA approval of contemporary cancer therapies. International Journal of Cancer. 2024;155(11):1958-1968. https://doi.org/10.1002/ijc.35110

17. Consideration of sex/gender aspects in cardiovascular clinical trials. Clinical Research in Cardiology. 2025. https://doi.org/10.1007/s00392-025-02793-3

18. NICE, “New technologies could help cut years-long wait for endometriosis diagnosis” (copy). https://www.wired-gov.net/wg/news.nsf/articles/new+technologies+could+help+cut+yearslong+wait+for+endometriosis+diagnosis+07072026110500?open

19. Fryer J, Mason-Jones AJ, Woodward A. Understanding diagnostic delay for endometriosis: a scoping review. Health Care for Women International. 2024. https://ray.yorksj.ac.uk/id/eprint/10874/1/Understanding%20diagnostic%20delay%20for%20endometriosis%20%20A%20scoping%20review%20using%20the%20social-ecological%20framework.pdf

20. McKinsey Health Institute, “New report highlights $1 trillion potential of closing the women’s health gap,” 17 January 2024. https://www.mckinsey.com/mhi/media-center/new-report-highlights-one-trillion-potential-of-closing-womens-health-gap

21. World Economic Forum, “Closing the Women’s Health Gap: A $1 Trillion Opportunity.” https://www.weforum.org/publications/cerrar-la-brecha-en-la-salud-de-las-mujeres-una-oportunidad-de-1-billon-de-dolares-para-mejorar-vidas-y-economias-es

22. BioSpectrum India, summary of the WEF and McKinsey report. https://biospectrumindia.com/article/pdf/24090

23. EMA, “Women’s health.” https://www.ema.europa.eu/en/human-regulatory-overview/research-development/womens-health

24. AP via US News, “Trump signs an order aimed at boosting women’s health research.” https://www.usnews.com/news/health-news/articles/2026-10-19/trump-will-sign-an-order-aimed-at-boosting-womens-health-research-a-plan-backed-by-the-first-lady

25. Strategies for enhancing the representation of women in clinical trials: an evidence map. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC10759390/