.png)
The Gaps · Science
The Science Gap
What’s actually known about sex-based biological differences is a live, moving line, not a fixed body of knowledge. Too little research funding goes toward finding these differences in the first place, and even when a study includes both sexes, most don’t report results broken out by sex, so a real difference can hide inside an average.
what the effect is
A 2026 Northwestern University analysis of 574 papers from NIH-funded grants (published 2017 to 2024) found that while 61% of studies included both sexes, only 44% of those analyzed their results by sex, and 17% didn’t report how many women and men they enrolled. Human studies did better than animal studies. Who does the science matters too: papers with a woman as first author analyzed by sex 50% of the time, versus 39% with a man as first author, and teams with women as both first and last author were more than twice as likely to do so.
​
What that costs women shows up in the medicine cabinet. Across 86 FDA-approved drugs, 76 had higher pharmacokinetic values in women, meaning the same dose produces higher drug concentrations and slower clearance. Of the drugs with female-biased pharmacokinetics, 96% were associated with a higher incidence of adverse drug reactions in women than in men. Earlier, the GAO found that 8 of the 10 prescription drugs withdrawn from the US market between 1997 and 2000 posed greater health risks for women than for men. In 2013, the FDA cut the recommended dose of the sleep drug zolpidem for women in half, because women clear it more slowly.
​
Source: Warden et al. (Northwestern University), Communications Medicine, 2026; Zucker and Prendergast, Biology of Sex Differences, 2020; US GAO, GAO-01-286R, 2001; FDA, zolpidem dosing, 2013.
​
​
What's still missing
Permission to include is not a requirement to include, or to analyze. The 1993 Act opened NIH-funded trials to women and sex as a biological variable has been NIH policy for over a decade, yet a study can satisfy both, enroll few women, and never break its results out by sex. The honest obstacle is cost: a sex-disaggregated result needs each group powered on its own, so it raises enrollment, sites, and budget. That makes it a question of who funds the larger trial, not of scientific difficulty. Nature requires the reporting for submitted research and remains close to alone among journals in doing so.
​
Trials designed so women can take part. Two obstacles recur. Cycling hormones are expected to widen the spread of results, and the honest answer is that characterizing that variation is a large part of why the data is needed, since a treatment women take across a cycle should be understood across one. The second is practical, since carrying more of the caregiving at home makes repeated travel to a site harder. That constraint is easing: the FDA’s 2024 guidance on decentralized elements allows telehealth visits, local providers, and remote data collection, and its 2023 guidance on digital health technologies makes home onboarding and validated wearables a workable design.
​
The lab bench, where the evidence base starts. Across ten biological disciplines, single-sex studies showed male bias in eight, and only 28% of recent NIH-funded animal studies analyzed results by sex. The usual reason given, that estrous cycling in female animals adds variability, has been tested: across 142 traits in more than 50 rat strains, variability was similar between the sexes, and 59% of the traits that did differ were more variable in males (Hypertension, 2016). Cells often go unnamed by sex at all, with half of 107 papers in one physiology journal’s 2018 volume omitting it.
​
Pregnancy, lactation, and an institutional owner. Roughly 70% of pregnant people take a prescription medication while still being excluded from most studies, which the National Academies has now flagged twice, in 2022 and 2024. Endometriosis and PMOS, meanwhile, sit inside no single NIH Institute, so no one is accountable for prioritizing them.
​
The money, and what kind of money it is. Two large figures circulate and both are requests rather than budgets. The National Academies asks Congress for $15.7B over five years, aimed at NIH, and the National Strategy to Close the Women’s Health Gap, launched in July 2026 by ACOG, SWHR and the Women First Research Coalition with more than 30 organizations behind it, asks for $20B over a decade across research, workforce, data infrastructure, regulation, and public education. Neither has been appropriated, and no dedicated women’s health institute exists. What is real is the base: NIH funded at $48.7B under its current structure, and the Women’s Health Initiative restored in May 2025, both covered below.
How the Compendium fits.
The reporting gap above, studies that include both sexes but never break results out by sex, means real findings on sex-based differences already exist scattered across the literature, just not surfaced or connected anywhere. That’s a direct match for what the Compendium does: it doesn’t generate new science, it catalogs what’s already been found, including results buried in a paper’s supplementary tables rather than its headline conclusion, and flags when something changes what’s known.
Janusmed shows this is possible at the scale of one country’s prescribing guidance, and GenderMedDB showed in 2014 that the literature can be compiled this way before that project went dark. The Compendium is built to do it at the scale the National Academies report says the field actually needs, reviewed monthly rather than compiled once and left to age, which is the part that makes it durable.
where the gap starts
For most of modern medicine, women were treated as “little men”: assumed to be the same as men at the cellular level, different only in reproductive organs and body size, with doses scaled down to fit. In 2001, the Institute of Medicine concluded the opposite: every cell has a sex.
By then the assumption was built into drug development. From 1977 to 1993, FDA guidance recommended keeping women of childbearing potential out of early-phase drug trials, and in practice that shut out nearly all premenopausal women, including those on birth control or abstaining from sex.
​
Source: Institute of Medicine, Exploring the Biological Contributions to Human Health: Does Sex Matter?, 2001; NIH Office of Research on Women’s Health, History of Women’s Participation in Clinical Research; AAMC, Why We Know So Little About Women’s Health; Merkatz et al., New England Journal of Medicine, 1993.
why this is a gap
Leaving women out was framed as the simpler, cheaper choice. Cycling hormones were expected to make results more variable, so studies would need more participants and more money, and findings in men were assumed to carry over to women.
That reasoning has been tested and has not held up: across hundreds of rodent studies, females were no more variable than males. But the research base had already been built on males. The 1993 NIH Revitalization Act brought women into NIH-funded trials, and NIH has expected sex to be treated as a biological variable since 2016, yet being included still isn’t the same as being analyzed.
​
Sources: AAMC, Why We Know So Little About Women’s Health; Beery and Zucker, Neuroscience & Biobehavioral Reviews, 2011; Prendergast et al., Neuroscience & Biobehavioral Reviews, 2014; Becker et al., Biology of Sex Differences, 2016; NIH Revitalization Act of 1993; NIH, NOT-OD-15-102, 2015.