In 2016, the National Institutes of Health implemented a policy requiring researchers applying for NIH funding to account for sex as a biological variable (SABV) in the design, analysis, and reporting of preclinical research. It was not a radical step. It was a correction to decades of research practice that had systematically underrepresented female cells, tissues, and animals in basic science — and then applied findings to women as though the gap did not exist.
That policy is now under pressure. Amid broader scrutiny of NIH diversity and equity initiatives, the future of the SABV requirement is uncertain. Understanding what is at stake requires understanding what the policy actually does — and what omitting sex from preclinical research has historically produced.
Why Preclinical Sex Differences Matter
Drug metabolism, immune response, pain sensitivity, and cardiovascular risk all differ by sex at the biological level. These are not sociological observations — they are measurable physiological differences with direct clinical implications. When a drug is tested exclusively or predominantly in male animal models, the resulting data on efficacy and side effects may not generalize to female patients.
This is not a theoretical concern. It has produced documented harms. Several drugs approved based on predominantly male trial data were later found to cause higher rates of adverse effects in women. Zolpidem (Ambien) is a well-known example: the FDA reduced the recommended dose for women in 2013 after post-approval data showed women metabolized the drug more slowly, resulting in morning impairment at the originally approved dose.
What the SABV Policy Has Achieved
In the decade since the policy was implemented, researchers have begun to report sex-disaggregated data with greater consistency. Studies have identified sex differences in disease mechanisms that were previously uncharacterized. The research infrastructure — including the methods, training, and reporting standards — has developed in ways that would be difficult and costly to reverse.
The policy has not been without implementation challenges. Some researchers have found the requirement burdensome. Others have questioned whether it is always scientifically appropriate to include both sexes in every preclinical model. These are legitimate methodological conversations. They are different from the question of whether sex should be considered at all.
The Rollback Risk
Reports emerging from NIH in early 2026 suggest that SABV requirements may be weakened or de-emphasized as part of broader changes to the agency’s research priority framework. If accurate, this would represent a significant regression.
The women’s health research community has been clear about the stakes. The Society for Women’s Health Research, which has advocated for sex differences research for more than three decades, has consistently argued that the SABV policy is not a diversity initiative — it is a scientific quality standard. Eliminating it does not produce neutral science. It produces science that is systematically less accurate for half the population.
What Comes Next
Congressional oversight of NIH research priorities is intensifying. Several members of Congress with records of supporting women’s health research have raised concerns about the direction of the agency under its current leadership. Whether those concerns translate into legislative action or meaningful oversight hearings remains to be seen.
What is clear is that the SABV policy — and the scientific principle underlying it — will require active defense. The progress made over the last decade is real. It is also reversible.
