Women and men have different hormones, different organs, and different cultural influences — all of which can lead to differences in health. The purpose of clinical research is to understand how the human body works and apply that knowledge to improve health outcomes. For clinical research to be truly useful, it must reflect the populations that it intends to help.

Including women in research is not just a matter of enrolling women in clinical studies. It also requires consideration of how research is designed, a process that occurs long before volunteers sign up for a study. When planning, designing, and conducting clinical research, it is imperative to consider both sexes.

ORWH helps the research community understand that including women in clinical research makes results stronger and more robust and makes it possible for scientists to draw conclusions that advance health for both women and men.


The establishment and implementation of policies for the inclusion of women and minorities in clinical research funded by NIH has its origins in the women's health movement. Following the issuance of the report of the Public Health Service Task Force on Women's Health in 1985, the NIH established a policy in 1986 for the inclusion of women in clinical research. In order to ensure that the policies for inclusion were firmly implemented by NIH, the Congress made what had previously been policy into Public Law, through a section in the NIH Revitalization Act of 1993 (PL 103-43), entitled Women and Minorities as Subjects in Clinical Research.

In 2001, the NIH Policy and Guidelines on the Inclusion of Women and Minorities as Subjects in Clinical Research were updated and incorporated the definition of clinical research as reported in the 1997 Report of the NIH Director's Panel on Clinical research. The guidelines also incorporated the Office of Management and Budget (OMB) Directive's 15 racial and ethnic categories to be used when reporting population data. The 2001 policy also provides additional guidance on reporting analyses of sex/gender and racial/ethnic differences in intervention effects for NIH-defined Phase III clinical trials.

Related to sex-specific reporting, but distinct from inclusion, NIH announced in 2014 a new policy requiring that preclinical research consider sex as an important biological variable (Clayton and Collins 2014) in both vertebrate animal and human studies. Under the new policy, in effect as of January 2016, applicants would be asked to "explain how relevant biological variables, such as sex, are factored into research designs and analyses." Strong justification from the scientific literature, preliminary data, or other relevant consideration is required from researchers planning to study only one sex. The absence of evidence about differences between males and females in previously published research could not serve as a justification for as single sex study. (See Consideration of Sex as a Biological Variable in NIH-funded Research, companion reference to NIH Guide Notice NOT-OD-15-102  (PDF - 74.6KB)).

The policy was introduced because there is growing recognition that the quality and generalizability of biomedical research across the research continuum depends on appropriate consideration of key biological variables, such as sex. Women now account for roughly half of all participants in NIH-supported clinical research. However, many preclinical research studies continue to rely heavily on male animals and/or omit reporting of the sex of animal subjects. This is particularly problematic in studies intended to inform understanding of diseases and conditions affecting both sexes. Failure to account for sex as a biological variable may undermine the rigor, transparency, and generalizability of research findings. Under the new policy, researchers are expected to study both male and female vertebrate animals and human subjects (including clinical research), where applicable, thereby improving our understanding of health and disease in men and women. The new policy serves as a complement to the inclusion policy, expanding consideration of sex in research designs, analyses, and reporting across the research continuum, from preclinical studies to clinical interventions.