“When I see a patient in the NIH Clinical Center hospital, I know that she—or he—has an expectation that the care I give is the most appropriate for a female or a male body. As a clinician, I am only able to do that to the extent that biomedical research has provided the tools and the knowledge.”—Janine Austin Clayton, M.D., FARVO, NIH Associate Director for Research on Women’s Health

Sex and gender can influence health in important ways. While sex and gender are distinct concepts, their influence is often inextricably linked. The scientific studies that generate the most complete data consider sex and/or gender influences in study design, data collection and analysis, and reporting of findings. 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.

There are obvious differences between men and women, such as those related to reproduction, but these obvious differences are only one portion of the human body. Sex differences go far beyond the reproductive system. We know that certain health conditions are more common in women than in men, such as osteoporosis, depression, and autoimmune diseases.1,2,3 There are also many diseases that affect women and men differently, such as heart disease.4 A woman experiencing a heart attack may have pain in her shoulder and her jaw, while a man may present with chest pain and shortness of breath. Women and men may also respond to medications in different ways.5 A woman may need a lower dose or different treatment regimen. For example, we know that low-dose aspirin has different preventive effects in women and men and that drugs such as zolpidem, used to treat insomnia, require different dosing in women and men. To capture these important phenomena, clinical research must include both men and women.

For these and many other reasons, including women in clinical research makes results stronger and more robust. Including women in clinical research also makes it possible for scientists to draw conclusions that advance health for both women and men. Enrolling women in a research study along with men could help in understanding the mechanism by which a treatment works and help identify people likely or unlikely to be helped by the protocol.

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, and this website will help you think through how the inclusion of women6 supports strong study design.

  1. National Institutes of Health, National Institute of Arthritis and Musculoskeletal and Skin Diseases. (2015, June). Osteoporosis in men. Retrieved from
  2. Nemeth, C. L., Harrell, C. S., Beck, K. D., & Neigh, G. N. (2013). Not all depression is created equal: sex interacts with disease to precipitate depression. Biology of Sex Differences, 4, 8. Retrieved from
  3. Ngo, S. T., Steyn, F. J., & McCombe, P. A. (2014, August). Gender differences in autoimmune disease. Frontiers in Neuroendocrinology, 35(3), 347–369. doi:10.1016/j.yfrne.2014.04.004. Retrieved from
  4. American Heart Association. (2015, July). Heart attack symptoms in women. Retrieved from
  5. National Institutes of Health, National Heart, Lung, and Blood Institute. (2005, March 7). Statement from Elizabeth G. Nabel, M.D., Director of the National Heart, Lung, and Blood Institute of the National Institutes of Health on the Findings of the Women's Health Study. Retrieved from
  6. Attention to these topics in the design of a research project will assist in the appropriate inclusion of women in studies.The term “inclusion of women” refers to the legal requirement set forth in the National Institutes of Health Revitalization Act of 1993 that women must be included as subjects in clinical research. This requirement pertains to all clinical research funded by NIH unless the research “is inappropriate with respect to the health of the subjects,” “is inappropriate with respect to the purpose of the research,” or “is inappropriate under such other circumstances as the Director of NIH may designate.”