The purpose of clinical research is to understand how the human body works and to apply that knowledge to improve health outcomes. For clinical research to be truly useful, it must reflect the populations that it intends to help. Women and men have different hormones, different organs, and different cultural influences—all of which can lead to differences in health. If research findings are to be used to inform women’s treatment, then women must be included as research participants.

Including women in clinical studies isn’t just the right thing to do scientifically; it’s also the law. NIH is required to ensure that women and minorities are included in all clinical research as appropriate to the scientific question under study and that Phase III clinical trials be designed to assess any differences in an intervention’s effects by sex and race/ethnicity. These laws are reflected in the guidelines and policies that NIH has created for NIH research grants, cooperative agreements, and contracts.

A range of factors can affect people’s ability and motivation to participate in a clinical study, including whether the prospective participants already have access to treatment in their community, potential risks associated with the study, and whether participation is convenient. Understanding and addressing the barriers for a particular study population can help researchers improve recruitment and retention.