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Why are women and people with cycles underrepresented in health research?

How can medical science better serve women and people with cycles?

by Ijeoma Unachukwu, M.S., and Magdalena Geretto, MD, MSc Medically reviewed by Rachel Mason, MD
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Top things to know

  • Women and people with cycles have been historically excluded from medical research

  • This compromised the quality of healthcare that was available to women and people with cycles

  • Efforts have been made to include women and people with cycles in health research, but due to historical underrepresentation, we now know far less about how diseases affect women and people with cycles in comparison to men.

The exclusion of women and people with cycles from research studies has led to a dearth of information about their health. This exclusion has been a result of historical, cultural, and systemic forces that stigmatize women’s participation in scientific processes.

Luckily, things are changing. In the past few decades, there has been a momentous shift in attitudes and requirements for who should be included in clinical studies, positively influencing research for the benefit of women, people with cycles, and other historically marginalized groups (1).


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Why have women and people with cycles been excluded from health research?

In the first half of the 20th century, there was limited regulation in research. From the 1940s to the 1970s, the drugs thalidomide and diethylstilbestrol were prescribed to women for various ailments. Unfortunately, the negative effects of these medications on the babies of pregnant women had not been explored before their approval for public use (2,3,4). Tragically, thousands of women who took thalidomide while pregnant gave birth to babies with severe limb deformities (4,5). In response, countries worldwide began more strictly regulating the way medications are studied, approved, prescribed, and marketed, in order to better protect the public (6). This also meant that, in the USA, researchers excluded all women of reproductive age from early-stage drug testing, in an effort to avoid negatively affecting their fertility (7). In the following decades, the majority of clinical trials used data that primarily came from studies involving white men (8). 

Since women weren’t represented in important medical research, the quality of healthcare that was available to them was compromised (9). There were some exceptions, including studies on the efficacy of hormonal birth control in the 1970s and the 1980s, some of which were led by female scientists (10). However, research on health issues that affect all sexes, like hypertension and diabetes, predominantly used men as subjects. As a result, men became perceived as the “gold standard” of research subjects by scientists (11), with the false belief that women’s bodies would always behave similarly to men’s bodies in clinical trials (8). Additionally, some scientists believed women’s bodies were too complex and too expensive to study (8). Including women in research would mean that scientists would have to account for factors like the menstrual cycle and the possibility of pregnancy. Instead, scientists of the period chose to ignore these key differences.

Public concern over a lack of data on how drugs affect women and the belief that women should be able to choose whether to participate in research spurred growing activism on behalf of inclusive research. In the USA, the Women’s Health Movement encouraged women to advocate for their health and eventually influenced the development of a federal Task Force on Women’s Health Issues in 1983, which recommended that more research be done in the area of women’s health (12). And in 1993, the National Institutes of Health mandated that any clinical research study that received federal funding include women and minorities (13). In Canada, rising concerns about a deficit of research on breast cancer and gynecological cancers led to the development of the “Canadian Guidance Document on the Inclusion of Women in Clinical Trials” (14), which recommends the inclusion of women in all stages of research, so that scientists can understand the impact of new drugs on specific sexes (14).

By the early 2010s, women accounted for 45% of subjects in middle- and late-stage trials of new drugs in the USA (15). However, female inclusion still varies widely, depending on the field of research. Women still remain underrepresented in research on heart disease and cancer, diseases that are the leading causes of death for women (16). In Europe, clinical trials used to focus mainly on men until the 1990s (17). However, things changed when the European Union passed a law requiring researchers to identify differences between men and women in clinical trials (18). Later, in 2016, the European Union introduced a new regulation stating that clinical trials must include the populations who are likely to use the medical product being tested (19). It is not just the European Union addressing the issue of gender bias in clinical research, but also national bodies. The Ethical Committee of the Medical University of Vienna released guidelines that recommend that both biological sexes should be included in medical and behavioral research (20).

A study in 2019 found that women, and especially women who are pregnant and elderly, continue to be underrepresented in clinical trials (14). There has been a recent debate about the inclusion of pregnant and lactating people in clinical research (21). Many scientists and stakeholders involved in the process think that it is important to include these groups to better understand their needs, improve their healthcare, and provide safe and evidence-based therapies (22). They believe those groups should not be regarded as "vulnerable" and automatically excluded from research (23). Instead, they must be viewed as "medically complex" and ways need to be explored to actively involve them in medical research (24). In 2016, the European Union published regulations for including pregnant and lactating people in clinical research, that set out how to include these groups in research while ensuring their safety (25).

It is important to note, that even when women or people with cycles are included in clinical trials, researchers still frequently fail to analyze and report on sex-specific differences. Such practice makes it difficult to understand how sex can influence health and disease (26). It is generally accepted that a person’s biological sex can affect how well a drug works. The side effects they experience may also differ. Ignoring these differences when conducting medical research or clinical trials can result in incorrect or incomplete conclusions about how effective or safe a drug can be (27). 

Why is it important to include women and people with cycles in research? 

The fact that women and people with cycles have been underrepresented in health research means that we now know far less about how diseases affect women and people with cycles, in comparison to men, which can lead to dangerous consequences (28).

Though heart disease is the leading cause of death among men and women, a majority of research about heart disease has been conducted on men (8,29). As a result, past research has missed out on key differences between sexes, when it comes to heart disease. Women, for instance, have more incidents of heart disease than previously thought, and they die from heart disease more frequently than men (29,30). Research has also missed key differences in how heart attacks present in women: while both men and women experience chest pain, women are more likely to report pain radiating to the back, neck, or jaw, as well as left arm pain (31). Failing to understand the symptoms of a heart attack in women and people with cycles puts them at risk of being misdiagnosed or treated incorrectly. 

Another area of interest is autoimmune diseases, where biological sex differences play a crucial role (32). The development of autoimmune diseases is significantly influenced by biological sex. Therefore, sex should always be taken into account in studies aimed at understanding autoimmune diseases (33).

Sex bias in research has also affected drug research and development. For decades, healthcare guidelines and standards did not differentiate between sexes and did not address how drugs affected female bodies (9,34,35), though there are distinct physiological and anatomical distinctions between the sexes, like differences in body mass, organ function, and hormone levels (36). A female person and a male person can be prescribed the same dose of a drug, but differences in body composition and body function may lead to different effects in different bodies (36,37,38). 

Sex disparities in research also lead to a lack of resources and information about women’s health. Inadequate health literacy is linked to poor health outcomes and higher mortality (39).  Sexual and reproductive health education is a necessary component to improve the lives of women and people with cycles. For instance, we know that reproductive health literacy leads to the reduction of STIs, unintended pregnancies, and maternal mortality (40,41). 

Toward a more inclusive future

Research that is inclusive of women and people with cycles has come a long way since the 20th century. According to data from the FDA, the representation of women in clinical trials has been increasing over the years (42). These figures show that we are on the right track towards inclusion. What still needs to be improved is the inclusion of women of color and people of color more generally, as they remain underrepresented in clinical research (28). In recent years, there has been an uptick in advocacy and research in regard to women and people with cycles. Historic organizations like the Women’s Health Initiative and the National Women’s Health Network continue to fight for the right for women and people with cycles to have access to menstrual products, birth control, health screenings, and health information.

Clue is using data to advance women's health research. Our science team is helping to answer questions like: How does contraception impact sex drive or breast tenderness patterns? Does air pollution influence cycle length variability? How do exercise and stress impact teens’ menstrual cycles? You can read about all of Clue’s scientific partnerships here. The work we do alongside our partners helps to close the gender health gap and improve the health outcomes and life quality of women and people with cycles. 

Tracking your cycle with Clue not only supports our research activities and goals, but also helps every user to better understand their bodies, take charge of their reproductive health, close the diagnosis gap, and live in sync with their cycles. Download Clue to start tracking. 

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