Clinical trials are crucial for advancing medical knowledge, developing life-saving treatments, and improving healthcare outcomes. However, for much of history, the participation of women in clinical trials has been limited or non-existent. In this blog, we explore the history of women's inclusion in clinical trials, highlighting the challenges faced and the progress made over time.

Early exclusion

In the early days of clinical trials, women were often excluded due to societal norms and misconceptions about their physiological differences. Clinical research predominantly focused on men, assuming that their bodies were representative of the entire population. As a result, many medical interventions, drugs, and treatments were developed without considering potential sex-specific differences.

The thalidomide tragedy

A pivotal event that shed light on the importance of including women in clinical trials was the Thalidomide tragedy of the 1950s and 1960s. During this time, Thalidomide, a sedative and anti-nausea drug, gained widespread availability. It was marketed by 14 pharmaceutical companies across 46 countries, using at least 37 unique trade names. It was frequently prescribed to pregnant women as a treatment for morning sickness.

Unfortunately, the drug had not been tested on pregnant women and researchers were unaware that the drug could pass through the placental barrier and harm a foetus. Congenital defects included issues with limbs, internal organs including the brain, hearing, and eyesight – and because of the wide range of these defects, it took five years to determine that thalidomide was the cause.

Thalidomide caused significant harm, impacting over 10,000 infants globally. Tragically, approximately half of them passed away shortly after birth. The surviving babies, along with their families, continue to face the long-lasting consequences of the drug. This devastating incident highlighted the need for more comprehensive and inclusive clinical trials that considered the unique physiological aspects of women and took pregnancy into account.

The push for inclusion

In response to the thalidomide tragedy, which exposed the potential consequences of insufficient research and exclusion of women from clinical trials, regulatory agencies and advocacy groups embarked on a mission to change drug development and strengthen regulatory authorities. 

In 1975, the US National Commission for the Protection of Human Subjects and Biomedical and Behavioral Research named pregnant women as vulnerable research subjects, and two years later women of childbearing age were banned from early phase clinical research in the US, with an exception for life threatening conditions.

This was not reversed until 1993, when the National Institutes of Health (NIH) Revitalization Act mandated adequate inclusion of women and minorities in NIH-sponsored clinical trials. This act aimed to address historical disparities and promote more inclusive and representative clinical trials. Five years later, the FDA began requiring safety and efficacy data by sex. Similar changes were set in motion in the United Kingdom and across Europe, as regulatory bodies in these regions also recognized the imperative of including women in clinical trials. 

Research began to highlight the differences between men and women in terms of drug metabolism, side effects, and treatment responses. For example, studies showed that women may require different dosages or experience different side effects compared to men. This understanding further emphasised the importance of women's inclusion in clinical trials.

Looking to the future

While progress has been made, challenges persist in achieving full sex equality in clinical trials. Women continue to face barriers due to factors such as pregnancy, hormonal fluctuations, and the potential impact on foetal development. Understandably, concerns about liability and ethical considerations can also lead to hesitancy in including pregnant women in trials.

Efforts are underway to address the remaining challenges and ensure greater representation across the board in clinical trials. The FDA continues to refine its guidelines to encourage sex, race, and ethnic diversity and improve the understanding of differences in drug response. Additionally, initiatives such as the Women in Clinical Trials campaign raise awareness about the importance of women's inclusion and advocate for their active participation.


The history of women in clinical trials reflects a journey from exclusion to inclusion, driven by tragedies, regulatory changes, and evolving scientific knowledge. While significant progress has been made, there is still work to be done to ensure equity and equality in clinical research. By embracing broad diversity in clinical trials – with all sexes, races, and ethnicities appropriately represented, we can pave the way for better healthcare outcomes for all.

To learn more about the work Sano is doing to drive diversity in clinical research, get in touch below.

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