For decades, medicines were tested largely on men, even though women’s bodies can respond differently to symptoms, treatments and side effects. It wasn’t until the 1990s that women began to be properly included in clinical trials, changing the future of healthcare and medical research.
Clinical trials have existed for centuries and remain one of the most important ways to understand whether a treatment is safe and effective. But for much of modern medical history, women were either underrepresented or excluded entirely from research studies.
One of the biggest turning points came after the thalidomide tragedy in the 1960s, when a drug prescribed during pregnancy caused severe birth defects in thousands of babies worldwide. The fear surrounding drug safety and pregnancy led the US Food and Drug Administration (FDA) in 1977 to recommend excluding women of childbearing age from early-stage clinical trials.
While the decision aimed to protect women and unborn children, it also created a major gap in medicine. For nearly a decade, many pre-menopausal women were excluded from research, meaning scientists had limited data on how medicines affected female bodies.
The consequences were serious. Women were left out of trials for important medications, including some HIV treatments during the AIDS crisis of the 1980s. At the time, growing protests and criticism highlighted how women’s health was being overlooked.
Things slowly began to shift in the late 1980s and early 1990s. The National Institutes of Health (NIH) started encouraging researchers to include women in studies, and in 1993, inclusion policies were officially written into federal law. Researchers were now required to include women and minority groups in clinical trials.
The impact has been significant. Studies focusing on women’s cardiovascular health, breast cancer and cervical cancer have improved diagnosis, treatment and awareness. Researchers also discovered that women may experience diseases differently from men, including differences in symptoms, drug responses and side effects.
Statistics show progress, but also reveal the gaps that remain:
- Around 30% of participants in early-stage industry-sponsored trials are women.
- A 2001 review found women made up 56% of participants in phase 2 and 3 trials.
- Yet, in a 2021 review of over 4,400 COVID-19 clinical trials, only 4% analysed results by sex.
This matters because women are not simply “smaller men” medically. Hormones, metabolism, body composition and reproductive health can all influence how treatments work.
There is also growing evidence that having more women leading research changes outcomes. A 2023 analysis found that clinical trials with female lead authors enrolled more women participants than those led entirely by men.
Today, conversations around equitable healthcare continue to evolve, but experts say more representation is still needed, not just in participation, but in leadership, analysis and funding priorities.
As awareness around women’s health grows globally, clinical trials are increasingly being viewed not only as scientific research, but as a matter of healthcare equality.