Women are poorly represented in clinical trials. That’s problematic

Clinical research is the foundation of modern medicine, shaping the safety and efficacy of drugs. But for decades women — particularly those of childbearing potential — are routinely excluded from clinical trials.

Fewer than 30% of participants in industry-sponsored early-phase trials are women¹, an exclusion shaped by fears of legal liability, and perpetuated by a medical culture that assumes men’s bodies are the default for drug testing. The roots of this bias trace back to 1962, when the thalidomide tragedy led to a blanket ban by the Food and Drug Administration (FDA) in 1977 on including women of childbearing age in early-phase clinical trials². The intent was protection; the effect was systematic neglect. Even after the ban was lifted in 1993, the legacy of exclusion remained entrenched³. Today, pharmaceutical companies and clinicians continue to sideline women in trials, citing concerns about pregnancy risks and hormonal fluctuations.

But this omission carries serious consequences. Medicine has long treated women as ‘smaller men’ assuming that drugs tested on male bodies would work the same way in females. Science says otherwise. Women have distinct hormonal cycles, metabolic rates, immune responses, and fat distribution, all of which affect how they absorb, process, and respond to medications. Studies have found that 76 out of 86 commonly used drugs exhibit sex-based pharmacokinetic differences, yet dosing guidelines often fail to account for this. The result? Women experience adverse drug reactions at nearly twice the rate of men⁴.

COVID-19 provided a stark example of this bias. Despite clear evidence that men and women had different infection rates, drug responses, and mortality risks, only 4% of clinical trials actively sought to recruit women. The data gap is particularly glaring in pregnant and lactating women. Most drug labels carry the disclaimer: “Safety in pregnancy not established.” This leaves expectant mothers with an impossible choice: risk taking an untested drug or forgo treatment entirely⁵.

So, why does this continue? Part of the problem lies in the pipeline of clinical research itself. Men dominate leadership roles in biomedical research, and the percentage of female principal investigators is far below parity. When women aren’t designing studies, their exclusion becomes self-perpetuating. Financial factors also play a role — preclinical research often avoids including female animals due to perceived cost burdens and ‘complicating’ hormonal cycles⁶.

Even when women are included in trials, systemic barriers persist. Caregiving responsibilities make participation difficult. Many studies require women of childbearing age to use long-acting contraceptives, an additional hurdle given cultural and financial barriers to access.

Recent AI-driven analyses of 50 years of FDA reports have identified sex-based disparities in drug side effects. Such tools should be actively integrated into trial planning to preemptively address gender biases in research⁷.

Failing to close this gap isn’t just unfair, it’s dangerous. As we brace for future pandemics and medical challenges, continuing to treat women as afterthoughts in medicine is a crisis waiting to happen. The world cannot afford to ignore half its population.

Participation of women in clinical research isn’t a privilege. It’s a right.