Why Women Belong in Clinical Research

Every time you take a supplement, use a skincare product, or are prescribed a medication, you are trusting that it was tested properly.

But for decades, “proper testing” didn’t include testing on women.

Despite making up half the global population, women were historically underrepresented in much of modern clinical research, particularly in early-phase drug trials. This has been the case in clinical research studies, even when diseases affect them equally or more frequently than men.

The History of Women in Clinical Research

For much of the 20th century, the “default patient” in medicine was male.

In 1977, the U.S. Food and Drug Administration (FDA) recommended excluding women of childbearing potential from early-phase drug trials following tragedies such as thalidomide-related birth defects. The pattern y wasn’t just a U.S. issue. Underrepresentation of women in clinical research has historically been a global problem. While intended as protection, the policy resulted in the widespread exclusion of women from research.^[1]

It wasn’t until 1993, with the passage of the NIH Revitalization Act, that U.S. law required NIH-funded clinical trials to include women and minorities, and to analyze outcomes by sex.

Are Women Included in Clinical Research?

Yes, but significant gaps still remain.

Even today:

• Women are underrepresented in many cardiovascular^[2], oncology, and neurology trials relative to disease prevalence.^[3]
• Pre-menopausal women are sometimes avoided because hormonal cycles are viewed as “complicating variables.”^[4]
• Pregnant and nursing women are routinely excluded, leaving major knowledge gaps in medication safety during these time periods.
• Even in preclinical research, male animals are still disproportionately used because female hormonal cycles are perceived as adding “variability.”^[5]

Ironically, what researchers once considered “complexity” is precisely why inclusion is essential.

Why Is It Important for Women to Be Included in Clinical Trials?

Men and women are biologically different in many ways, and present disease uniquely. That may sound obvious, but for decades, medicine operated as if we were the same.

Drug metabolism is different

Women have unique hormone dynamics and organ function, all of which can and do change how a drug interacts. As a result, women experience adverse drug reactions more frequently than men, with some analyses suggesting rates up to twice as high.^[6]

The landmark review by Zucker and Prendergast found that for most of the FDA-approved drugs they examined, women had elevated blood concentrations and longer elimination times compared to men, and this “risks overmedication of women, and contributes to female-biased adverse drug reactions.”^[7]

Disease presents differently

Take cardiovascular disease, the number one killer of women worldwide.

It was long called a “man’s disease,” but the risk in post-menopausal women is just as high. Because women were understudied, symptoms in women may be misrecognized.^[8]

The result is slower diagnoses and less precise care.

What Are The Consequences of Excluding Women From Clinical Trials?

The practical consequences of excluding women have been stark. Drugs approved before 1993 often had little to no female safety data.

When women are not adequately studied, real-world consequences follow.

• Inadequate dosing: The widespread finding that women suffer adverse drug reactions at up to twice the rate of men traces back to this imbalance.
• Ineffective care: Treatments developed mostly in men may work poorly or unpredictably in women. For example, clinical guidelines for heart attacks and depression sometimes grew out of studies with few women, leading to misdiagnoses in women.
• Safety risks: Not studying women means unknown dangers for women. For instance, pregnant women on common medications lack evidence-based safety or dosing information.

How Is Women’s Research Changing?

Women now make up almost half of the participants in NIH-supported studies.^[9] The NIH also now requires researchers to consider sex as a biological variable in both clinical and preclinical research, shifting the focus from simple inclusion to meaningful analysis.

Regulatory agencies are also evolving. The FDA’s Office of Women’s Health encourages sex-specific data analysis and dosing recommendations that are informed by the pharmacokinetic differences between men and women. In some cases, labeling changes have been made where women were found to metabolize drugs differently from men.

While more women are now being represented in clinical research, major gaps still exist, particularly for pregnancy and lactation, and during perimenopause and menopause.

But inclusion alone is not enough.

True equity in research requires more than enrolling women. It requires analyzing outcomes by sex, reporting those findings transparently, and designing studies that account for life stages such as pregnancy, perimenopause, and menopause. It also requires studying diverse populations across age, race, and ethnicity to ensure findings reflect real-world biology.

Timeline’s Inclusive Clinical Research

Timeline aims to change the norm. We design all our studies to be inclusive of women and other underrepresented groups. In fact, across 25 Mitopure trials, we have enrolled 2,200+ participants, of whom about two-thirds are women.

Our volunteers range in age from 18 to 89, from athletes to elderly participants, with women being well represented. By studying diverse populations, we ensure our findings apply to all.

For example:

• 500 mg of Mitopure increases muscle strength by 12%. 60% of the study participants were women.*^[10]
• 1000 mgs of Mitopure was shown to increase muscle endurance in older adults. 70% of the study participants were women.†^[11]

Women Scientists Leading the Way

In addition to including women in trials, Timeline elevates women in research roles. Our in-house science team includes leading experts such as Dr. Julie Faitg, PhD, and Andréane Mégane Fouassier, both world-class mitochondrial researchers.

We take pride in having such accomplished women scientists on our team. Their leadership ensures that women’s perspectives shape our research, and it inspires more women to participate in science.

†Our clinical studies showed that sedentary adults aged 65–90 improved muscle endurance, measured as leg repetitions to fatigue, after daily supplementation with 1,000 mg Mitopure®.