Women are often excluded from clinical trials because periods

When your doctor prescribes you a common medication you expect it to be safe, right? After all, the drug underwent rigorous testing and numerous clinical trials before making it to market. This may be true, but a new paper points out that too many of these trials fail to include WOMEN. So really, doctors have very little idea how many drugs interact with the female body.

Why do researchers fail to include women, you ask? Well, taking the time to specifically test drugs on women is, like, hard, since women have periods and menopause and stuff.

Thankfully, a growing number of scientists are fed up with this gender testing gap and demanding change. In a new paper published in the journal Cell Metabolism, researchers from hospitals including Cedars-Sinai Medical Center in Los Angeles and the University of Texas Southwestern Medical Center argue that men and women experience diseases differently and metabolize drugs differently—therefore, clinical trial testing should both include more women and break down results by gender.

“Right now, when you go to the doctor and you are given a prescription, it might not ever have been specifically tested in females,” explained Deborah J. Clegg, co-author of the paper and a professor of biomedical science at Cedars-Sinai, in a press release. “Almost all basic research—regardless of whether it involves rodent models, dogs, or humans—is predominately done in males. The majority of research is done with the assumption that men and women are biologically the same.”

Decades ago, activists saw some headway with this issue: In 1993, a law called the NIH Revitalization Act was passed, requiring the inclusion of both men and women in the National Institute of Health’s clinical research. Despite the effort, however, women are still poorly accounted for in studies. And the consequences can be deadly.

Take cardiovascular disease, which kills more women than any other ailment. It also presents itself differently in women versus men. Yet a mere 35% of clinical trial subjects in cardiovascular research are women, and only 31% of those studies break down outcomes by gender. So even with a disease that kills women at greater rates than men, women are still underrepresented in the search for better treatment options.

“Although the number of women in NIH-sponsored clinical trials has increased since passage of the NIH Revitalization Act in 1993, it is still not enough, given the prevalence of Cardiovascular Disease in women,” stated a 2014 report by Brigham and Women’s Hospital in Boston.

That same report also pointed out that death rates for men with cardiovascular disease are decreasing at a faster rate than those for women.

Or take depression, which often involves issues with hormone production and regulation in the brain—and consider the fact that hormone production and balance work differently in men and women. Notably, women experience a 50% higher disease burden from depression than men. (A technical way of saying they suffer more.) Yet fewer than 45% of animal studies on anxiety and depression use female lab animals, even though these disorders are twice as common in women.

These are just two examples of diseases in which women may pay a price for their lack of representation in research. As the paper in Cell Metabolism explains, many aspects of disease and disease prevention can change depending on a patient’s gender, largely due to chromosomal and hormonal differences.

So why are women getting shortchanged?

The short answer is women’s bodies are more complicated—and thus more time-consuming—when it comes to testing. A female’s hormone levels fluctuate throughout her menstrual cycle, which can impact the research. Not only that, some women take birth control pills or use IUDs, which can also affect hormone regulation. Then, as women age, they go through menopause, which once again dramatically changes hormone production.

What all of this means, though, is not that women should be excluded because they’re “complicated,” but that women who represent all of these categories—pre-menopausal and taking birth control, pre-menopausal and not taking birth control and post-menopausal—should be included in research.

As the researchers in Cell Metabolism argue, this inclusion is crucial when it comes to drug testing because all of these changes and fluctuations can impact how drugs are metabolized.

“Researchers are encouraged to critically think of the impact that their experimental design has on the hormonal profile and to accurately analyze the data focusing on the impact of sex, not only of the individual being studied but also of the cell in a dish,” write the researchers in the paper. “It is no longer acceptable to be blind to the influence of sex and gender, focusing research only on one sex or gender to the exclusion of the other.”

Other studies have pointed out the period problem as well.

“Basic science and drug research are often marred by a desire to avoid inconveniences associated with potential variations across the menstrual cycle in female animals,” stated the 2014 report from Brigham and Women’s Hospital.

Which is crazy, when you think about it. Given that women make up half the population and menstrual cycles are very normal yet can also cause major fluctuations in the body, it would make sense to test drugs during different stages of a woman’s cycle. That seems like common sense.

The NIH Revitalization Act may have been passed more than two decades ago, but more clearly still needs to be done. Just check out this chart from Brigham and Women’s, which analyzed the inclusion of females in studies on coronary heart disease in the years after the passage of the act:

Meanwhile, many drugs on the market today were approved years before the NIH Revitalization Act. When I asked Glegg if researchers should revisit those drugs, she said, “Oh, I think it is very necessary!” Past research, she noted, has also highlighted sex differences in the way analgesics and pain work in our bodies.

“It is not easy, and is way more expensive, to include both sexes into research study designs and experiments,” Glegg told me over email, “but if our goal is to eventually provide personalized medicine, it can’t become personalized unless we begin to factor sex, sex chromosomes, and sex hormones into research!”

Glegg adds, “The concept that men and women are the same is flawed—and one must remember that as women, we are significantly different hormonally and metabolically between the pre-menopausal and post-menopausal portions of our lives. Research needs to take into consideration not only ‘females’ but, when and in what phase of our reproductive cycle the research is being conducted and when during our aging process. Only when we factor in all of these variables will we ever be able to provide true personalized medicine.”

Taryn Hillin is Fusion’s love and sex writer, with a large focus on the science of relationships. She also loves dogs, Bourbon barrel-aged beers and popcorn — not necessarily in that order.