Medical Research Is Finally Studying Women as Women, Not Small Men

For decades, drug trials mostly treated women as smaller men. Same dosing math, same trial design, hormones ignored. A stack of new research says that was a mistake, and it's starting to show exactly how much data got lost along the way.

Start with COVID-19 vaccines. A study covered by New Scientist and cited by the New York Post found that women vaccinated during the follicular phase of their cycle, roughly the 10 to 20 days starting on the first day of a period, were 35% more likely to experience side effects than women vaccinated during the luteal phase, the stretch right before the next period. The same study found women vaccinated during the follicular phase avoided infection for 200 days longer than those vaccinated during the luteal phase.

Julia Craggs, a women's health doctor quoted by New Scientist, said the implications go beyond one vaccine. "We may be sitting on a significant source of unexplained variation in how women respond to treatment and we have simply never looked in that direction," she said. Poppy Cooper, an author of the research, put it more bluntly: "For too long, the menstrual cycle has been treated as background noise in health research."

That blind spot has already cost real drugs a chance at approval. Davenutide, a treatment tested a decade ago for the rare brain disorder progressive supranuclear palsy, failed its trial in 2012 and was shelved. In 2023, researchers went back and reanalyzed the data by sex. Women had responded to the drug. Men hadn't. Lump the two groups together, as the original trial did, and the effect disappears into statistical noise. A drug that might have helped women with a devastating brain disease got written off because nobody split the results by sex until 11 years later.

The brain itself changes shape with the cycle

Separately, a University of Delaware team published findings in Brain Communications showing that estrogen fluctuations physically alter brain tissue mechanics in the hippocampus, the region tied to memory and learning. Using an imaging technique called magnetic resonance elastography, researchers tracked these changes across the reproductive cycle in rats.

"Across the reproductive cycle, the brain adapts, relying more heavily on different regions at different times," said Katrina Milbocker, the study's first author and a postdoctoral researcher at the University of Delaware. "This was step one: can we track these changes with MRE in rats, and then eventually in humans?"

Curtis Johnson, an associate professor of biomedical engineering who led the lab, said the team is now studying rat models of menopause on the theory that a sudden drop in estrogen might cause what he called a mechanical "stuck state" in brain tissue, one that could help explain the brain fog many women report during menopause. That's a hypothesis under active testing, not a settled finding. The team is also working to translate the rat data into human studies, though that work hasn't produced results yet.

GLP-1 drugs and PCOS: promising but unproven at scale

A third thread involves GLP-1 drugs like semaglutide, now being tested for the hormonal disorder that's been renamed PMOS (formerly polycystic ovary syndrome, or PCOS). The Associated Press, cited by LiveNOW from FOX, reported that in one trial published in the journal Fertility and Sterility, 8 of 11 participants who completed the study lost roughly 10% of their body weight, with a median loss of about 42 pounds and a median 52% drop in testosterone. Six women had more periods, and four returned to monthly cycles.

Dr. Melanie Cree, who directs a PMOS clinic at Children's Hospital Colorado and has led three separate GLP-1 studies for the condition, told the AP that most women with PMOS have insulin resistance, meaning the hormone doesn't function properly. Across her three studies, women taking GLP-1 drugs lost more weight than control groups and saw drops in testosterone, blood sugar, and insulin.

That said, the sample sizes are small, some researchers told the AP the evidence remains uncertain, and GLP-1 drugs are not approved by the FDA to treat PMOS. Doctors are prescribing them off-label, and the AP noted insurance often won't cover the cost because of that status. Anyone expecting a quick fix should know this is still early-stage research, not a settled treatment protocol.

What's actually new here

None of this is a discovery that estrogen affects the body. That's been known for a century. What's new is that researchers are finally treating female hormonal cycles as a variable worth measuring instead of noise to average out. The FDA didn't require that clinical trials include women in appropriate numbers until 1993, and even after that mandate, sex-based analysis of trial data has often lagged.

The unresolved question is how many other approved drugs, on the market right now, have hidden sex-based effects nobody has bothered to check because the industry standard for so long was to design around a male default. The davenutide case shows what happens when someone finally looks: a drug written off as a failure turns out to work for half the population studied. Nobody knows how many more davenutides are sitting in old trial data, unexamined.