It’s about time.
With as many advances as we’ve seen recently in women’s health — from endometriosis being able to be diagnosed without surgery, to completely rethinking and renaming PCOS, now more accurately, PMOS — we still have a long way to go in terms of understanding how medications affect the sexes differently.
It’s often only after a drug is released do we learn women might be affected totally differently from men — as with the case for two recent major studies.
Specifically, the new research points to the role of estrogen, which naturally ebbs and flows over the course of a menstrual cycle.
Changing levels of estrogen has major impacts across the entire body under normal circumstances. Introduce medication into the mix, and it becomes a whole different ballgame.
“For too long, the menstrual cycle has been treated as background noise in health research,” said Poppy Cooper, an author of one of the recent studies. “This work is part of a growing shift in that thinking and a recognition that the menstrual cycle has impacts beyond reproductive health.”
Here’s which medications researchers are learning could be impacted by menstrual changes.
COVID-19 vaccine
After the COVID-19 vaccine was rolled out in 2021, people quickly caught on that the shot affected women differently.
Researchers found that there were “small and temporary” changes to menstrual cycles after women were vaccinated — on average, the entire cycle (about 28 days) increased by about half a day.
It took another five years to find that where women were in that cycle when they got the vaccine affected how effective the vaccine was.
Researchers in a June study found that women who were vaccinated at the follicular phase, about a 10-20 day stretch that starts on the first day of bleeding, were 35% more likely to get side effects than those who got the shot in the luteal phase, the span just before the period comes back.
People vaccinated during the follicular phase avoided infection for 200 days longer than those who got the vaccine during the luteal phase.
“This study treats the menstrual cycle as a variable that matters rather than a confounding variable to simply control away,” Julia Craggs, a women’s health doctor, told New Scientist. “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.”
A once-failed drug that hoped to cure Alzheimer’s
A decade ago, a drug called davenutide was being tested to treat a rare brain disorder called progressive supranuclear palsy (PSP). It failed in 2012, when researchers found it wasn’t effective at treating the disorder.
The drug was supposed to help with accumulated tau proteins, which also drives Alzheimer’s, frontotemporal dementia, and schizophrenia.
In 2023, the data was re-examined. Researchers found that women responded to the drug while men did not — something that was hidden when they were grouped together.
In research released this summer, the drug, a nasal spray, was tested on mice — they found that when female mice had the highest estrogen levels, they took up more of the drug than the males did.
In a small human trial (two men and six women), the results matched: women took up the drug more than men did.
Estrogen plays a role in blood flow around the brain and what gets through the blood-brain barrier, which could help explain why women respond better to this drug.
The drug is now back in development in Tel Aviv.
Dozens of other drugs
A 2025 review showed that estrogen can affect drugs metabolized by CYP enzymes — and there are many.
CYP enzymes are found in the liver, and are responsible for breaking down drugs and clearing out toxins. They metabolize between 50% to 80% of common clinical drugs.
Everything from Motrin (ibuprofen) to caffeine, Prilosec (omeprazole), Xanax (alprazolam), and Viagra (sildenafil) all get processed by CYP.
Fluctuating estrogen could affect how the liver processes these medications, the study showed.
For example, two CYP enzymes, CYP1A2 and CYP2C19, were suppressed by estrogen, making it harder for drugs to be metabolized along their pathways.
