Understanding 'Period Poops': Why Menstrual Cycles Affect Digestion

Every period, right on schedule: the cramps arrive, and right behind them, the urgent need to poop.

If this is your experience, you’re in good company: in one study, 73% of healthy premenopausal women reported at least one significant gastrointestinal symptom in the days before or during their period. Abdominal pain and diarrhea were the most common complaints, but women reported nausea and constipation too.

Menstrual and digestive discomfort often coincide: “If you ask women about ‘period poops’ they’ll tell you they’re having menstrual cramps and those GI cramps at the same time,” said Taylor Judkins, a nutrition researcher at the University of Florida who has spent more than a decade studying the phenomenon.

Period-related GI symptoms are common enough to have their own moniker. The science, however, has barely kept up. Judkins has personal experience with the phenomenon; when she first went looking for research on the phenomenon as a university student, she found almost nothing. A decade later, she says, there’s still a lot to learn.

Why do period poops happen?

It all starts with the uterus. As your period approaches, levels of estrogen and progesterone fall sharply. That’s the signal for your body to start breaking down the uterine lining, which you start shedding on day one of your period.

At the same time, cells in the uterus start making hormone-like compounds called prostaglandins. These cause contractions in the type of muscle cells that make up most of your uterus and digestive tract, among other effects.

It’s unclear exactly what happens next. But the leading theory, said Judkins, is that some prostaglandins enter the bloodstream from the uterus and stimulate similar contractions in the neighboring gut. This would explain the intestinal cramping and diarrhea many experience alongside menstrual cramping, especially on the first day or two of their periods.

One other theory relates to the vagus nerve, which runs signals between the gut and the brain. This neural pathway is highly sensitive to stress signals and inflammation. When activated, it provokes fluid release within the gut and increased contractions of its muscles, leading to diarrhea. This is why some experts believe many people get an upset stomach when they’re anxious. Judkins theorizes that menstruation may also trigger the pathway.

Many women also note constipation one to two weeks before their periods start, says Judkins, which may be a consequence of high progesterone levels. However, the evidence is less clear on the prevalence and timing of that symptom.

People with irritable bowel syndrome and inflammatory bowel disease tend to have significantly worse symptoms around their periods, and those with endometriosis typically carry a higher burden of GI symptoms overall. But you don’t need an underlying diagnosis to have period poops.

“It’s very common, and some will tell you that it’s normal,” she says, “but it doesn’t mean you should have to live with this drastic decrease in your quality of life.”

Can anything reduce period gut symptoms?

Options exist, but none are a clear fix.

Judkins and her team ran the only randomized trial to date testing the effects of probiotics on menstrual GI symptoms. Probiotics improved indigestion – but not diarrhea, the symptom most people are actually trying to solve.

Some experts recommend oral contraceptives on a theoretical basis: they reduce the amount of endometrial tissue your body makes, which should lead to less prostaglandin production when that tissue gets shed. However, there’s no good evidence suggesting they are effective for GI symptoms; one of Judkins’ studies that exclusively enrolled women taking oral contraceptives found they also reported period poops.

Anti-inflammatory drugs such as ibuprofen and naproxen reduce prostaglandin production, which can ease both uterine and digestive-tract cramps. The catch: they can irritate the gut lining and actually cause diarrhea, and for anyone with Crohn’s disease or ulcerative colitis, they can worsen symptoms and should generally be avoided.

For now, diet is your most practical starting point. Judkins recommends staying hydrated and eating more fiber – fruit, vegetables, whole grains, legumes — and less greasy comfort foods, which tend to worsen diarrhea. Exercise helps some people; the data aren’t robust, but the risk is low. And if symptoms are severe enough to affect work or daily life, that’s worth raising with a doctor.

Why isn’t there a solution for this common issue yet?

Judkins began studying period gut over a decade ago. “When you search these keywords, it’s my name that comes up,” she says.

That’s not a triumphant statement. It reflects a research culture that has treated menstrual health as a niche concern rather than an important issue affecting roughly half the population.

When researchers don’t study something, clinicians are less likely to treat it. Patients are also less likely to raise it, because nobody has signaled that it’s worth mentioning or that anything can be done. Judkins hopes that changes. “Funding for women’s health research is ultimately a gain for everybody,” she says.