Diarrhea on your period is common, and it has a real cause. The same chemicals that make your uterus cramp can speed up your bowel. For most people it starts a day or two before bleeding, is worst on the first days, and is gone a few days in.
That’s the short version. Below is how common it is, why some people get constipation first, what helps, and the few signs that mean it’s something other than your period.
How common is diarrhea on your period?
Very. In a 2014 survey of 156 healthy women at a gynecology clinic in Winnipeg, 73% had at least one gut symptom around their period. Diarrhea was the second most common after stomach pain. 24% had it in the five days before their period and 28% had it during. None of them had a known bowel or gynecological condition.
The same survey found that women who felt low or anxious around their period were more likely to have two or more gut symptoms. So did women with period fatigue. The authors think the brain, the gut and the cycle hormones are tangled up together, and that a bad day in one often shows up in the others.
Why does your period give you diarrhea?
The usual explanation is prostaglandins. Your uterus releases them just before and during your period so its muscle contracts and sheds the lining. They aren’t picky about which muscle they reach. Cleveland Clinic explains that they can have the same effect on the bowel, which means more trips to the toilet and looser stools.
Hormones play a part too. Progesterone rises after ovulation and falls just before your period. A 2015 review of the research found that food moves through the gut more slowly in the second half of the cycle, when progesterone is high. When it drops, things speed up again.
One detail surprised us. A 1996 study had 53 women keep a daily diary for three cycles. Stomach pain and nausea rose and fell with their cramps, but diarrhea and constipation didn’t track cramp severity. So bad cramps don’t guarantee bad diarrhea, and a light period can still come with a rough gut.
How many days before your period can you get diarrhea?
The survey above counted the five days before a period, and about a quarter of the women had diarrhea somewhere in that window. Most people describe it starting the day or two before bleeding, which is when prostaglandins start to climb.
Some people get it a week ahead. If that happens to you every cycle, at roughly the same point, it’s very likely tied to your cycle too. The easiest way to know is to note it for two or three cycles and line it up against your period dates.
Constipation before your period, then diarrhea during
This is a common pairing. In the week or so before your period, progesterone is high and your gut is slower, so you may be constipated and bloated. Cleveland Clinic says progesterone-linked constipation tends to start around ovulation or a couple of days after. Then your period starts, progesterone falls, prostaglandins rise, and it swings the other way.
If you only get one half of the pair, that’s normal too. The same hormones affect people differently, and Cleveland Clinic notes that progesterone can cause diarrhea in some people and constipation in others.
Which day of your period is it worst?
Usually the first day or two. That’s when prostaglandin levels and cramps tend to be highest, and it’s why the advice on painkillers below is about starting early. If it carries on for your whole period, or keeps going after the bleeding stops, keep a note and mention it to a doctor.
What helps
- Start ibuprofen or naproxen early. MedlinePlus suggests taking an anti-inflammatory the day before your period is due and regularly for the first few days. These drugs lower prostaglandins, which is why Cleveland Clinic says they can ease period poops as well as cramps. Follow the dose on the pack.
- Drink more than usual. Diarrhea loses fluid. Water is fine, and an oral rehydration sachet helps if it’s heavy.
- Go easy on coffee. Cleveland Clinic points out that it’s a laxative, which is the last thing you need on day 1.
- Keep meals plain and warm. Soup, oats, rice or eggs on toast are easier on a gut that’s already moving fast than a big fatty meal.
- For the constipation half, add fiber and water in the week before your period, before it starts rather than once you’re already blocked.
If your periods are painful as well, our guide to how long a period lasts covers what counts as a normal one.
When it isn’t just your period
Period diarrhea follows your cycle and clears up. Get it checked if any of these apply.
- Blood in your stool, or bleeding from your bottom. The NHS says to get urgent advice from 111. Period blood on the toilet paper is different, but if you’re not sure which it is, ask.
- Diarrhea for more than 7 days. That’s longer than a period explains, and the NHS says to get advice.
- Pain when you poo. The NHS period pain page says to see a GP for pain when pooing or a change in how much you poo. Pain when you poo is also on the NHS list for endometriosis, and our guide to tracking periods with endometriosis explains what to log.
- Symptoms on days nowhere near your period. The 2015 review found that people with irritable bowel syndrome or inflammatory bowel disease often get worse during their period. If your gut is bad all month and only worse around your period, the period isn’t the whole story.
How to tell whether it’s your cycle
Write it down for two or three cycles. Mark the first day of each period, and on each day you have diarrhea or constipation, note which. If the bad days land in the same place each cycle, you’ll see it, and so will a doctor if you need one. A period diary is all this takes.
How Plum fits in
We make Plum, a period tracker app, so here’s what it does for this. Stool has its own category in Plum, with constipation and loose stool as options, and digestion is separate with bloating, gas and nausea. You can log them on any day, not only period days, which is how you see whether they cluster before your period.
When you’ve logged loose stools, constipation or bloating, Plum is more likely to pick its tip on soft, warm meals for your period days. Plum also predicts your next period, so you know when to start the ibuprofen. It won’t tell you whether your symptoms point to IBS or endometriosis. That takes a doctor. We read every source on this page on October 20, 2026.
Plum shows no ads and never sells personal data. It needs an account and syncs your data to our servers, encrypted in transit and at rest. If you’re in a group with friends, they see a summary of your cycle dates and never your symptoms.
