If you’ve ever noticed that you’re constipated the week before your period, then suddenly can’t stay out of the bathroom once it arrives — you’re not imagining it, and you’re far from alone.
What most people don’t realise is that your digestive system and your menstrual cycle are closely linked. The same hormones that govern your cycle also directly influence how your gut moves. Understanding this can save you a lot of confusion — and unnecessary worry.
Your menstrual cycle is driven by two main hormones: oestrogen and progesterone.
In the first half of your cycle, oestrogen is the dominant hormone. After ovulation, progesterone rises and takes over. If pregnancy doesn’t occur, both hormones drop sharply — triggering the start of your period.
This hormonal rhythm affects far more than your uterus. Progesterone, in particular, is known to slow gut motility — meaning it slows down the movement of food through your digestive tract. This is why the week or two after ovulation, when progesterone is at its highest, is often when constipation and bloating feel worst.
Then, just before your period begins, both hormones fall quickly. This drop causes the muscles lining your intestines to contract more rapidly — speeding things up and often resulting in looser or more frequent stools in the first day or two of menstruation.
During menstruation, your body produces compounds called prostaglandins. These are hormone-like substances that play a role in inflammation, pain signalling, and uterine contractions — which is why they’re partly responsible for period cramps.
But prostaglandins also stimulate movement in the gastrointestinal tract. When their levels are elevated during your period, they can speed up gut activity alongside uterine activity — contributing to the loose stools and urgency that many women experience in the first day or two of their period.
For women with an already-sensitive gut — or conditions like irritable bowel syndrome (IBS) — this effect can be more significant. (If your menstrual bowel symptoms are severe or significantly impact your daily life, it’s worth speaking to a doctor, as conditions like endometriosis can also cause gastrointestinal symptoms that worsen during menstruation.)
Pre-period bloating is one of the most common PMS symptoms, and it’s the result of a few things happening at once.
Slower gut motility means food and gas move through your system more gradually, allowing more time for bloating to build. Hormonal shifts in the premenstrual phase can also cause fluid retention and increased pressure in the pelvic region, adding to that heavy, uncomfortable feeling in the lower abdomen.
There’s also evidence that gut sensitivity increases in the premenstrual phase, meaning normal amounts of gas can feel more painful than usual. Stress and anxiety are known to compound this, as psychological stress is well-established to heighten gut sensitivity generally.
When both are happening at the same time, it can be genuinely hard to tell what’s causing your discomfort. Here’s a rough guide, though individual experiences vary:
Bowel-related pain tends to feel colicky, may be centred around the navel or spread across the abdomen, and often improves after a bowel movement.
Menstrual cramps are more typically felt in the lower abdomen or pelvis, often described as throbbing or cramping, and tend to peak in the first 24 to 48 hours of your period before easing.
If the pain improves after going to the toilet, it’s more likely to be digestive in origin. If it persists regardless, it may be menstrual — or both.
Mild changes in bowel habits throughout your cycle are generally normal. But speak to a doctor if you notice:
These could indicate an underlying condition such as IBS, endometriosis, or inflammatory bowel disease that may be worth investigating.
Your hormones don’t just affect your cycle — they influence your mood, energy, sleep, skin, and gut function throughout the entire month. If you’re experiencing significant premenstrual or menstrual symptoms, it may be worth taking a closer look at your hormonal health as part of a broader health assessment.
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