Cramps are the uterus doing its job — loudly
When progesterone crashes at the end of the luteal phase, the endometrial lining releases a burst of prostaglandins — inflammatory molecules that make the uterus contract so it can shed.
The higher your prostaglandin levels, the stronger the contractions. And because prostaglandins circulate in the bloodstream, they also cause the diarrhoea, nausea, and headache many people get with their period. That's not a coincidence, it's chemistry.
Referred pain: why it hurts everywhere
Uterine nerves share pathways with nerves from the lower back, thighs, and pelvic floor. Pain signals get 'referred' — the brain can't always tell exactly where the pain is coming from, so it lights up a wider area.
This is why period pain can radiate down the legs or across the lower back, and why it can feel like a UTI or a bowel problem to someone who isn't used to it.
What helps (and why)
- NSAIDs (ibuprofen, naproxen)
- Block prostaglandin production directly. Most effective when started 24 hours before pain, if you can predict it.
- Heat
- Increases blood flow, relaxes uterine muscle. Studies find it as effective as ibuprofen for many people.
- Combined pill / IUS
- Thin the endometrium so there's less lining to shed and fewer prostaglandins to release.
- Movement
- Aerobic exercise reduces prostaglandin sensitivity over time.