Why Do Cramps Happen? Prostaglandins and Menstrual Pain
The biological mechanism of dysmenorrhea: uterine muscle contractions driven by prostaglandins, and when to speak with a doctor.
Cycle literacy - Body & Symptoms, about 3 min read
Prostaglandins: The Body's Messengers
Primary dysmenorrhea (menstrual cramping without an underlying pelvic disease) is primarily caused by natural chemical messengers called prostaglandins.
As the uterine lining begins to break down before menstruation, cells release prostaglandins. These compounds stimulate the smooth muscles of the myometrium (uterine wall) to contract, helping shed the endometrial tissue.
Why Cramping Peaks Early
Prostaglandin levels are highest on the first day or two of a period, which is why cramps are usually worst on Cycle Days 1 and 2.
Prostaglandins can also affect the gut, causing loose stools or nausea, and period pain often spreads to the lower back and thighs.
While mild to moderate cramps are very common, pain that interferes with school, work, or daily activities warrants an evaluation by a healthcare professional. Get help urgently if pain is severe and pain relievers haven't helped, or if it's much worse than usual — in the UK, ask for an urgent GP appointment or contact NHS 111. Pain that keeps getting worse over months is also worth checking.