Menstrual pain (dysmenorrhoea)

On average, women have a menstrual period every 28 days with bleeding (menstruation) lasting approximately four to seven days. During this time, the muscles of the uterus contract in response to hormone-like substances called prostaglandins, produced by the lining of the uterus. The levels of the prostaglandins increase prior to menstruation, and peak at the start of the menses. The levels decline again as a woman menstruates, resulting in less uterine discomfort or cramps after the first few days of the menstrual period.