Cramps are uterine contractions that are stimulated by chemicals called prostaglandins. Prostaglandins are released from the lining of the uterus right before and during menstruation. The uterine muscles contract and the pain is commonly felt in the back, pelvis and legs. Most girls experience menstrual cramps during the first one or two days of their periods. On average, U.S. girls begin to menstruate at about 12.5 years, although periods may begin anywhere between age 9 and 16.
Menstrual cramps occur in girls who are ovulating most months.
Older teen-age girls, then, are more likely to have cramps with every period. Medications that have an anti-prostaglandin effect are especially helpful for menstrual cramps. In years past, many girls took aspirin products for menstrual cramps, with good results. Aspirin worked because it is an anti-prostaglandin medication. For about the last 20 years, however, aspirin has not been recommended for children or adolescents because aspirin use has been associated with a very serious illness called Reyes' syndrome.