March 23, 2010 -- An experimental new drug may ease menstrual cramps by targeting the cause rather than the symptom of the pain. Researchers say the drug, now in phase II clinical trials in the U.K. and U.S., works by blocking the hormone vasopressin, which is involved in contractions of the uterus. Increased levels of this hormone are believed to cause the pain associated with menstrual cramps. Menstrual cramps, known in medical terms as dysmenorrhea, affect more than 50% of women of childbearing age. They occur when the smooth muscles of the uterus contract with increasing frequency. The most common symptoms are abdominal and back pain, but dysmenorrhea may also cause nausea, vomiting, sweating, and dizziness. Treatments for dysmenorrhea include pain relievers, anti-inflammatory drugs, and contraceptives that stop menstruation. But researchers say these only relieve the symptoms of the condition rather than the underlying cause and may have unwanted side effects. "We hope th...