WebMD Answers
As with PMS (premenstrual syndrome), the exact cause of PMDD (premenstrual dysphoric disorder) is not known. Most researchers, however, believe PMDD is brought about by the hormonal changes related to the menstrual cycle. Recent studies have shown a connection between PMDD and low levels of serotonin, a chemical in the brain that helps transmit nerve signals. Certain brain cells that use serotonin as a messenger are involved in controlling mood, attention, sleep, and pain. Therefore, chronic changes in serotonin levels can lead to PMDD symptoms.
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