Premenstrual syndrome (PMS) is a disorder marked by physical and emotional symptoms. It affects women 1-2 weeks before the beginning of their menstrual period.

The Menstrual Flow
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The cause is unknown. A combination of environmental, metabolic, and behavioral factors may make women vulnerable to the specific actions of hormonal changes linked to menstruation. A brain chemical, serotonin, may play a role in severe forms of PMS.