Premenstrual syndrome (PMS) is the term used to describe a group of physical or behavioral changes that some women go through before their menstrual periods begin every month. PMS can produce discomfort in different parts of the body and cause unpleasant emotional feelings.

For reasons that remain unclear, these physical discomforts or mood changes begin at various times near the end of the menstrual cycle and usually disappear after a woman has begun her menstrual period. They reappear at about...