Can stress cause irregular periods?
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Regulation of menstrual periods is controlled by a complex hormonal balance. Likewise, the body's reaction to stress involves changes in the levels of many hormones. Because it affects hormone balance and many other processes in the body, psychological stress can also interfere with the menstrual cycle. In fact, stress is considered to be a common cause of missed or late menstrual periods.
"Physiology of the normal menstrual cycle"