When a woman of childbearing age, approximately 15 to 44, does not have a regular menstrual cycle, a period can be induced by administration of hormones, according to WebMD. Additionally, treatment of any underlying disease causing the menstrual irregularities may cause the woman's period to resume regularly.
WebMD indicates that a health care provider might prescribe hormone therapy to start a woman's period. Commonly, either progestin or the hormone progesterone is used to trigger a period. In some cases, lifestyle changes also induce a period. Excessive or sudden weight gain or loss can sometimes prevent a period, and stress is also a cause of menstrual irregularities in some women.