This too can be treated by cycling with birth control pills, or possibly by initiating therapy for cyclic hormonal treatment of menopause if it appears that the woman is perimenopausal. Hypothyroidism, or inadequate thyroid hormone production, is another fairly common cause of excess menstrual bleeding. Medication interactions are a common cause of spotting in between periods in women on the pill. Antibiotics can often cause this. Stress is perhaps the most common cause of a missed period in nonpregnant women.
Stress stimulates production of adrenal hormones which interfere with the normal ovulatory cycle.
Anovulatory cycles due to an immature hormonal loop in younger women especially can cause infrequent periods. See the section on anovulatory cycles above. Medication interactions, especially in women on the pill, also missed pills can cause a cycle to become irregular. Rarely when the periods cease and nipple discharge is present a tumor called a pituitary adenoma is the cause. Your doctor can draw a prolactin level to check for this problem.