Dosing of all the hormones is best done to mimic the normal menstrual cycle of the woman of childbearing age. To keep things simple, one physician recommends that pre- and postmenopausal women begin on the first day of the month taking their estrogen formulation from day 1 to day 25. The progesterone is used from day 1 to day 20. One must bear in mind that while progesterone is protective in the sense that it protects against cancer, estrogens that are taken without progesterone, may increase a woman's risk of cancer of the breast and potentially the uterus. This is very easy to understand.
Estrogens stimulate breast tissue and the lining of the uterus.
During the menstrual cycle, progesterone production rapidly falls, resulting in the shedding of the uterine lining and menstrual flow. If estrogen is taken continually, building up the uterine lining without opposing progesterone, there is a theoretical increased cancer risk. This is why you must discuss this with a physician knowledgeable about the subject. The risk is minimized in a postmenopausal woman if hormone replacement results in monthly menstruation or if she undergoes yearly uterine tissue sampling or biopsy, which is a simple procedure done in the doctor's office. Women over 30, particularly those with a family history of osteoporosis, should consider hormone level analysis in consultation with a physician to see if hormone supplementation should be undertaken prior to menopause.