Estrogen is produced in the ovaries, adrenal glands and fat tissues. It prepares the reproductive organs for conception and pregnancy. Estriol, a form of estrogen, is produced by the placenta during pregnancy.

The function of estrogen in the body is complex. We have learned a lot, but there is still much more to learn.

Declining or low levels of estrogen can cause physical symptoms including hot flashes night sweats and vaginal dryness.

By the time you reach menopause, you will produce only about one-third the amount of estrogen you produced during your childbearing years.

Supplemental estrogen taken after menopause does not appear to prevent heart disease when initiated in older women several years past menopause.

The U.S. Food and Drug Administration and other agencies have adopted new terminology to describe hormone regimens used to replace hormones that decline with the onset of menopause or are deficient as a result of medical conditions. The term, "replacement" has been dropped from "hormone replacement therapy." Instead, estrogen-only therapy is called estrogen therapy, or ET, and estrogen/progestin or estrogen/progesterone therapy is called hormone therapy, or HT.

The term "estrogen" includes a group of closely related compounds, including estradiol, estrone and estriol.

Estrogen therapy may be prescribed for conditions such as delayed onset of puberty, genital atrophy, or female hypogonadism (incomplete functioning of the ovaries, creating symptoms such as vaginal dryness, breast atrophy and lower sex drive).

There is new evidence that long-term use of estrogen alone therapy may increase a women's risk of ovarian cancer.

New findings from a memory sub-study of the Women's Health Initiative (WHI) indicate that women who are older than 65 when they start taking combination hormone therapy have an increased risk of developing dementia, including Alzheimer's disease, compared with women who do not take the medication.