Estrogen and progesterone are hormones that are produced by a woman’s ovaries.

Estrogen thickens the lining of the uterus, preparing it for the possible implantation of a fertilized egg. Estrogen also influences how the body uses calcium, an important mineral in the building of bones. In addition, estrogen helps maintain healthy levels of cholesterol in the blood. Estrogen is necessary in keeping the vagina healthy.

As menopause nears, the ovaries reduce most of their production of these hormones. Lowered or fluctuating estrogen levels may cause menopause symptoms such as hot flashes, and medical conditions such as osteoporosis.

Hormone therapy (HT) is a treatment that is used to supplement the body with either estrogen alone or estrogen and progesterone in combination. When the ovaries no longer produce adequate amounts of these hormones (as in menopause), HT can be given to supplement the body with adequate levels of estrogen and progesterone. HT helps to replenish the estrogen, relieving some of the symptoms of menopause and helping to prevent osteoporosis.

Progesterone is used along with estrogen in women who still have their uterus. In these women, estrogen– if taken without progesterone–increases a woman’s risk for cancer of the endometrium (the lining of the uterus). During a woman’s reproductive years, cells from the endometrium are shed during menstruation. When the endometrium is no longer shed, estrogen can cause an overgrowth of cells in the uterus, a condition that can lead to cancer.

Progesterone reduces the risk of endometrial (uterine) cancer by making the endometrium thin. Women who take progesterone may have monthly bleeding, or no bleeding at all, depending on how the hormone therapy is taken. Monthly bleeding can be lessened and, in some cases, eliminated by taking progesterone and estrogen together continuously. Women who have had a hysterectomy (removal of the uterus through surgery) typically do not need to take progesterone. This is an important point, because estrogen taken alone has fewer long-term risks than HT that uses a combination of estrogen and progesterone.

There are two main types of HT:

HT is prescribed to relieve:

Other benefits of taking HT include:

While HT helps many women get through menopause, the treatment (like any prescription or even non-prescription medicines) is not risk-free. Known health risks include:

Most of our understanding about the benefits and risks of hormone growth therapy on the heart and breast come from the Women’s Health Initiative (WHI) study (one of the largest studies done on hormone therapy):

Recent analysis of WHI actually shows that the risk of heart disease may be related more to the advanced age of the participants as opposed to the HT. The study also found that HT given to younger women, at the onset of menopause, appeared to lower the risk of heart disease. More specifically:

An increased risk of heart disease is only seen in women taking long-term estrogen-progestin combination therapy (EPT) if they start HT in their mid-60s (or after 10 years from menopause). There does not seem to be an increased risk of heart disease when women start EPT in their 50s (or within 10 years of menopause). Estrogen alone (ET) has not been shown to increase the risk of heart disease. Analysis of the age since menopause actually shows a lower risk of heart disease when ET was started in younger women (those just beginning menopause).

Currently, it is not recommended to use hormone therapy solely for the purpose of preventing heart disease. However these studies give us reassurance that when women just newly approaching menopause need HT for a short time, it is safe to do so in terms of long term heart disease risk.

Diagnosis of breast cancer increases when combination EPT is used beyond 3-5 years. This means that out of 10,000 women who use estrogen progestin therapy for more than 5 years, there will be 8 additional breast cancers diagnosed. In contrast, the WHI study showed women who use estrogen alone had no increase in risk of breast cancer even after 11 years of use. In fact, fewer breast cancers were seen in the group taking estrogen alone, though this was not statistically significant. When a woman comes off of hormone therapy, any potential increase in her risk of breast cancer quickly goes back to her baseline norm. This is why hormone therapy can be a safe option when women in their 50s (who are generally at lower risk for breast cancer compared to older women).

One of the problems with the WHI study, which gave us much of our knowledge on the risks of HT, is that most women in the study were starting hormones in their mid-60s. Typically, women who need HT are newly menopausal, in their early 50s. Younger women in the WHI study had fewer risks and more benefits from HT. Newer studies are trying to understand the risks and benefits of HT in women in their 50s. One such study showed HT started early in postmenopausal women significantly reduced death rate, heart attacks and heart failure. These postmenopausal women who started HT early and used it for more than 10 years were not at increased risk of breast cancer or stroke.

HT is not usually recommended for women who have:

Like almost all medications, hormone growth therapy has side effects. The most common side effects are:

Less common side effects of hormone therapy include:

Adjusting either the dosage or the form of the hormone replacement therapy medication you are taking can often reduce side effects of HT. However, you should never make changes in your medication or stop taking it without first consulting your doctor.

The balance of risks versus benefits of Hormone Replacement Therapy can be very different for each woman, depending on her age, family history, and personal medical history. It is important to allow enough time at an office visit to discuss the risks and benefits of hormone therapy. This is a question that should usually be addressed at a separate office visit to allow plenty of time for detailed discussion with your doctor.

Since research on HT is ongoing, women should reevaluate their treatment plans each year. Discontinue HT (under your health care provider’s guidance) if you develop a medical condition that would make it less safe for you.

It’s important that you do not make any abrupt changes to your HT without consulting your doctor. He or she can discuss with you the benefits and risks of HT based on your individual circumstances.