Hormone replacement therapy (HRT) is medication containing one or more female hormones, commonly estrogen plus progestin (synthetic progesterone). Some women, usually those who have had their uterus removed, receive estrogen-only therapy.

HRT is most often used to treat symptoms of menopause such as hot flashes, vaginal dryness, mood swings, sleep disorders, and decreased sexual desire. It comes in the form of a pill, patch, or vaginal cream.

Based on early studies, many health care providers used to believe that HRT might help reduce the risk of heart disease and bone fractures caused by osteoporosis, in addition to treating menopausal symptoms. The Women's Health Initiative (WHI) study led health care providers to revise their recommendations regarding HRT.

The study was partly intended to examine the health benefits and the risks of hormone replacement therapy, including the risk of developing breast cancer, heart attacks, strokes, and blood clots. It showed that women who took estrogen with or without the hormone progesterone for 5 or more years had an increased risk for stroke, heart disease, breast cancer, and blood clots.

The information below includes detailed information from the WHI study about each risk. A summary follows at the end.

ALZHEIMER'S DISEASE

Studies have not shown that HRT slows down the symptoms of Alzheimer's disease. Further research is ongoing to determine whether there is any benefit to HRT with regard to other memory loss.

BLOOD CLOTS/THROMBOEMBOLIC DISEASE

The increased risk of blood clots from taking estrogen has been recognized for years. Generally, this risk has been associated with the use of birth control pills that contain high doses of estrogen. The risk is even higher if you smoke.

The WHI study confirmed an increase in the number of blood clots in women taking estrogen/progestin.

BREAST CANCER

The WHI estrogen/progestin trial was stopped primarily because of an increased risk of breast cancer found in women taking HRT. The second part of the WHI study looked at estrogen alone in women who no longer have a uterus and did not find any increased risk of breast cancer.

COLON CANCER

The WHI study found a lower risk of colon cancer in women who took estrogen/progestin than in women not on HRT. Further studies are needed to confirm these results.

DEPRESSION

Studies have shown that women who suffer from common vasomotor symptoms of menopause, mood swings, and sleep problems benefit from HRT in the overall quality of their life. However, there is no scientific evidence that HRT is helpful in the treatment of major depression.

GALLBLADDER DISEASE

Several studies have shown that women who use estrogen/progestin therapy are at increased risk of developing gallstones.

HEART DISEASE

Estrogen helps decrease bad cholesterol (low density lipoprotein, or LDL) and increase good cholesterol (high density lipoprotein, or HDL). Lower levels of LDL and higher levels of HDL are associated with a decreased risk of heart disease. Researchers theorized that HRT should lower risk by changing these levels. The WHI showed that this is not true.

The number of heart attacks increased among women taking estrogen and progestin. Further research by the Heart Estrogen/progestin Replacement Study (HERS) showed that estrogen and progestin had no benefit for the heart.

HRT should not be prescribed strictly for the prevention of high cholesterol or heart disease. Lifestyle changes and medications to lower cholesterol and control blood pressure are recommended for those conditions.

MENOPAUSE SYMPTOMS

During menopause, the amount of estrogen produced by a woman's ovaries drops. These naturally occurring low estrogen levels may cause symptoms that include hot flashes, sleep problems, mood swings, and vaginal dryness.

Most women see relief from the hot flashes, sleep difficulties, and vaginal dryness within a few weeks of taking HRT. Short-term use (2-4 years) of the lowest possible dose of HRT to treat the symptoms of menopause still appears to be safe at this time. Usually, hot flashes and night sweats are less severe after a couple of years -- especially if HRT is slowly reduced.

OSTEOPOROSIS

A woman's body produces less estrogen during and after menopause, which may affect her bone strength. The WHI study showed that women taking HRT had 34% fewer hip fractures and 24% fewer fractures than women not receiving hormones.

However, the short-term use of HRT to relieve symptoms at the time of menopause does little to prevent fractures in women when they reach 75-80 years of age. Women who take estrogen to maintain bone density must continue taking estrogen because the beneficial effects on bones disappear when it is discontinued.

Estrogens are still used to prevent osteoporosis but are not approved to treat a woman who has already been diagnosed with the condition. If you are considering taking HRT to prevent osteoporosis, discuss the risks with your doctor.

For more information on preventing and treating boss density loss, see the article on osteoporosis.

OVARIAN CANCER

A study published by the National Cancer Institute in 2002 found that women who use estrogen therapy alone have an increased risk of developing ovarian cancer. This risk increases with the number of years a woman uses estrogen.

For women who used estrogen for 20 or more years, the risk of ovarian cancer was three times that of women who did not use estrogen.

This study did not have enough women to assess the potential risk of an estrogen/progestin combination on the risk of ovarian cancer.

STROKES

The WHI study showed an increase in strokes among the women taking estrogen/progestin. An increased risk of stroke was also seen in the estrogen-only therapy.

UTERINE CANCER/ENDOMETRIAL CANCER

Taking estrogen alone causes the lining of the uterus to grow. The risk for endometrial cancer is six to eight times higher in women who take estrogen, compared with those who do not.

Progestin works to decrease the lining of the uterus. For women who still have their uterus, most doctors prescribe progestin (a synthetic progesterone) to counteract the effect of the estrogen.

The WHI study did not find any difference in endometrial cancer rates between the women who took hormones and those who did not. Depending on the form of HRT, taking progestin may cause bleeding similar to a period. This combination of estrogen and progesterone may be in the form of one pill, or it may be two separate pills.

URINARY INCONTINENCE

HRT has not been found to improve or reduce the incidence of incontinence after menopause.

SIDE EFFECTS FROM HRT

As with all medicines, there are side effects associated with HRT. Some women taking HRT may experience water retention, bloating, nausea, breast soreness, mood swings, and headaches. Changing the dosage or the form of HRT may help to reduce these side effects.

Some women have irregular bleeding when they start taking HRT, but changing the dosage often eliminates this side effect.

SUMMARY OF RISKS/BENEFITS

The WHI study shows relatively small absolute increases in the risk of heart disease, breast cancer, blood clots, and stroke to an individual woman. However, when the entire population of postmenopausal women and the number of years a woman may be on HRT are considered, the number of strokes, heart attacks, breast cancer cases, and blood clots appears to outweigh the protective effect of HRT on bones.

Some women may still wish to consider HRT for short-term treatment of menopausal symptoms. The key is to weigh the risks associated with taking HRT against a particular woman's risk of heart disease or osteoporosis without taking HRT. Every woman is different. Your doctor should be aware of your entire medical history when considering prescribing you HRT.

FORMS OF HRT

HRT is available in various forms, including pills, patches, and vaginal creams. Your health care provider will start you on a regimen that is best suited for you. It may be necessary to try more than one regimen before finding the one that works best for you.

• Cyclic hormone therapy is often recommended. With this therapy, estrogen is taken in pill form for 25 days, with progestin added somewhere between days 10 - 14. The estrogen and progestin are taken together for the remainder of the 25 days. Then, no pills are taken for 3 - 5 days. There may be monthly bleeding with cyclic therapy.
• Continuous, combined therapy is where estrogen and progestin are taken together every day. When this therapy is started, or when switching from cyclic to continuous therapy, women may experience irregular bleeding. Most women stop bleeding within 1 year after starting this therapy.
• An HRT patch can be applied to the abdomen or the thigh. The patch allows the estrogen to be absorbed through the skin into the bloodstream. Some women prefer this method because they do not have to take pills.
• Vaginal cream containing estrogen may be given to women for vaginal dryness. The cream is usually given along with one of the other forms of HRT because the cream may not relieve many of the other symptoms and does not appear to protect against bone disease.

Additional medications may be recommended for some women with severe symptoms from menopause, or women who are at very high risk for osteoporosis or heart disease. One of these supplemental drugs might be androgen, a male hormone given with estrogen to relieve severe hot flashes.

HEALTHY LIFESTYLE

In addition to taking HRT, there are other things that can help women adjust to the changes in life during menopause. Eating healthy foods and getting regular exercise will also help to decrease bone loss and maintain healthy heart muscle.

CALLING YOUR HEALTH CARE PROVIDER

It is important to have regular checkups with your health care provider when taking HRT. If you have continual vaginal bleeding during HRT or other unusual symptoms, call your health care provider.