What are the benefits and risks of long-term hormone therapy?

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Hormone therapy can help ease symptoms of menopause. But it is associated with a lot of serious risks if used over the long term. Although the treatment lowers the risk of bone fractures, it increases the risk of cardiovascular disease (heart and blood vessel problems) and breast cancer.

Women’s hormone levels change during the time leading up to menopause (known as perimenopause). This can lead to hot flashes, sweats and mood swings. Some women have such severe symptoms that they start looking for treatments. One treatment option is hormone therapy with estrogen, or with a combination of estrogen and progestin. Combination drugs are generally used because estrogen can lead to growths in the lining of the womb when used alone. So estrogen-only medications are only suitable for women who have had a hysterectomy (surgery to remove their womb).

In the past it was thought that taking hormones for a long time after menopause can protect women from serious diseases. But this assumption turned out to be wrong. On the contrary: It is now clear that this treatment actually increases the risk of certain serious diseases. These include:

Pros and cons of hormone therapy

A summary of studies has shown that estrogen therapy and treatment with a combination of estrogen and progestin both have a lot of disadvantages – the longer the treatment lasts, the more disadvantages.

The following tables show how common certain medical conditions are in women who have long-term hormone therapy after menopause. The data was mainly taken from a large U.S. study called the "Women's Health Initiative Study" (see below).

Advantages of hormone therapy

The research suggests that long-term hormone therapy can prevent bone fractures. Some analyses of the studies also suggest that hormone therapy could lower the risk of bowel cancer somewhat.

Regarding bone fractures, the following advantage was found after eight years: Bone fractures occurred in

  • 126 out of 1,000 women who had treatment with estrogen and progestin, and in
  • 154 out of 1,000 women who didn't have hormone therapy (were given a placebo).

So the treatment prevents bone fractures in 28 out of 1,000 women.

Disadvantages of hormone therapy

The risk of various medical problems already increased after one year, and then continued to increase after that. The following disadvantages were found in women who had treatment with estrogen and progestin:

Table: Frequency of thromboembolism, stroke and breast cancer – with and without estrogen and progestin treatment.
Health problem and duration of treatment Frequency when taking estrogen and progestin Frequency without hormone therapy (placebo) Disadvantage in

Thromboembolism

8 years

25 out of 1,000 women 15 out of 1,000 women 10 out of 1,000 women

Stroke

8 years

19 out of 1,000 women 14 out of 1,000 women 5 out of 1,000 women

Breast cancer

8 years

33 out of 1,000 women 26 out of 1,000 women 7 out of 1,000 women

The risk of heart attacks might increase a little too. If women take a combination of estrogen and progestin for longer than five years, their risk of breast cancer will probably stay higher even after they stop hormone therapy. Also, one analysis showed that women who have long-term hormone therapy are more likely to develop dementia.

Women who only took estrogen didn't have a higher risk of breast cancer and heart attacks. They had a similar risk of stroke and thromboembolism as women who took a combination of estrogen and progestin did:

Table: Frequency of stroke and thromboembolism – with and without estrogen therapy
Health problem and duration of treatment Frequency when taking estrogen Frequency without hormone therapy (placebo) Disadvantage in

Stroke

7 years

32 out of 1,000 women 24 out of 1,000 women out of 1,000 women

Thromboembolism

7 years

21 out of 1,000 women 16 out of 1,000 women 5 out of 1,000 women

Weighing the pros and cons

  • Based on current research findings, it's not advisable to take hormones as a preventive measure or over a long period of time.
  • If you have severe menopause-related problems, it's a good idea to carefully weigh the pros and cons of hormone therapy together with your doctor.
  • If you decide to use hormones, the treatment should be as short as possible, using the lowest dose possible.

About the research

Researchers from the Cochrane Collaboration wanted to summarize what is known about long-term hormone therapy. To do that, they looked for and analyzed all of the studies in which women had taken hormones or a dummy drug (placebo) every day for at least a year. They found a total of 22 studies involving more than 43,000 women. They were about 60 years old on average, so most of them had already gone through menopause.

The biggest study, known as the "Women’s Health Initiative Study (WHI)," involved about 27,000 participants. In that study, one group of women took either estrogen alone or a combination of estrogen and progestin. The other group took a dummy drug (a placebo).

The treatment in the study was stopped after about 5 to 7 years, before it was meant to stop, as it became clear that it had more disadvantages than advantages. But the researchers stayed in touch with the women in the study for several years afterwards, in order to find out whether the treatment had any late effects.