What are the risks in taking HRT?

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There has been a lot of media attention to the risks
of taking HRT. This was after the results of some big studies about HRT
were published between 2002 and 2004. These were the Women's Health
Initiative Study in the USA and the Million Women Study in the UK.
These studies raised concerns over the safety of HRT, particularly over
a possible increased risk of breast cancer with HRT and also a possible
increased risk of heart disease. However, it is important that the
results of the studies are looked at carefully. HRT does
increase your risk of developing certain problems but this increase in
risk is very small in most cases. The risks of taking HRT are discussed
below.

Venous thrombo-embolism

This is a blood clot
that can cause a deep vein thrombosis (DVT). In some cases the clot may
travel to the lung and cause a pulmonary embolism (PE). Together, DVT
and PE are known as venous thrombo-embolism. The risk seems to be
higher with combined HRT compared to oestrogen-only HRT and the risk is
also higher in the first year that you take HRT. This risk seems to be
slightly lower if you use HRT patches rather than HRT tablets taken by
mouth.

In women aged 50-59 years, over a five-year period:

About 5 in 1,000 women who do not use HRT are likely to develop a blood clot.
In 1,000 women taking oestrogen-only HRT for five years, there will be an extra two women who will develop a blood clot.
In 1,000 women taking combined HRT for five years, there will be an extra seven women who will develop a blood clot.

In women aged 60-69, over a five-year period:

About 8 in 1,000 women who do not use HRT are likely to develop a blood clot.
In 1,000 women taking oestrogen-only HRT for five years, there will be an extra two women who will have a blood clot.
In 1,000 women taking combined HRT for five years, there will be an extra 10 women who will have a blood clot.

(See separate leaflets called 'Deep Vein Thrombosis' and 'Pulmonary Embolism'
for further details.) You should see a doctor urgently if you develop a
red, swollen or painful leg, or have shortness of breath and/or sharp
pains in your chest.

Breast cancer

You may have a small increased
risk of breast cancer if you take HRT. Combined (oestrogen and
progesterone) HRT has a higher risk than oestrogen-only HRT. This risk
increases the longer you have used HRT. When you have been off HRT for
five years, you have the same risk of breast cancer as someone who has
not taken HRT.

In women aged 50-59 years:

About 10 per 1,000 women who do not use HRT are likely to develop breast cancer over a five year period.
In 1,000 women who are taking oestrogen-only HRT for five years,
there will be an extra two women who will develop breast cancer.
In 1,000 women taking combined HRT for five years, there will be an extra six women who will develop breast cancer.
About 20 per 1,000 women who do not use HRT are likely to develop breast cancer over a 10-year period.
In 1,000 women who are taking oestrogen-only HRT for 10 years, there will be an extra six women who will develop breast cancer.
In 1,000 women taking combined HRT for 10 years, there will be an extra 24 women who will develop breast cancer.

In women aged 60-69 years:

About 15 per 1,000 women who do not use HRT are likely to develop breast cancer over a 5-year period.
In 1,000 women who are taking oestrogen-only HRT for 5 years, there will be an extra 3 women who will develop breast cancer.
In 1,000 women who are taking combined HRT for 5 years, there will be an extra 9 women who will develop breast cancer.
About 30 per 1,000 women who do not use HRT are likely to develop breast cancer over a 10-year period.
In 1,000 women who are taking oestrogen-only HRT for 10 years, there will be an extra 9 women who will develop breast cancer.
In 1,000 women who are taking combined HRT for 10 years, there will be an extra 36 women who will develop breast cancer.

Stroke

There is a small increased risk with both oestrogen-only and combined HRT.

In women aged 50-59 years:

About 4 in 1,000 women who do not take HRT will have a stroke over a five year period.
In 1,000 women who take oestrogen-only HRT for five years, there will be an extra one woman per 1,000 who will have a stroke.
In 1,000 women who take combined HRT for five years, there will be an extra one woman per 1,000 who will have a stroke.

In women aged 60-69 years:

About 9 in 1,000 women who do not take HRT will have a stroke over a five year period.
In 1,000 women taking oestrogen-only HRT for five years, there will be an extra three women per 1,000 who will have a stroke.
In 1,000 women taking combined HRT for five years, there will be an extra three women per 1,000 who will have a stroke.