When deciding whether to have hormone replacement therapy (HRT), it's important to understand the risks.

It's also important to consider HRT as only 1 of a range of options to improve menopausal and postmenopausal health and wellbeing.

Many studies on HRT that have been published over the past 15 years highlight the potential risks. As a result, some women and doctors have been reluctant to use HRT.

But more recent evidence says that the risks of HRT are small and are usually outweighed by the benefits.

Breast cancer

Women who take HRT for more than 1 year have a higher risk of breast cancer than women who never use HRT. The risk is linked to all types of HRT except vaginal oestrogen.

For women in their 40s and 50s who take HRT for 5 years there would be:

  • 1 extra case for every 200 women taking oestrogen-only HRT
  • 1 extra case for every 70 women taking cyclical HRT
  • 1 extra case for every 50 women taking continuous HRT

The number of extra cases is thought to double among women who take these types of HRT for 10 years.

Research shows that the increased risk of breast cancer falls after you stop taking HRT, but some increased risk remains for more than 10 years compared to women who have never used HRT.

If you take it for less than 1 year, there is little or no increased risk of breast cancer.

Because of the risk of breast cancer, it's especially important to attend all your breast cancer screening appointments if you're taking HRT.

Ovarian cancer

Studies looking at whether HRT increases your risk of ovarian cancer have so far had conflicting results.

It's thought that if there is any increase in cases of ovarian cancer among women taking HRT, the increase is very small.

A recent study found that for every 1,000 women taking HRT for 5 years, there will be 1 extra case of ovarian cancer.

Any increased risk of ovarian cancer is thought to decrease once you stop taking HRT.

Womb cancer

Oestrogen-only HRT can increase the risk of womb cancer (also called uterine or endometrial cancer), which is why it's only used in women who do not have a womb (for example, because they've had a hysterectomy).

Taking combined HRT, particularly a course of continuous combined HRT (where you take both medicines without a regular break), largely eliminates this risk.

If you have a womb and you're taking HRT, it's important to take both medicines as advised by your doctor to avoid increasing your risk of womb cancer.

Blood clots

Blood clots can be serious if they become lodged in a blood vessel and block the flow of blood.

The evidence shows that:

  • taking HRT tablets can increase your risk of blood clots
  • there's no increased risk of blood clots from HRT patches or gels

It's thought the risk of developing a blood clot is 2 to 4 times higher than normal for women taking HRT tablets. But as the risk of menopausal women developing blood clots is usually very low, the overall risk from taking HRT tablets is still small.

It's estimated that for every 1,000 women taking HRT tablets for 7.5 years, fewer than 2 will develop a blood clot.

Heart disease and strokes

The evidence shows that:

  • HRT does not significantly increase the risk of cardiovascular disease (including heart disease and strokes) when started before 60 years of age
  • oestrogen-only HRT is associated with no, or reduced, risk of heart disease
  • combined HRT is associated with little or no increase in the risk of heart disease
  • taking oestrogen tablets is associated with a small increase in the risk of stroke, but the risk of stroke for women under age 60 is generally very low, so the overall risk is still small

Speak to a GP if you're taking HRT or are considering taking it and are worried about the risk of stroke or heart disease.