What are the risks of Hormone Replacement Therapy?
By Dr Ellie Cannon • 17, Mar 2025
The current thinking from women’s health experts is that for most women, Hormone Replacement Therapy is safe and since it works very well, the risks – which are small for most women – are outweighed by the benefits.
Your life expectancy is unlikely to change because you use Hormone Replacement Therapy.
All medications come with risks and side effects, and Hormone Replacement Therapy (HRT) is no different. Your own personal thoughts on risk should be a significant part of your decision-making when it comes to HRT. And you can only do that when you have all the unbiased facts.
It’s also vital to understand that risks can change because science and knowledge evolve. As the body of science grows and the use of HRT increases, the research gets better and better, and perhaps more concrete. We can be more definitive when we say what is and isn’t a real risk as time moves on and more vital research is carried out.
It’s a complicated balancing act but this is why an individual approach to HRT is so important, because one size does not fit all, especially when talking about risk.
While you’re weighing up your potential risks from HRT, the other relevant health factors for you to think about are your:
Weight
Alcohol intake
Levels of exercise
Smoking history
Age
Other health problems, such as diabetes
Family history
You can’t sensibly judge risks from HRT without adding these factors into the mix – for example, alcohol intake has a more substantial effect on breast cancer risk than HRT.
Breast cancer
This was always one of the big historical worries about HRT, which isn’t surprising. Breast cancer can be related to changes in female hormones, so it’s scientifically expected that hormonal treatments such as the contraceptive pill or HRT may increase breast cancer risk.
Also, breast cancer is common and talked about a lot, so we are understandably more concerned about it than other health problems due to inherent bias.
When thinking about breast cancer, there are also other factors, such as your weight, your ethnic background and your family history, which are as relevant to this discussion as your use of HRT.
Taking oestrogen-only HRT does not increase your risk of getting or dying from breast cancer. The official guidance from the large scientific trials shows us that having this type of HRT has little or no effect on someone’s risk of breast cancer.
Vaginal oestrogen does not affect your breast cancer risk.
Combined HRT can be linked to an increased risk of breast cancer. The important thing to know is that this is linked to how long you take HRT and that the risk reduces again after you stop HRT. This is one of the reasons we always suggest you use the lowest dose of HRT for the shortest time.
The increased chances of breast cancer are considered low in scientific and statistical terms, and the only way to explain these accurately and honestly is to look at number comparisons (see below).
In the UK, about 2 per cent of breast cancer cases are thought to be linked to the use of HRT.
Interestingly, if micronised progesterone or dydrogesterone is used for combined HRT, the risks are considered lower – the scientific evidence for this is still being gathered.
After stopping HRT, your risk will go back down, but this reduction can take years – it isn’t immediate and will take longer the longer you were on HRT.
If we have a group of typical women who take HRT for five years from the age of 50, how does the risk of breast cancer compare to the same women not taking HRT?
After 20 years, this is how many would develop breast cancer:
On oestrogen-only HRT – 7 out of 100 women would develop breast cancer rather than 6.5 out of 100 if they were not on HRT
On sequential/cyclical HRT – 7 out of 100 women would develop breast cancer rather than 6 out of 100 if they were not on HRT.
On continuous combined HRT – 8 out of 100 women would develop breast cancer rather than 6 out of 100 if they were not on HRT.
To put this in context, the risk of developing cancer from HRT is still less than the risk of developing cancer from being obese or from drinking alcohol every day.
Other cancers
In terms of other cancers, the picture regarding HRT is generally reassuring. HRT appears to reduce the risk of developing colorectal cancer and has no effect on developing cervical cancer.
For ovarian cancer, the science suggests there is a very small increase in the risk of getting some types of ovarian cancer from taking either oestrogen-only or combined HRT. This is the case whether you take tablets or use transdermal treatments. Experts currently believe this to be small enough not to outweigh the benefits of taking HRT in women who find it helpful for alleviating their menopausal symptoms. It is believed for every 1000 users of HRT, there would be one extra case of ovarian cancer.
If your family is affected by ovarian cancer or carries genes that may increase your chances of developing it, you must discuss this during your HRT conversations.
Blood Clots
Blood clots have always been a health concern in HRT. The oestrogen in the HRT is the problem since it can increase your chance of forming a clot. The same issue arises with the contraceptive pill, also due to the oestrogen in it.
Having a blood clot is dangerous. Our blood is supposed to travel freely in our blood vessels. A clot forming causes a blockage and cuts off vital blood supply. This is very serious, causing pain, swelling and organ damage, for example in the lungs, brain or heart. It can also occur in the legs, and this is what we call a DVT – a deep vein thrombosis – where a clot forms and the leg dangerously swells.
Some people are more at risk of blood clots, for example if you have had a blood clot before or are known to have a blood clotting disorder. Women who are overweight or smokers are also more at risk of blood clots. It is really important to discuss any relevant blood clotting history from your family history with your doctor before starting HRT.
Taking HRT orally increases the risk of developing a blood clot, particularly in your first year of taking it. This increase could be as much as four times the normal risk, but it’s not all bad news:
The chances of having a blood clot before you start HRT are very low, so even if they are increased, your chances as an individual still remain low.
None of the transdermal types of HRT increases the risk of blood clotting, so someone concerned about clotting risk would opt for patches or similar from the outset. It appears that when the oestrogen is taken into the body through the skin, it does not cause the increased clotting risks.
This is only the case if the treatments are used at standard mainstream doses – using unregulated, overly high doses of oestrogen in any form will increase the risk of blood clots.
Micronised progesterone and dydrogesterone give less risk of blood clots than other progestogens.
So before you start HRT, you should be thinking about your background risk factors for blood clotting. If someone is affected by obesity or at risk for other reasons, transdermal HRT or micronised progesterone would be a first option, as they are safer in this regard.
Heart Disease
Heart disease is sometimes called coronary heart disease or cardiovascular disease or is referred to as different conditions such as angina or a heart attack. It is caused by the narrowing or ‘furring’ of the arteries, which reduces the amount of blood that can get to the heart. The worst-case scenario is that the blood is completely blocked from getting to the heart, and this is called a heart attack.
There are many risk factors for heart disease, including weight, exercise levels, smoking, high cholesterol, high blood pressure and type 2 diabetes. There are also risk factors you can’t control, such as age, family history and ethnic background.
Heart disease risk does not increase with the use of combined or oestrogen-only HRT.
Stroke
A stroke is when the blood supply to part of the brain is cut off. This is commonly due to a blood clot but may also be the result of bleeding in the brain. Of course, it is a very serious health condition and can lead to irreversible damage.
The risk of stroke from HRT is something that science has gone backwards and forwards on. However, it is not surprising to me that currently, the advice on stroke risk from HRT is very similar to the advice on blood clots.
It’s important to remember that for all women under the age of 60, the risk of stroke is very low, so even if there is an increase, you are still at a low risk.
As with blood clots, it appears that taking HRT tablets does slightly increase the risk of having a stroke, and this increase is related to how much you take – the higher the dose of oestrogen, the higher your risk. Likewise, the longer you take it, the higher the risk.
The risk of stroke from taking oral HRT is higher if you start it when you are older and is also greater for Black women.
Once again, using HRT transdermally with patches and other skin-based regimes does not cause this risk and, again, the type of progestogen you use is important:
None of the transdermal types of HRT increase the risk of stroke, so someone concerned about this risk or who is aged over 60 would opt for patches or similar from the outset.
Micronised progesterone and dydrogesterone give less risk of stroke than other progestogens.
Dementia
Dementia is something we are all afraid of, and as yet, we don’t know how to prevent it or cure it.
Since more women than men seem to get dementia, there is thought to be a possible link to the female hormones, and notably oestrogen, the main one in HRT
Some medical studies have actually shown that being on oestrogen or combined HRT increases the risk of developing dementia, but other studies disagree with this and suggest it reduces the risk. It’s confusing and the science is still growing.
Since we know that HRT helps to reduce menopausal brain fog and improves concentration, some people made the leap that it must, therefore, help to prevent dementia. But that isn’t the case. In fact, it may be the case that women experiencing brain fog as an early symptom of dementia wrongly assume it is menopause-related and start HRT. This could lead to the wrong assumption that more women on HRT get dementia than otherwise.
Large scientific studies have shown HRT to be a risk, but other studies have that it is protective when it comes to dementia
So, in truth, no one is sure about this stage. What we do know, if we look at it pragmatically, is that HRT can improve your quality of life around menopause and allow you to do things like exercising, working, and socialising, which are known to keep memory problems at bay. For now, that’s all we can say for certain about dementia risk and HRT. It might be allowing you to do the things that are really important in helping prevent dementia.
If you found this post helpful, visit our Menopause Health Check to learn more about how our expert GPs can help you stay on top of your health.
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