Hormone therapy for the menopause is associated with a slight increase in cardiovascular risk when taken orally

There are two ways of taking menopausal hormone therapy. One is by mouth, and the other is transdermal, through the skin. The results of this large study suggest that with oral menopausal oestrogen therapy, there is a small increased risk of blood clots in the legs, heart attacks and stroke. But if you’re using it transdermally (patches), then there’s no increased risk. This study confirms the findings of other studies around the world. 

The overall risk is fairly small. If you think about 10,000 women taking oral treatment, there would be nine extra cases of blood clots in the legs, six of stroke and only three of myocardial infarction with oral menopausal hormone treatment. The risk increases slightly as you go from 50 to 59 and 60 to 69 years-old, but overall the risk it’s pretty small. The risk is also higher in women on higher oral doses. Starting on a lower dose is always the safest strategy. 

Nine per 10,000 women is one in 1,000, so it’s uncommon. But taking oral medication is associated with more of these risks than having the treatment through the skin. 

This important study published in the leading journal, the British Medical Journal, provides an update on the risks of Menopause Hormone Therapy (MHT) and the risk of Thrombotic Disease (conditions in which an abnormal blood clot forms within a blood vessel or the heart and impedes blood flow).

It is a very large nation wide case control research study undertaken in Denmark, and specifically looking at associations between current use of menopausal hormone therapy and development of venous thromboembolism, ischaemic stroke, and myocardial infarction.

The results are largely supportive of previous studies and show that the current use of any oral menopausal hormone therapy was associated with an increased venous thromboembolism risk, whereas ischaemic stroke and myocardial infarction risk was only increased with oral high dose therapy used for more than one year.

Transdermal therapy was not associated with increased thrombotic rates regardless of regimen, active ingredients, dosage, and duration of use. This would suggest that the route of administration of MHT is important. Oral formulations that involve metabolism in the liver that are associated with clotting proteins that increase risk, whereas transdermal oestrogen largely avoids this effect and consequently has a lower thrombotic risk.

This study shows that although MHT is associated with a small increase in thrombotic risk, the absolute risk is low in most women and is outweighed by the benefits of menopause symptom relief. Risk assessment should be individualised, considering other health factors such as obesity, smoking, previous disease, age, and route of administration. Transdermal oestrogen generally carries a lower thrombotic risk than oral therapy.