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HomeMedicineInternal MedicineDoes hormone replacement therapy increase the risk of blood clots?

Does hormone replacement therapy increase the risk of blood clots?

Researchers from the UK conducted a large study of women on different types of hormone replacement therapy to see if it increased the risk of blood clots.

Hormone replacement therapy is prescribed for women going through menopause to help relieve some of the effects of this process, including night sweats, hot flashes, and mood swings.

Recent guidelines from the UK-based National Institute for Health and Care Excellence (NICE) indicated that there is a lack of information about the risks and benefits of hormone replacement therapy.

Different types of hormone replacement therapy

Hormone replacement therapy can come in several different forms, and each type aims to replace the hormones that the body is no longer producing as it goes through menopause.

It can be based on estrogen alone, or sometimes combined with the hormone progesterone. The formulation differs also, and it can be taken in tablet form, gel, cream or patch.

Previous research has indicated that there is an increased risk of blood clots (venous thromboembolism) in women who take hormone replacement therapy. Blood clots can travel to different parts of the body where they can lodge and cause a range of problems from mild to life-threatening.

However, the NICE report indicated that there is not enough data on the subject for doctors to be able to make reliable recommendations on taking this therapy.

To address this gap in knowledge, researchers from the UK looked back at the medical records of thousands of women who had suffered from blood clots. They published their findings in the British Medical Journal.

Researchers compared the medical records of more than 80,000 women who had suffered from blood clots, with records from similar of a similar age but no history of blood clots.

In particular, they looked at whether the women had taken hormone replacement therapy and in what form it had been prescribed eg tablets, gels, creams or patches.

Hormone replacement therapy in tablet form was associated with higher likelihood of  blood clots

The researchers found that the women who had blood clots were more likely to have taken hormone replacement therapy. Once the data was teased apart further and analysed, the researchers found that women who took tablets for hormone replacement therapy were twice as likely to get blood clots as women who did not.

The way in which the hormone had been made also affected the likelihood of blood clots. However, there was no increased risk in women who used the patch, cream or gel formulations.

The researchers conclude that these are the safest types of hormone replacement therapy.

Interestingly, the women who were studied did not commonly use the gels, creams and patches.

The researchers discuss that their findings are particularly important to women and their results could be helpful for new guidelines to be developed to help women and their healthcare providers make informed choices about treatment.

Written by Nicola Cribb, VetMB DVSc Dip.ACVS


  1. Vinogradova Y, Coupland C, Hippisley-Cox J. Use of hormone replacement therapy and risk of venous thromboembolism: nested case-control studies using the QResearch and CPRD databases. Bmj. 2018;364:k4810. doi:10.1136/bmj.k4810.
  2. Eurekalert. The global source for science news. Last accessed: February 8, 2019.


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Nicola Cribb
Nicola Cribb
Nicola obtained her Veterinary and Master’s degrees from the University of Cambridge, UK, and Doctor of Veterinary Science from the University of Guelph, Canada. She is board-certified in surgery and has research interests in minimally-invasive surgery. She has worked in a clinical setting, as well as research and teaching disciplines for the past 16 years at the University of Guelph, where she is currently Adjunct Faculty. She is a freelance medical writer and reviews, authors, and co-authors publications and reviews in scientific journals and books.


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