Hormone replacement therapy (HRT) tablets are associated
with a higher risk of venous thromboembolism (VTE), according to the findings
of a study published in the BMJ.
No increased risk was found for HRT skin patches, gels or
creams, yet the vast majority of women choosing HRT continue to be prescribed
The researchers say these findings provide important
information for women and their doctors to help them make the best treatment
Previous trials have shown increased risks of blood clots in
menopausal women using HRT, but there is a lack of information on risks
associated with different types of HRT.
So, Yana Vinogradova, a member of an epidemiological team at
the University of Nottingham led by Julia Hippisley-Cox, set out to assess the
association between VTE risk and all available types of HRT in the UK between
1998 and 2017.
Using two UK primary care databases (QResearch and CPRD),
they compared HRT prescription records of over 80 000 women aged 40-79 years
who developed blood clots (cases) with those of over 390 000 women who did not
Other relevant factors, such as lifestyle, family history of
blood clots, and underlying conditions linked to blood clots were taken into
Most HRT tablets were found to be associated with increased
VTE risk (9 extra cases per 10,000 women per year) compared with no HRT.
Tablets containing equine oestrogen, including single and
combined preparations, were consistently associated with higher risks than
tablets containing synthetic oestrogen.
Higher doses of oestrogen were also associated with higher
VTE risk. However, no increased VTE risk was found for skin patches, gels and
This is an observational study, and as such, can’t establish
cause, and the researchers point to some limitations that may have influenced
the results. Nevertheless, they say this study “has provided a more
detailed picture of the VTE risks for different HRT preparations and can help
clinicians and women make treatment choices.”
They suggest greater consideration should be given to
transdermal HRT, particularly for women already at an increased VTE risk and in
line with recent guidelines.
Y. Use of hormone replacement therapy and risk of venous thromboembolism:
nested case-control studies using the QResearch and CPRD databases. BMJ.
Published 9 January 2019. https://www.bmj.com/content/364/bmj.k4810