Hormone replacement therapy (HRT) tablets taken orally are associated with a small but serious risk of blood clots, known as venous thromboembolism (VTE), a new study has found.
However, the study showed that skin-applied treatments – called transdermal – and one oral treatment, called tibolone, showed no associated risks of VTEs.
The study also found that oral HRT remained the preferred choice of treatment by women.
HRT, now known more commonly as menopause hormone therapy (MHT), is used to treat symptoms such as hot flushes and night sweats, which severely affect around 20% of menopausal women. HRT is effective in managing menopausal symptoms, but has been linked to VTE, a rare but serious risk.
VTE is a disease that includes deep vein thrombosis (DVT) and pulmonary embolism (PE).
Despite past studies confirming the increased risk of VTE as a result of HRT, none until now have provided comparisons between the different types of hormone therapies.
This study in the United Kingdom, which was published in the British Medical Journal, is the first to analyse the risk of VTE across the range of oral and transdermal HRT products.
This observational – or community-based – study compared prescription records of more than 80,000 women aged from 40 to 79 who were diagnosed with VTEs between 1998 and 2017, with a control group of more than 390,000 women who did not have VTEs.
Of those 80,000 women diagnosed with VTE, almost 6000 – a little over 7% of them – had been on HRT. But of those 7%, 85% of them had been on oral therapy.
Of the control group of more than 390,000 without VTEs, 5.5% of those had used HRT.
Relevant factors such as lifestyle, family history and underlying conditions were taken in to account, giving researchers the clearest picture to date of HRT product and VTE risk.
Researchers found a zero risk of VTE with transdermal treatments such as gels, creams and patches and the oral tibolone. However, VTE risk was associated with an extra nine cases per 10,000 women per year for oral preparations. Oral preparations using conjugated equine oestrogen was associated with the highest risk of blood clot. The higher the dose, the higher the risk.
"I think this study has been very important in highlighting the differences between the oral and transdermal products," says gynaecologist and Jean Hailes for Women's Health Medical Director, Dr Elizabeth Farrell.
"We've always suggested that the safest therapies are a combination of transdermal and oral progesterone, or only transdermals."
Dr Farrell says that while the study confirms that transdermal treatments are the safest type of HRT, women should feel reassured that blood clots are a rare complication, regardless of the type of oral HRT used.
"Women should not be alarmed by the latest study," she says. "It confirms what we already know from other studies.
"Within 10 years of the final menstrual period, hormone replacement therapy is a very safe therapy for most women."
Women who have concerns are advised to talk to their doctor to discuss their individual needs. Read more about managing menopausal symptoms.