Taking HRT pills to cope with the menopause doubles the risk of dangerous blood clots, research has found.
A major study has shown that those who take hormone replacement drugs in pill form are more likely to suffer pulmonary embolism or deep vein thrombosis.
Both conditions can be fatal or require the amputation of a leg.
Researchers from the University of Nottingham who studied 80,000 British women found the risk increased only with tablets – patches, gels or creams did not increase the incidence of blood clots.
Women take HRT to cope with menopause symptoms including depression, hot flushes and night sweats. It works by replacing the female hormone oestrogen as the body stops producing it. Around 80 per cent of those who use it take the tablet form.
The new findings, published in the British Medical Journal, show that equine oestrogen tablets, such as the Premarin brand, carry a higher risk than synthetic oestrogen.
Researcher Dr Yana Vinogradova, of the Nottingham School of Medicine, said: ‘Different tablets are associated with different risks of developing blood clots.’
She said the lower risk with patches or gels had been known about for some time so it was surprising that only 20% of women took HRT in that way.
Researchers stress that the absolute risk remains small. They found that for every 10,000 women who take HRT pills, there are just nine extra cases of clots every year.
But in 2015, health watchdog Nice issued new guidance advising GPs to start offering the drug to more women, saying the cancer fears had been overblown.
Out of 10,000 taking HRT for five years, for example, there would be just 60 extra cases of breast cancer and 15 of ovarian cancer.
Professor Helen Stokes-Lampard, of the Royal College of GPs, said HRT was the only effective treatment for menopause symptoms.
‘Best practice is to prescribe the lowest possible dose of HRT for the shortest possible time, and so specific products and formulations of HRT are only initiated after a comprehensive discussion.’
Dr Channa Jayasena, of Imperial College London, added: ‘We know that HRT has important benefits to alleviate menopausal symptoms. All drugs have side effects.
‘This helpful study allows us to see which types of HRT have the highest and lowest risk. HRT patches have the lowest risk and should be first choice for older women, for whom blood clot risk is highest.’
She said the study reassured women that blood clots were still an uncommon HRT complication.