Researchers at Vermont University, USA, have found that all women on HRT containing oestrogen and progestin have double the risk of developing venous thrombosis (blood clots). Older or obese women have an even higher risk.
You can read about this study in the Journal of the American Medical Association.
Researchers looked at 16,608 postmenopausal women aged 50-79.
The scientists found that 167 women on HRT with oestrogen and progestin developed venous thrombosis, compared to 76 women who were on a placebo.
According to the researchers, the likelihood of women developing a blood clot increased as follows:
Aged 60-69: 4.3 times higher risk
Aged 70 or more: 7.5 times higher risk
Overweight women: 3.8 times higher risk
Obese women: 5.6 times higher risk
Over a ten-year period, combined HRT causes an extra 18 cases of blood clots (venous thrombosis) per thousand women, said the researchers.
Experts say this information should not put women off using combined HRT. Rather, women should talk to their doctors and weigh up the pros and the cons. In many cases combined HRT is still the best treatment.