It is well known that women taking oestrogen replacement therapy are at an increased risk of developing venous thromboembolism (VTE) - a potentially-fatal type of cardiovascular disease where blood clots develop in deep veins, such as the leg or pelvis, or in arteries in the heart and lungs.

However, results of a six-year study have found that the risk of postmenopausal women developing VTE may decrease when the oestrogen is delivered through a transdermal patch, rather than taken orally in pill form.

"Oral, but not transdermal oestrogen is associated with an increased VTE risk," concluded the French researchers.

These findings may therefore have implications for the way this drug is formulated and delivered to women in the future, as it comes at a time when there are growing concerns over the risks compared to the benefits of taking oestrogen replacement therapy, which not only increases the risk of VTE, but is also associated with an increased incidence of biliary disease, endometrial and breast cancer, as well as raised serum triglyceride levels.

The study, called ESTHER (estrogen and thromboembolism risk), was published in the 20 February issue of the journal Circulation.