A study suggests that women who take hormone replacement in the form of patches are less likely to have blood clots that those taking oral hormones.

Blood clotting is a known side effect of hormone replacement therapy. The estrogen component affects blood coagulation and makes women more prone to venous blood clots in the leg. Researchers in France have carried out a multi-center study, comparing women taking estrogen in transdermal patch form with those taking an oral version.

In a group of 155 women with an episode of venous thrombosis (blood clot) 21 per cent were on oral estrogen, compared to just seven per cent of control women who had not had a blood clot. But 19 per cent of the women with clots were using transdermal estrogen, compared to 24 per cent of those in the control group. Further analysis suggested that women on oral estrogen were three times more likely to develop a clot compared to women on transdermal estrogen or those not taking estrogen at all. The study suggests that the patch form of estrogen is safer than the oral version - at least when it comes to avoiding unwanted blood clots.

Source

The Lancet 9th August 2003