Hormone replacement therapy (HRT) patches that deliver low doses of estrogen via the skin pose a lower stroke risk than HRT in tablet form, new research suggests.

HRT, which is prescribed to women to ease the symptoms of menopause, such as hot flashes and a decrease in libido, has been linked to an increased risk of stroke in previous studies.

However, Canadian and German researchers have found that the risk of stroke was not increased with low-dose estrogen-only patches. However, the risk rose by 88 per cent when women used high-dose HRT patches.

"Our study suggests that the use of transdermal estrogen replacement therapy containing low doses of estrogen could be associated with a lower risk of stroke than the oral route of administration," write the authors.

Accessing the United Kingdom's General Practice Research Database, the researchers studied 870,000 women between the ages of 50 and 79 between January 1987 and October 2006. During that study period, 15,710 of the participants suffered their first stroke — an event that was then correlated to HRT use.

Taking HRT tablets was found to increase stroke risk by 25 to 30 per cent, regardless of whether they were estrogen-only or contained progesterone.

As well, those women who took HRT orally for a short time period (under a year) did not have an elevated risk of stroke, though women who took HRT tablets for over a year saw their risk rise by 35 per cent.

The study is published in the June 3 online issue of the British Medical Journal.