Study: Oral HRT Doubles Blood Clot Risk

Women who take the oral form of hormone replacement therapy more than double their risk of developing a blood clot, a team of French researchers said.

The review, published in the British Medical Journal, also said that HRT via skin patches may cause fewer blood clots than HRT given orally,

A team led by Marianne Canonico of the Paul Brousse Hospital in Paris reviewed data from eight observational studies and nine randomized controlled trials.

The reviewers said they found that women taking the oral form of the drug were between two and three times more likely to develop a blood clot, and that the risk was significantly higher during the first year of treatment.

Past treatment was not associated with increased risk. If a woman was overweight or genetically pre-disposed towards suffering from blood clots then the risk increased further.

HRT given in patch form showed no significant increase in the risk of venous thromboembolism — blood clot in the vein which can be fatal. However, the authors warn that the results should be treated with caution as the data is from observational studies — no trials have yet investigated the effects of estrogen patches on the risk of venous thromboembolism.