Danish study links oral hormone therapy to increased thrombosis risk

A large-scale Danish study published in the British Medical Journal has found that oral hormone replacement therapy (HRT) is associated with an increased risk of venous thrombosis. Researchers, led by Dr. Julie Berggreen from the Steno Diabetes Center Copenhagen, analyzed health and prescription data from over one million women aged 50 to 69 between 2003 and 2021.

The study indicates that women taking estrogen tablets face an average 60 percent higher risk of venous thrombosis compared to non-users, a finding that remained consistent regardless of dosage or duration of treatment. This increased risk is thought to occur because oral tablets pass through the liver, potentially stimulating the production of blood clotting factors.

However, the study provides reassurance regarding transdermal estrogen applications, such as patches, gels, and sprays. Because these methods bypass the liver, they appear to have little impact on blood clotting.

The research also highlighted cardiovascular risks associated with high-dose oral therapy. While doses up to 1 mg of estradiol daily did not show an increased risk of stroke or heart attack, taking more than 1 mg per day for over a year was linked to higher risks. After more than five years of such use, the risk of stroke and heart attack was approximately 80 percent higher than in women not using hormone therapy.