Estrogen-Only Hormone Therapy Carries Lower Risk of Blood Clot Formation

Hormone replacement therapy (HRT) is used to treat a wide range of conditions in women. Recent evidence has come to light which suggests that estrogen-only hormone replacement therapy carries a significantly lower risk of venous thromboembolism (VTE) as compared to the combined estrogen-progesterone hormone therapy.

The study was carried out in over 800 Swedish women and was subsequently published online in Menopause, the journal of The North American Menopause Society. The 800 case subjects who had VTE were matched against 900 control subjects who took no hormones.

The basic aim of the study was to find out whether  lower doses or transdermal (through the skin) doses of estrogen-only or combined estrogen-progesterone hormone therapy carry lower risk of VTE or not.

Lower Risk of VTE with Estrogen-Only Therapy

The researchers came up with quite astonishing figures. The risk of developing VTE was almost 1.72 times higher in women taking hormone therapy as compared to those who took no hormones at all. The women taking combined HRT were found to have three times more risk of VTE when compared with women who were given no hormones.

Women who received estrogen-only HRT, mainly because they had undergone hysterectomy and did not need progesterone at all, were found to have the lowest risk of developing VTE- 1.31 times higher risk compared to the women who received no hormone therapy.

Women who received combined estrogen-progesterone therapy were discovered to carry a twofold higher risk of developing VTE when weighed against women receiving estrogen-only hormone therapy.

Route of Administration of Estrogens Makes A Difference 

The study came up with the astounding discovery about the route of administration of estrogens. It was found that there was no increased risk of VTE in women who used transdermal estrogen in the form of patches, either alone or in combination with progesterone.  

Women, who used vaginal estrogens to combat vaginal dryness and other symptoms of menopause, were also found to carry no added risk of VTE. This is thought to be due to the fact that the absorption of vaginally administered estrogens into the blood stream is relatively less which is why these estrogens result in the same effects as seen in women who received no hormones.

The Future Prospects

The question whether or not the dose and route of administration of hormone therapy in women makes a difference, has frequently gone unanswered. This study has helped resolve this issue and has helped direct the future studies towards finding hormone therapies that impart the maximum benefit with a significant reduction in their side effects, particularly VTE which proves to be fatal in most of the women.  

This study has also helped find the optimally beneficial route of administration which will benefit women in the long run by reducing the risk of blood clot formation.

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According to NAMS Executive Director JoAnn V. Pinkerton, MD, NCMP, this study has helped understand how transdermal estrogen therapy is safer than the oral one. It has also effectively established that various estrogen or progestogen combinations carry different risks.These findings will have a great impact in developing safe therapies via transdermal or vaginal route for women who are at high risk of blood clot formation.