A 10-year study was conducted to compare the effects of transdermal (skin patches) and oral estrogen therapy on risk for cardiovascular events. The study looked at over 5000 women with the average age of 55. They excluded women who had a prior history of blood clots or coronary heart disease or who filled a prescription for any progestin, estrogen injection, gel or spray or a contraceptive pill during the study period or 6 months prior to starting the transdermal or oral estrogen.
Participants were exposed to an average of 16 months of estrogen therapy. Results showed lower venous thromboembolism (blood clots) and strokes among transdermal estrogen users. This is consistent with numerous observational studies. This is biologically plausible with the fact that transdermal application does not elevate liver production of clotting proteins. This supports the view that transdermal estrogen is indeed safer than the oral route with respect to blood clots. The European menopause Society (Maturitas 2011; 69:195) and the Endocrine Society (J Clin Endocrine Metab 2015; 100:3975) both recommend the transdermal formulation for menopausal women at risk for blood clots. This includes women with a previous history of blood clots, smokers and those who are obese).
This information may also explain the statistically significant increase in venous thromboembolism in women that participated in the Women’s Health Initiative Study launched in 1991 who were using oral Prempro (oral estrogen and progestin). That study was primarily looking at the risks and benefits of that particular drug vs hormone replacement therapy. As you can see, not all estrogens are alike nor do they get metabolized the same in the body. Personalizing a women’s hormone therapy is important. Discussing the types of estrogen and explaining the risks and benefits of route of administration is vital in helping women make the right choice that is effective and safe for them.
Reference: Simon JA et al. Venous thromboembolism and cardiovascular disease complications in menopausal women using transdermal versus oral estrogen therapy. Menopause 2016 June; 23:600.
Canonico M and Scarabin P. Y. Oral versus transdermal estrogens and venous thromboembolism in postmenopausal women: What is new since 2003? Menopause 2016 June; 23:587.