Purpose of review: Venous thromboembolism (VTE) is a main harmful effect of oral estrogen therapy among postmenopausal women. Transdermal estrogens may be safer but early results need to be confirmed. This review provides a summary of the most recent findings regarding the VTE risk among oral versus transdermal estrogens users.
Recent findings: Since 2008, we identified five relevant observational studies. Among them, two large cohort studies confirmed that oral but not transdermal estrogens were associated with VTE risk among postmenopausal women. In an updated meta-analysis of current data, pooled risk ratios for VTE were 1.9 [95% confidence interval (CI) 1.3-2.3] and 1.0 (95% CI 0.9-1.1) among oral and transdermal estrogens users, respectively. In addition, one recent cohort study showed that transdermal estrogens did not confer an excess risk of recurrent VTE among postmenopausal women with a history of VTE. The difference in VTE risk between oral and transdermal estrogen users is supported by biological data. Whereas oral estrogens can increase thrombin generation and induce a resistance to activated protein C, transdermal estrogens have minimal effects on hemostatic variables.
Summary: Transdermal estrogens may improve substantially the benefit/risk ratio of postmenopausal hormone therapy and should be considered as a safer option, especially for women at high risk for VTE.