The route of administration of estrogens may have implications for adverse effects. For example, transdermal estrogen bypasses the liver so avoids the liver effects that occur with use of oral medications, and has slightly different effects on triglycerides and cholesterol than oral estrogens. Also, the specific type of estrogen is of importance, with transdermal 17-beta estradiol not having the increased risk of venous thromboembolism seen with ethinyl estradiol.
Some patch systems for hormone replacement therapy consist of a continuous estrogen patch in addition to an intermittent patch containing a progestogen (progestin), in order to decrease disturbances in the endometrium of the uterus. The combination of estrogen and progestogen make them somewhat similar to the contraceptive patch. For example, Sequidot consists of a continuous estradiol patch in addition to a norethisterone patch that is worn 14 days in each 28 day cycle.