The estrogen patch is a elivery system for estradiol, which is used as hormone replacement therapy to treat the problems of menopause, such as hot flashes and vaginal dryness, and to prevent osteoporosis. The estrogen is given transdermally rather than via oral tablets, meaning that the estrogen patch carries similar risks and benefits that conventional forms of estrogen-only hormone replacement therapy have, but there are also important differences. 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.