Estradiol hormone replacement therapy (HRT) patches. Box containing transdermal patches of the hormone replacement drug Estradiol. HRT is used to treat menopause symptoms by replacing female sex hormones. Estradiol contains estradiol hemihydrate, a naturally occurring form of oestrogen. HRT can also help to prevent osteoporosis. However, side-effects include an increased risk of thrombosis and some forms of cancer.