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An estrogen (E) is a type of medication which is used most commonly in hormonal birth control and menopausal hormone therapy, and as part of feminizing hormone therapy for transgender women. They can also be used in the treatment of hormone-sensitive cancers like breast cancer and prostate cancer and for various other indications. Estrogens are used alone or in combination with progestogens. They are available in a wide variety of formulations and for use by many different routes of administration. Examples of estrogens include bioidentical estradiol, natural conjugated estrogens, synthetic steroidal estrogens like ethinylestradiol, and synthetic nonsteroidal estrogens like diethylstilbestrol. Estrogens are one of three types of sex hormone agonists, the others being androgens/anabolic steroids like testosterone and progestogens like progesterone.
Side effects of estrogens include breast tenderness, breast enlargement, headache, nausea, and edema among others. Other side effects of estrogens include an increased risk of blood clots, cardiovascular disease, and, when combined with most progestogens, breast cancer. In men, estrogens can cause breast development, feminization, infertility, low testosterone levels, and sexual dysfunction among others.