Estradiol (medication)
Estradiol is also available in the U.S. in combination with progestogens for the treatment of menopausal symptoms and as a combined hormonal contraceptive:Estradiol and estradiol esters are also available in custom preparations from compounding pharmacies in the U.S. This includes subcutaneous pellet implants, which are not available in the United States as FDA-approved pharmaceutical drugs. In addition, topical creams that contain estradiol are generally regulated as cosmetics rather than as drugs in the U.S. and hence are also sold over-the-counter and may be purchased without a prescription on the Internet.
Pharmacodynamics of estradiol
Lower dosages and concentrations of estradiol can also significantly suppress gonadotropin secretion and testosterone levels in men and transgender women. A retrospective study of oral estradiol monotherapy in transgender women found that dosages of 1 to 8 mg/day increased mean estradiol levels to about 50 to 150 pg/mL and suppressed mean testosterone levels to about 120 to 10 ng/dL. However, there was high interindividual variability in the estradiol and testosterone levels achieved, and testosterone levels were insufficiently suppressed in many even at 8 mg/day. In another study, a dosage of 1 mg/day oral micronized estradiol in healthy older men, which increased circulating estradiol levels by a relatively high amount of 6-fold (to 159 pg/mL), estrone levels by 15-fold (to 386 pg/mL), and SHBG levels by 17%, was found to suppress total testosterone levels by 27% (to 436 ng/dL) and free testosterone levels by 34% (to 11.8 ng/dL). A pharmacodynamic study of testosterone suppression by polyestradiol phosphate in men with prostate cancer found that estradiol levels of about 135 pg/mL (500 pmol/L) would decrease testosterone levels by 50% (from 430 ng/dL to 215 ng/dL), while estradiol levels of about 410 to 545 pg/mL (1500–2000 pmol/L) would decrease testosterone levels well into the castrate range to about 6 to 12 ng/dL (0.2–0.4 nmol/L).