estrone, a derivative of estradiol and the second most dominant estrogen; and
estriol, a very short-acting estrogen and
the least biologically active.
The first misconception is that US Food and Drug Administration (FDA)-regulated drugs are not bioidentical. This is wrong. A long list of FDA-approved hormone products contain 17-beta estradiol and, therefore, are bioidentical. Examples include oral esterase, estradiol transdermal patches (Climara®, Vivelle®) and the vaginal ring (Estring®).