The three major naturally occurring estrogens in women are estrone (E1), estradiol (E2), and estriol (E3). Estradiol (E2) is the predominate form in nonpregnant females, estrone is produced during menopause, and estriol is the primary estrogen of pregnancy. In the body these are all produced from androgens through actions of enzymes.
- From menarche to menopause the primary estrogen is 17β-estradiol. In postmenopausal women more estrone is present than estradiol.
- Estradiol is produced from testosterone by aromatase and estrone from androstenedione.
- Estrone is weaker than estradiol.
Premarin, a commonly prescribed estrogenic drug, contains the steroidal estrogens equilin and equilenin, in addition to estrone sulfate but due to its health risk, more genetic estrogen named Progynova (estradiol valerate) are now more often prescribed.
A range of synthetic and natural substances have been identified that also possess estrogenic activity.
- Synthetic substances of this kind are known as xenoestrogens.
- Plant products with estrogenic activity are called phytoestrogens.
- Those produced by fungi are known as mycoestrogens.
Unlike estrogens produced by mammals, these substances are not necessarily steroids.