Estrone (E1), also spelled oestrone, is a steroid, a weak estrogen, and a minor female sex hormone.

[1] Estrone, as well as the other estrogens, are synthesized from cholesterol and secreted mainly from the gonads, though they can also be formed from adrenal androgens in adipose tissue.

[1][10][11][12] This contradicts some cell-free in-vitro research suggesting that high concentrations of estrone might be able to partially antagonize the actions of estradiol.

[2] In addition to aromatization of androstenedione, estrone is also formed reversibly from estradiol by the enzyme 17β-hydroxysteroid dehydrogenase (17β-HSD) in various tissues, including the liver, uterus, and mammary gland.

[1] Mechanism of Action: The way estrone works is by entering the cells of certain tissues in the body and attaching to nuclear receptors.

[23] It is one of the three primary types of estrogen and is produced in various parts of the body, including the placenta, ovaries, and peripheral tissues.

[26] Estrone has been available as an injected estrogen for medical use, for instance in hormone therapy for menopausal symptoms, but it is now mostly no longer marketed.

[28] Estrone, as part of hormone replacement therapy (HRT), is frequently used to treat symptoms caused by estrogen deficiency in peri and post-menopausal women.

This therapy aims to enhance overall health and relieve menopausal symptoms related to estrogen imbalance.

Additionally, estrone and other estrogens are used to prevent osteoporosis in postmenopausal women who are at high risk of fractures and cannot tolerate alternative medications.

Estrogens are absorbed efficiently by the body and subsequently inactivated in the liver, making them effective in HRT and osteoporosis prevention.

[25] The use of estrone has several contraindications, some examples including: hypersensitivity, history of some cancers, stroke, venous thromboembolism (VTE), and those currently pregnant or breastfeeding.

Estrogens hold a boxed warning to be used at the lowest effective dose and for the shortest possible treatment period if used alone or with another hormone in the progestogen class.

Estrone, the major type of estrogen produced in post-menopausal women, was seen in greater concentrations from standard levels in those that were categorized as prefrail and in those that classified as frail.

[34] Risk of developing initial VTE is also increased with familial history, genetic mutations: factor V Leiden and prothrombin-G20210A, and pregnancy-postpartum with the use of estrogens.

[36] Some adverse effects seen with the usage of estrogens include: increased risk of venous thromboembolism (VTE), stroke, breast cancer, hypertension, and vaginitis.