From the FDA Drug Label
Although circulating estrogens exist in a dynamic equilibrium of metabolic interconversions, estradiol is the principal intracellular human estrogen and is substantially more potent than its metabolites, estrone and estriol, at the receptor level Estradiol is converted reversibly to estrone, and both can be converted to estriol, which is the major urinary metabolite.
Estriol (E3) is a naturally occurring estrogen and a metabolite of estradiol and estrone. It is less potent than estradiol at the receptor level and is the major urinary metabolite of estradiol and estrone 1.
From the Research
Estriol is a naturally occurring estrogen hormone produced by the human body, primarily during pregnancy, and is considered the weakest of the three main estrogens in terms of estrogenic activity.
Key Characteristics of Estriol
- It is one of three main estrogens, alongside estradiol and estrone.
- Estriol is sometimes used medically as a component in hormone replacement therapy for menopausal symptoms, particularly for vaginal symptoms like dryness, irritation, and painful intercourse.
- The hormone works by binding to estrogen receptors in vaginal tissues, helping to restore thickness, elasticity, and lubrication.
- Estriol is available in various forms including vaginal creams, suppositories, and tablets, typically dosed at 0.5-1 mg daily for vaginal applications.
Clinical Use and Safety Profile
- Some clinicians prefer estriol for local vaginal treatment because it has less systemic absorption compared to other estrogens, potentially offering a better safety profile regarding breast and endometrial stimulation 2.
- While generally considered safer for localized use, estriol still carries some of the risks associated with estrogen therapy and should be used at the lowest effective dose for the shortest duration necessary to control symptoms.
- Emerging evidence indicates that estriol has potential immunomodulatory benefits for many disease states including autoimmune, inflammatory, and neurodegenerative conditions 2.
Comparison with Other Estrogens
- Estriol has a unique mode of action and metabolism compared to other estrogens, which may support its favorable benefit-risk ratio 3, 4.
- The use of oral estrogens for contraception or menopause is also associated with unwanted effects, such as an increased risk of breast cancer and thromboembolic events, due to their impact on non-target tissues 3.
- Estriol may offer a potentially cost-effective approach to a variety of conditions and may offer a wide range of health benefits, including improved control of menopausal symptoms and better urogenital health 2.