Estradiol vs estriol — what's the difference?
Reviewed by Kindr Health Clinical Team · Last reviewed July 3, 2026
Answer published
Estradiol (E2) is the main estrogen the ovaries produce during the reproductive years and is the molecule in every FDA-approved systemic HRT product. Estriol (E3) is a weaker estrogen that the body produces in large amounts during pregnancy but only trace amounts otherwise. Compounded "Biest" (typically 80% estriol / 20% estradiol) creams are popular in cBHRT marketing but lack the same level of randomized evidence. Vaginal estriol cream is well studied for genitourinary syndrome and is the one context where estriol has solid evidence — though estradiol vaginal cream is more widely prescribed in the U.S.
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