Estradiol vs estrone vs estriol: the three estrogens explained

The human body produces three estrogens in meaningfully different amounts depending on life stage. Knowing which is which, and which dominates when, makes lab results and prescription choices more legible.

Estradiol (E2) — the reproductive years dominant

Estradiol is the most potent of the three estrogens and the dominant one during reproductive years. Ovarian granulosa cells produce most of it, with smaller contributions from peripheral conversion. Estradiol levels track the menstrual cycle — peaking pre-ovulation, dropping during menses. In standard menopause panels, E2 is what most labs report. After menopause, estradiol levels fall to roughly one-tenth of premenopausal values.

Almost all FDA-approved estrogen therapy is estradiol — patches, gels, sprays, vaginal preparations, and most oral tablets. Doses range from 0.025 mg/day (low-dose patch) to 0.1 mg/day (standard transdermal), or 1–2 mg orally.

Estrone (E1) — the postmenopausal dominant

Estrone is the dominant estrogen after menopause. After ovarian function declines, the major source of estrogen becomes peripheral conversion of androstenedione (an adrenal androgen) to estrone, mostly happening in fat tissue. This is why postmenopausal women with more adipose tissue tend to have higher estrone levels — and why obesity is an independent risk factor for postmenopausal estrogen-sensitive cancers like endometrial cancer.

Conjugated equine estrogens (Premarin) contain a mix of estrone-based equine estrogens. Oral micronized estradiol also converts substantially to estrone in the liver, which is one reason transdermal preparations have different metabolic profiles than oral.

Estriol (E3) — the pregnancy estrogen

Estriol is the weakest of the three and the dominant estrogen during pregnancy, produced primarily by the placenta. Outside pregnancy, estriol levels are very low. Compounded bioidentical preparations marketed as "BiEst" (80% estriol / 20% estradiol) or "TriEst" (a three-estrogen mix) lean heavily on estriol despite limited evidence for postmenopausal use. ACOG and NAMS have specifically flagged the lack of efficacy and safety data for estriol-dominant formulations outside pregnancy.

Reading your lab

Standard menopause panels measure total estradiol (sometimes specified as "ultrasensitive estradiol" using LC-MS/MS at low ranges typical of postmenopause). Estrone is occasionally added in specific clinical contexts (suspected aromatase excess, monitoring tamoxifen). Estriol is rarely measured outside pregnancy and obstetric monitoring. Saliva and urine estrogen testing marketed by some compounding pharmacies is not validated for clinical decision-making.

Informational only — your clinician interprets estrogen labs in the context of your symptoms, cycle status, and treatment.