Estradiol (oestradiol, E2)

What estradiol is

Estradiol, more precisely 17β-estradiol, is the most important of the body’s own estrogens. As a medicine it is prescription-only and is used mainly in menopausal hormone therapy, together with a progestogen such as progesterone if the uterus is intact. There are preparations to take by mouth and to apply to the skin.

In the biohacking scene, estradiol has two faces. In women it is regarded as a key to healthy aging of the heart, brain and bones. In men it is often seen only as a nuisance to be pushed down with aromatase inhibitors such as anastrozole during testosterone therapy. Both pictures can be measured against studies. It should not be confused with its weakly active mirror image 17α-estradiol.

How it works

After menopause, the body’s own estrogen production drops sharply. Medicines replace it and relieve the associated symptoms. They contain estradiol or estradiol valerate, which is split in the body into 17β-estradiol and is chemically and biologically identical to the endogenous hormone (product information).

In men, estradiol is formed from testosterone by the enzyme aromatase. Which effects in men are due to estrogen rather than testosterone was worked out in a study with targeted hormone control in 400 healthy men: estrogen deficiency mainly explained the increase in body fat, testosterone deficiency the loss of muscle and strength, and both contributed to the decline in sexual function (Finkelstein 2013). In adult men, estradiol is the main factor for bone (Finkelstein 2016).

What the studies show

ELITE 2016: the timing of the start

643 healthy women received oral estradiol (with vaginal progesterone if the uterus was intact) or placebo, divided by whether menopause was less than 6 or at least 10 years ago; median 5 years. With an early start, carotid wall thickness increased more slowly under estradiol, 0.0044 versus 0.0078 mm per year; with a late start there was no difference. Coronary calcium, stenosis and plaque on cardiac CT did not differ in either group.

KEEPS 2014: patch or tablet shortly after menopause

727 women aged 42 to 58, 6 to 36 months after their last period and with hardly any coronary calcium, received an estradiol patch, conjugated estrogens as a tablet (each with progesterone) or placebo for 4 years. Carotid wall thickness increased equally in all groups, and coronary calcium did not differ either. Insulin resistance fell with the patch, blood pressure did not change, and serious adverse events were not more frequent. The trial was too small for clinical events.

DOPS 2012: events over 10 years

1,006 healthy women, on average 7 months after menopause, received, open-label in Denmark, hormone therapy with estradiol (with norethisterone if the uterus was intact) or no treatment. After 10 years, the composite endpoint of death, hospital admission for heart failure and heart attack occurred in 16 versus 33 women (HR 0.48). Cancer and breast cancer were not more frequent, but event numbers were small, and treatment was stopped after about 11 years because of the results of other trials.

Finkelstein 2013 and 2016: what estradiol does in men

400 healthy men aged 20 to 50 received a drug that switches off their own hormone production, plus testosterone gel in different amounts or placebo; half also received anastrozole, which prevents conversion into estradiol. This made it possible to separate what testosterone and what estradiol does. Estrogen deficiency mainly explained the rise in body fat, both hormones the declining sexual function. In bone, breakdown rose considerably more when estradiol was also missing, and spinal bone density fell in all groups without estradiol, regardless of the amount of testosterone.

PATCH/STAMPEDE 2026: estradiol patches in prostate cancer

1,360 men with locally advanced prostate cancer, median age 72, received estradiol patches or the usual hormone-deprivation injection with LHRH agonists at 75 UK centers. In the first year, testosterone was in the castrate range in 85 percent of those continuing treatment in both groups. After 3 years, 87.1 versus 85.9 percent were alive without metastases; after 5 years, 81.1 versus 79.2 percent were alive overall. Hot flashes occurred in 44 instead of 89 percent with the patch, breast enlargement, by contrast, in 85 instead of 42 percent.

Where the data stop

• Heart protection through an early start. ELITE showed slower thickening of the carotid wall with an early start, KEEPS did not, and on cardiac CT ELITE found no difference. The only trial with fewer events, DOPS, was open-label and small. Estradiol is not approved for preventing cardiovascular disease.
• Brain and dementia. Protection against dementia has not been shown; according to the product information, there are signs of a higher risk when started after age 65.
• The thrombosis advantage of skin application. It comes from observational data, not from randomized trials with thrombosis as an endpoint.
• Estradiol targets in men. The thresholds from Finkelstein 2016 describe when bone starts to suffer. These studies do not provide a target range to which estradiol should be adjusted during testosterone therapy.
• Many risk figures do not come from estradiol. The large outcome trials of hormone therapy often used conjugated equine estrogens. The product information, too, bases its risk figures on the WHI data; how much estradiol differs has only been studied for individual risks such as thrombosis.

Status, approval and legal

Estradiol medicines are approved and prescription-only in Germany. They are approved for hormone replacement therapy for symptoms of estrogen deficiency after menopause. The product information requires the lowest effective dose for the shortest possible duration and, if the uterus is intact, a progestogen on at least 12 to 14 days per cycle. Whether and how to treat is a medical decision after weighing symptoms and individual risk.

Estradiol patches for prostate cancer in men were tested in the PATCH trial. In sport, estradiol is not on the WADA Prohibited List 2026. Prohibited at all times, by contrast, are aromatase inhibitors such as anastrozole, letrozole and exemestane, and anti-estrogens such as tamoxifen and clomiphene (S4.1 and S4.2).

Safety

The risks of hormone therapy are well measured and depend on duration, combination and route of use. Breast cancer: in the worldwide analysis with 108,647 breast cancer cases, every form of hormone therapy except vaginal estrogen was associated with more breast cancer. For estrogen alone, the relative risk was 1.17 in years 1 to 4 of current use and 1.33 in years 5 to 14; with a progestogen it was higher. In women with obesity, estrogen alone was hardly associated with more breast cancer. After stopping, part of the risk persisted for more than 10 years (Collaborative Group 2019).

Uterus: estrogen alone raises the risk of hyperplasia and cancer of the uterine lining 2- to 12-fold, depending on duration and dose, if the uterus is intact; a progestogen is therefore added. Thrombosis and stroke: the product information gives a 1.3- to 3-fold risk of venous thromboembolism, highest in the first year, and up to 1.5-fold for ischemic stroke. In men, estradiol patches led to breast enlargement in 85 percent in PATCH. Anyone who notices symptoms or warning signs should discuss this with a physician.

Sources

• Hodis HN et al., N Engl J Med 2016 – ELITE, oral estradiol early or late after menopause, 643 women
• Harman SM et al., Ann Intern Med 2014 – KEEPS, estradiol patch or conjugated estrogens shortly after menopause, 727 women
• Schierbeck LL et al., BMJ 2012 – DOPS, hormone therapy with estradiol shortly after menopause and cardiovascular events, 1,006 women
• Vinogradova Y et al., BMJ 2019 – hormone therapy and venous thromboembolism by preparation and route, 80,396 cases
• Collaborative Group on Hormonal Factors in Breast Cancer, Lancet 2019 – type and duration of hormone therapy and breast cancer risk
• Finkelstein JS et al., N Engl J Med 2013 – testosterone, estradiol, body composition, strength and sexual function in 400 healthy men
• Finkelstein JS et al., J Clin Invest 2016 – testosterone, estradiol, bone turnover and bone density in men
• Langley RE et al., N Engl J Med 2026 – PATCH/STAMPEDE, estradiol patches versus LHRH agonists in locally advanced prostate cancer, 1,360 men
• German product information (Fachinformation) Gynokadin tablets 2 mg (Besins, as of September 2025)
• WADA Prohibited List 2026, informative German translation by NADA – S4.1 aromatase inhibitors, S4.2 anti-estrogens