Estetrol

Estetrol is a reasonable option to discuss if you want an oral estrogen and live where it is approved, but it is not a proven safer pill. If you have a uterus you still need a progestogen with it, and if you have cardiovascular risk factors, a transdermal estradiol patch or gel remains the better-established choice.

What it is

Estetrol, often written E4, is an estrogen the human body makes naturally, but only in pregnancy, and only in the liver of the fetus. Its developers present it as a distinct class: a native estrogen that acts selectively in different tissues.

The evidence so far supports something narrower. Estetrol acts as an estrogen in vaginal tissue, bone and the brain and nervous system, with comparatively limited effects on the liver, including on clotting factors, and early breast samples look reassuring rather than conclusive ^[1]. Its favourable effects on blood vessels have so far been seen only in laboratory and animal work.

The European Commission approved it for menopausal symptoms in March 2026, as Fylrevy at 14.2 mg and 18.9 mg. A woman with a uterus needs a progestogen prescribed separately alongside it, to protect the womb lining. It is not approved for menopause in the US ^[2].

The main trial: it works on hot flashes, with side effects

The phase 3 trial behind the approval randomly assigned 640 women aged 40–65 to estetrol 15 mg, estetrol 20 mg or placebo for 12 weeks. Both doses reduced how often and how severely moderate-to-severe hot flashes struck, at weeks 4 and 12, compared with placebo; 15 mg was the lower of the two effective doses ^[3].

It is not side-effect free. Side effects judged to be caused by the drug hit 51.6% of women on 15 mg and 57.3% on 20 mg, against 20.6% on placebo. Few stopped because of them: 6.6%, 7.5% and 2.3% respectively.

Metabolism and bone: early, developer-run data

One phase 2 trial in 180 women carries the metabolic and bone picture. On estetrol, triglycerides barely changed, HDL ("good") cholesterol rose, fasting glucose did not change, insulin resistance and HbA1c (a three-month blood-sugar average) fell at the middle and upper doses, and a blood marker of bone breakdown (CTX-1) fell ^[4][5]. Both papers were written by the developer, and these are blood markers, not fractures or heart attacks.

A separate claim that estetrol causes no clinically meaningful change in blood pressure, including in women with existing cardiovascular risk factors, was presented at a 2025 conference and has not yet been peer-reviewed.

What hasn't been tested

There are no cardiovascular outcome data in postmenopausal women, and long-term data on blood clots are still pending. If the tissue-selective action holds up, estetrol would be the most promising attempt in years at an oral estrogen as safe for clotting as a patch. That is a hope, not a finding.

What to do

1. Treat estetrol as one more oral estrogen, not as a safer alternative to a patch or gel; see Menopausal hormone therapy for why the route matters.
2. If you have a uterus, take the progestogen prescribed with it.
3. Expect side effects to be more common than on placebo, and tell your clinician if they persist.
4. If you have cardiovascular risk factors, discuss transdermal estradiol first; a past blood clot needs an individual risk assessment before any hormone therapy.

Further reading

• Simoncini T et al. Estetrol (E4) for the treatment of moderate to severe vasomotor symptoms in postmenopausal women - Efficacy and safety results from the phase 3 E4COMFORT I multicenter, placebo-controlled study. Maturitas 2026.^[6]
• Douxfils J et al. Impact of estetrol (E4) on hemostasis, metabolism and bone turnover in postmenopausal women. Climacteric 2023.^[7]
• Gaspard U et al. A multicenter, randomized study to select the minimum effective dose of estetrol (E4) in postmenopausal women (E4Relief): part 1. Vasomotor symptoms and overall safety. Menopause 2020.^[8]
• Fylrevy (estetrol): EPAR. European Medicines Agency, 2026.^[9]