Does Oral Estradiol Cause Blood Clots? Reading the BMJ Study
Paper Cuts: Berggreen 2026. One paper, read past its summary.
Did you hear that oral estradiol is giving women blood clots? If you're on estradiol, that headline was written to land on you. It came from a Danish study in the BMJ in 2026, and its summary says oral estradiol was consistently linked to clots, regardless of dose and regardless of how long a woman took it.
I read the whole paper, appendix included. Its own figures disagree with both of those words.
Two words the data don't carry
Women taking estradiol with levonorgestrel, about 9 in 10 of them through a hormonal IUD, came out at 1.0, no increase, and the paper's own results list them as the exception. Women on the lower dose for more than five years showed no significant increase. Among women who started after 2002, more than five years showed no significant increase at either dose.
A summary that says more than its paper has a name: spin. A 2015 study found it in more than 8 out of 10 summaries of non-randomized studies of a treatment.
What kind of study this is
Denmark records every prescription a pharmacy fills. The researchers took women aged 50 to 69, about 10,000 who'd had a first clot and about 50,000 who hadn't, and looked back at their hormone prescriptions. Going by what she had bought, a woman counted as a current user if she was on a hormone at any point in the 90 days before the clot. So they know she paid for it. They don't know she took it, how often, or how much.
That's an observational study: a record of who filled what, set beside who got sick. It can raise a question. It can't answer one. For that you give a drug to some women, a placebo to others, and watch.
Who the "oral estradiol" women actually were
About 7 in 10 women in the oral estradiol group were taking it with a synthetic progestin, mostly norethisterone. Fewer than 1 in 4 took estradiol by itself. So the headline number, 1.6, is mostly a combination-pill number.
And not one result in this paper is about progesterone, the bioidentical hormone. It was sold in Denmark, and the authors say they didn't capture it.
"High dose" needs a translation too. Here it means anything above 1 mg a day, and Denmark's combination tablets come almost all in 1 mg or 2 mg. A woman handed the 2 mg tablet counted as high dose on her first day.
The clot signal follows the synthetic progestin
The paper's main results climb like a staircase. With levonorgestrel, the progestin that mostly stays in the uterus: 1.0. Estradiol alone: 1.4. Add norethisterone: 1.6. Add medroxyprogesterone: 1.9.
That 1.4 is what an observational study is built to produce: a hypothesis. The test of a hypothesis is a randomized trial, and five randomized trials gave women oral estradiol without a daily synthetic progestin. Not one of them showed an increase in clotting. One gave women aged 50 to 69, this study's exact age range, a 2 mg estradiol valerate tablet every day for two years, after a heart attack. That's this paper's high dose.
The only randomized trial of oral estradiol that did show more clots put estradiol and norethisterone in the same tablet, the same kind of pill most of the Danish women took, and gave it to women who had already had a clot.
In a 2023 American insurance database of women 50 to 64, a synthetic progestin taken by itself came in at about double the clot rate, while progesterone by itself showed no significant rise. Wherever there is a clot signal, it follows the synthetic progestin.
What they never measured
Their own diagram marks three variables with no direct data: smoking, weight and menopause. The registries never recorded whether a woman smoked, what she weighed, or when her periods stopped. Recent surgery, injury, a cast and being laid up in bed, some of the biggest clot triggers there are, don't appear in their adjustments.
To cover smoking and weight, they leaned on income and education, plus a lung-disease diagnosis for smoking, which by their own description only partly covers either. For education tracking both, they cited one 2001 paper. That paper has no weight data in it. And among Danish women born between 1931 and 1960, more than half of even the most educated had smoked. The smoking status isn't in this study, and nothing in it can stand in for that. Obesity alone carries nearly 2.5 times the risk of a first clot in other research.
Their own admission
With no age at menopause, the authors wrote that their stroke and heart attack results in women who started before 50, and in long-term high-dose users, "may partly reflect confounding by indication." In plain words: part of what they measured may be the reason she was prescribed the hormone, not the hormone.
For clots, the risk ran the other way over time. Their biggest clot number in the main results, 3.2, is in the first year at the higher dose, and by their own count high-dose users past five years had a reduced clot risk compared with high-dose users in their first year.
They called a pooled trial figure "comparable" to theirs, then wrote that most of those trials used horse estrogen, not estradiol.
The sloppiness tally
A claim its own figures don't support, written three times: summary, key findings box, discussion.
A citation for body weight that contains no weight data.
An appendix result printed as 1.9 with a range of 0.7 to 1.4. A number can't sit outside its own range.
Progesterone, the one hormone the paper reports nothing about, misspelled in its own product table.
Even on their own numbers
Among 10,000 women not on hormones, about 16 had a first clot in a year. Among 10,000 on oral therapy, they estimate 9 more. That's roughly 1 extra clot per 1,000 women a year, counted without knowing who smoked or what she weighed, with no adjustment for recent surgery, and with most of those women on a synthetic progestin.
The other side of the scale is empty. The paper never weighs a single benefit: not the hot flashes, not the bone, not the sleep.
Read past the headline
Women in their 60s and 70s are going to stay afraid of hormones because of this paper, and they deserve better than a headline the paper itself can't carry.
In my practice, I give as much estradiol as my patients need. The only thing that really changes the dosing is when she starts. The later she starts, the slower we go.
Find a provider who reads the whole paper, not just the headline. To read one yourself, start with Oral Estradiol and Blood Clot Risk: How to Read the Study.
The whole argument:
Listen to the podcast special on Spotify
⚠️ Educational content, not individual medical advice, diagnosis or a treatment recommendation. Nothing here tells any woman what to take, and nobody should start, stop or change a prescription because of an article. Your own labs and history belong in a one on one.
🩺 DNP led telehealth hormone optimization. Book a consultation and find everything: withinyou.health/links
Sources
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Berggreen, J., Pourhadi, N., Wood-Kurland, H., Løkkegaard, E., Torp-Pedersen, C., & Meaidi, A. (2026b). Contemporary menopausal hormone therapy and thrombotic disease: Nationwide nested case-control study [Supplementary appendix]. BMJ, 394, e100688.
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