The Women's Health Initiative hormone trials

Don't read the WHI as "hormone therapy is dangerous for everyone", and don't read its reappraisal as "hormone therapy prevents disease". Its own investigators' conclusion holds: use hormone therapy to treat menopause symptoms, where the balance is better under 60, not to prevent heart disease, dementia or other chronic disease at any age.

What the trials tested, and in whom

The WHI hormone programme had two placebo-controlled arms. Women with a uterus took oral conjugated equine estrogens plus the synthetic progestin medroxyprogesterone acetate; women without a uterus took the estrogen alone.

The women had an average age of 63 and were typically more than ten years past menopause. The 2002 publications generalised what happened to them to every postmenopausal woman, and prescribing collapsed for two decades. Later analyses that split the results by age at starting recovered a more favourable picture for women who began early ^[1]. See Menopausal hormone therapy for why the trials designed to test that timing idea measured artery scans rather than heart attacks.

Breast cancer: the progestin, not the estrogen

The breast cancer signal that drove the 2002 alarm came from the combined arm, and medroxyprogesterone acetate is the progestin behind it. In the estrogen-alone arm, extended follow-up found lower invasive breast cancer incidence and lower breast cancer mortality than on placebo ^[2]. Large observational studies disagree and find a small excess even with estrogen alone; the details are in the main article.

Dementia: harm when started at 65 or later

The WHI Memory Study enrolled women aged 65 and older. Combined estrogen-progestin doubled their risk of dementia: 40 cases against 21 on placebo, or 45 against 22 per 10,000 women a year ^[3]. Estrogen alone, in the same programme, did not significantly raise it: 28 cases against 19.

Fractures: a real benefit that didn't tip the balance

Over 5.6 years, 8.6% of women on estrogen-progestin had a fracture against 11.1% on placebo, about 2.5 fewer fractures per hundred women, and the effect was the same at every age. Across all the trial's outcomes, though, there was no net benefit, even in women at high fracture risk, so the trial does not support hormone therapy as a bone-only prescription ^[4]. The WHI and one other American trial supply roughly 70% of all the randomised fracture data on hormone therapy ^[5].

Deaths: no change overall after 18 years

Over 18 years of follow-up, deaths from any cause did not move in either arm. With estrogen alone the difference was about 6%, well inside what chance would produce. What moved were particular causes: deaths coded to Alzheimer's disease or other dementia were about a quarter lower on estrogen alone than on placebo (2.4% against 3.2%) ^[6]. Read that carefully: it is a cause-of-death label rather than a confirmed diagnosis, it sits inside a broad "other deaths" category, and the investigators themselves set it against the Memory Study's finding of more dementia on hormone therapy.

What the WHI now says, and what changed on the label

The WHI's 20-year review concludes that hormone therapy should not be used to prevent heart disease, stroke, dementia or other chronic disease at any age, while its balance of benefit and risk is more favourable in women under 60 treating symptoms ^[7]. For women starting more than ten years after menopause or over 60, the risk of heart attack, stroke and blood clots rises in the first year or two with no offsetting heart benefit ^[8].

In February 2026 the US Food and Drug Administration (FDA) approved label changes removing the heart-disease, breast-cancer and probable-dementia boxed warnings, keeping only the endometrial-cancer boxed warning on systemic estrogen-alone products ^[9]. That reinterprets the same trials; it is not new evidence.

What to do

1. If you are under 60 or within ten years of menopause and have symptoms, don't let the 2002 headlines rule out hormone therapy; discuss it with a clinician.
2. If you are over 60 or more than ten years past menopause and have never taken it, treat starting as a riskier decision that needs a clear reason.
3. Don't take hormone therapy to prevent heart disease or dementia.

Further reading

• Manson JE et al. The Women's Health Initiative Randomized Trials and Clinical Practice: A Review. JAMA 2024.^[10]
• Shumaker SA et al. Estrogen plus progestin and the incidence of dementia and mild cognitive impairment in postmenopausal women: the Women's Health Initiative Memory Study: a randomized controlled trial. JAMA 2003.^[11]
• Cauley JA et al. Effects of estrogen plus progestin on risk of fracture and bone mineral density: the Women's Health Initiative randomized trial. JAMA 2003.^[12]
• Manson JE et al. Menopausal Hormone Therapy and Long-term All-Cause and Cause-Specific Mortality: The Women's Health Initiative Randomized Trials. JAMA 2017.^[13]
• Mehta JM, Chester RC, Kling JM. The Timing Hypothesis: Hormone Therapy for Treating Symptomatic Women During Menopause and Its Relationship to Cardiovascular Disease. J Womens Health 2019.^[14]