HRT for Women: What the Evidence Shows About Hormone Therapy After Menopause
Few topics in women's health have been debated as fiercely as menopausal hormone therapy. The 2002 Women's Health Initiative results changed practice almost overnight, and two decades of follow-up and re-analysis have since added important detail about who benefits, who is at risk and how preparations differ.
- The 2002 Women's Health Initiative (WHI) trial tested oral conjugated equine estrogen plus medroxyprogesterone acetate in 16,608 women aged 50 to 79. Overall, risks exceeded benefits: per 10,000 women each year there were 7 more heart disease events, 8 more strokes, 8 more pulmonary embolisms and 8 more invasive breast cancers, against 6 fewer colorectal cancers and 5 fewer hip fractures.1
- Timing matters, though less decisively than often claimed: in a WHI re-analysis, heart disease risk trended lower within 10 years of menopause (hazard ratio 0.76, not statistically significant) and higher 20 or more years after it (1.28), while stroke risk rose regardless of timing.2
- In a French case-control study, oral estrogen was linked to about four times the risk of blood clots (odds ratio 4.2), while transdermal estrogen was not (0.9). This is observational evidence, not a randomized trial.4
- Breast cancer risk depends on the preparation and on duration. In the French E3N cohort, estrogen with progesterone was not linked to higher risk, unlike estrogen with synthetic progestins, but a 2019 meta-analysis found that every type of systemic hormone therapy raised risk, more the longer it was used.5,6
- Over 18 years of follow-up, the WHI hormone therapy trials showed no effect on all-cause, cardiovascular or cancer mortality (hazard ratio 0.99 for all-cause mortality).7 Current guidance is to individualize treatment by age, time since menopause and preparation.9
After the trial's results were published in July 2002, US prescriptions fell month after month: in the first half of 2003, prescriptions for the estrogen-plus-progestin pill Prempro were 66% lower, and for the estrogen-only pill Premarin 33% lower, than a year earlier.8 Since then, longer follow-up and new analyses have clarified how the risks vary with age, timing and formulation.
What the WHI Actually Found - and What It Did Not
The WHI estrogen-plus-progestin trial was a prevention study, not a trial of symptom relief. It randomized 16,608 postmenopausal women aged 50 to 79 with a uterus, at 40 US centres, to conjugated equine estrogen with medroxyprogesterone acetate, a synthetic progestin, or to placebo;1 the average participant was 63.3 After a mean of 5.2 years, the trial was stopped early because invasive breast cancer crossed its preset safety boundary. Heart disease (hazard ratio 1.29), stroke, pulmonary embolism and breast cancer were more common, colorectal cancer and hip fractures less common, and all-cause mortality did not change.1 These results apply to that preparation in that population, which is why later analyses examined age and timing.
The label has changed. The WHI results led the FDA to add a boxed warning, its most prominent safety warning, covering cardiovascular disease, breast cancer and probable dementia. On November 10, 2025, the FDA asked manufacturers to remove that language from the boxed warning, to drop the advice to use the lowest dose for the shortest time, and to remove the probable dementia warning, noting that the WHI participants averaged 63 and that the dementia studies enrolled women aged 65 to 79, older than most women starting treatment (FDA, November 2025). Information on cardiovascular disease and breast cancer stays in the labeling outside the boxed warning, and the boxed warning on endometrial cancer stays for systemic estrogen-alone products, which is why women with a uterus take a progestogen with estrogen. The first six updated labels were approved on February 12, 2026 (FDA, February 2026). The change alters how risk is presented; it does not make the WHI findings disappear, so age, time since menopause and personal risk still decide whether therapy makes sense.
The Timing Hypothesis: The Most Important Concept in HRT
Researchers have asked whether the effects of hormone therapy depend on age or on time since menopause, the idea behind the so-called timing hypothesis.2 The re-analyses below show how far the evidence supports it.
In a WHI re-analysis of 27,347 women from both hormone trials, the hazard ratio for heart disease was 0.76 within 10 years of menopause, 1.10 at 10 to 19 years and 1.28 at 20 or more years, a statistically significant trend, although the lower risk in the first group was not itself significant; by age group, the trend was not significant.2 Total mortality showed a non-significant tendency to be more favourable in younger women (hazard ratio 0.70 at ages 50 to 59), and stroke risk was raised regardless of time since menopause.2 Over 18 years of follow-up, hormone therapy did not change all-cause mortality overall, although during the treatment years its effect on mortality was more favourable in women aged 50 to 59 than in those aged 70 to 79.7 In younger women who had had their ovaries removed, estrogen alone was associated with 32% lower all-cause mortality over long-term follow-up.3
Formulation Matters: Transdermal Estradiol and Micronized Progesterone
Route matters for blood clots. In a French case-control study, current users of oral estrogen had about four times the risk of venous thromboembolism of non-users (odds ratio 4.2), while transdermal estrogen users did not have a higher risk (0.9), and micronized progesterone was not linked to clots.4 For breast cancer, the French E3N cohort of 80,377 women found a 1.29-fold risk with estrogen alone and a 1.69-fold risk with estrogen plus synthetic progestins, while estrogen with progesterone was not associated with higher risk (relative risk 1.00).5 A 2019 meta-analysis of individual participant data found excess breast cancer risk with every type of hormone therapy except vaginal estrogen, rising with duration and higher for estrogen-progestagen than estrogen-only preparations. If the link is causal, 5 years of use from age 50 would cause about one extra breast cancer for every 50 users of estrogen with daily progestagen, 70 with intermittent progestagen and 200 with estrogen alone.6
Who Should and Should Not Consider HRT
| Situation | What the 2022 Menopause Society statement says |
|---|---|
| Under 60, or within 10 years of menopause, with no contraindications | The benefit-risk ratio is favourable for treating bothersome hot flashes and preventing bone loss |
| Starting more than 10 years after menopause, or over 60 | The benefit-risk ratio appears less favourable, because of greater absolute risks of heart disease, stroke, blood clots and dementia |
| Longer use | Should be for documented reasons, such as persistent hot flashes, with shared decision-making and regular reassessment |
The statement adds that hormone therapy remains the most effective treatment for hot flashes and the genitourinary syndrome of menopause and prevents bone loss and fracture, and that its risks differ by type, dose, duration, route, timing of initiation and whether a progestogen is used, so treatment should be individualized.9
Put this research into practice: What Should I Test Next?
References
- 1Rossouw JE, et al. "Risks and benefits of estrogen plus progestin in healthy postmenopausal women: principal results From the Women's Health Initiative randomized controlled trial." JAMA. 2002;288(3):321-33. PubMed · DOI
- 2Rossouw JE, et al. "Postmenopausal hormone therapy and risk of cardiovascular disease by age and years since menopause." JAMA. 2007;297(13):1465-77. PubMed · DOI
- 3Manson JE, et al. "The Women's Health Initiative trials of menopausal hormone therapy: lessons learned." Menopause. 2020;27(8):918-928. PubMed · DOI
- 4Canonico M, et al. "Hormone therapy and venous thromboembolism among postmenopausal women: impact of the route of estrogen administration and progestogens: the ESTHER study." Circulation. 2007;115(7):840-5. PubMed · DOI
- 5Fournier A, et al. "Unequal risks for breast cancer associated with different hormone replacement therapies: results from the E3N cohort study." Breast Cancer Res Treat. 2008;107(1):103-11. PubMed · DOI
- 6Collaborative Group on Hormonal Factors in Breast Cancer. "Type and timing of menopausal hormone therapy and breast cancer risk: individual participant meta-analysis of the worldwide epidemiological evidence." Lancet. 2019;394(10204):1159-1168. PubMed · DOI
- 7Manson JE, et al. "Menopausal Hormone Therapy and Long-term All-Cause and Cause-Specific Mortality: The Women's Health Initiative Randomized Trials." JAMA. 2017;318(10):927-938. PubMed · DOI
- 8Hersh AL, et al. "National use of postmenopausal hormone therapy: annual trends and response to recent evidence." JAMA. 2004;291(1):47-53. PubMed · DOI
- 9“The 2022 Hormone Therapy Position Statement of The North American Menopause Society” Advisory Panel. "The 2022 hormone therapy position statement of The North American Menopause Society." Menopause. 2022;29(7):767-794. PubMed · DOI
