In 2002, the Women's Health Initiative trial published findings that linked hormone replacement therapy to increased rates of breast cancer and cardiovascular events. HRT prescribing in the UK dropped by over 60 percent in the years that followed. What took years to communicate was that the WHI used synthetic progestins combined with oral conjugated equine oestrogen in women who were, on average, 63 years old and more than a decade post-menopause. That is not how most women were taking HRT, and the findings did not translate cleanly to the population actually being treated.
What the Subsequent Evidence Shows
Reanalysis of the WHI data, along with multiple large observational studies and randomised trials in the two decades since, has produced a significantly more nuanced picture. For women under 60 or within 10 years of menopause onset, the evidence consistently shows that HRT reduces all-cause mortality, reduces cardiovascular disease risk, significantly reduces bone fracture risk, and substantially improves quality of life. The breast cancer signal from the WHI was largely associated with the synthetic progestin component, not with oestrogen alone.
The NICE Guidance
The National Institute for Health and Care Excellence updated its menopause guidelines most recently in 2023 and recommends that the benefits of HRT outweigh the risks for the majority of women with menopausal symptoms. It specifically recommends that women be offered HRT after individualised discussion, and notes that the risks associated with transdermal oestrogen and micronised progesterone are lower than those seen in the WHI with oral oestrogen and synthetic progestins.
What the Evidence Does Not Support
HRT is not without any risk. The increased risk of breast cancer associated with combined HRT is real, though modest, and approximately equivalent to the risk associated with two units of alcohol per day or being overweight. Women with certain personal or family histories should discuss this carefully with a clinician. HRT does not appear to benefit women who start it more than 10 years after menopause; the cardiovascular protection seen in earlier starters is not replicated in later starters. The decision is individual, not universal.
Sources
- Rossouw, J.E., et al. (2002). Risks and benefits of estrogen plus progestin in healthy postmenopausal women: principal results from the Women's Health Initiative randomized controlled trial. JAMA, 288(3), 321-333.
- Manson, J.E., et al. (2013). Menopausal hormone therapy and health outcomes during the intervention and extended poststopping phases of the Women's Health Initiative randomized trials. JAMA, 310(13), 1353-1368.
- NICE Guideline NG23. (2023). Menopause: diagnosis and management. National Institute for Health and Care Excellence.
- Baber, R.J., et al. (2016). IMS Recommendations on women's midlife health and menopause hormone therapy. Climacteric, 19(2), 109-150.