The Study That Scared a Generation. What WHI Got Wrong, and What We Know Now.

In July 2002, the front page of every major newspaper carried the same story.

A landmark American study had been stopped early because hormone replacement therapy was causing breast cancer, heart attacks and strokes.

What followed was unprecedented. In Australia, MHT prescribing fell by 55% between 2001 and 2005 [1]. By 2008, the drop reached 67% [2]. A generation of women lost access to a treatment that, for many of them, could have transformed how they experienced menopause.

GPs who had prescribed it confidently became reluctant to mention it. Women who had been on it for years stopped overnight.

The study was called the Women's Health Initiative. WHI for short.

Nearly twenty-four years later, the data from WHI itself, plus the studies that have followed, tell a very different story than the one on those 2002 front pages. The treatment was not as dangerous as the headlines made it sound. The women in the study were not who most women starting MHT actually are. And the way the results were communicated cost women, and GPs, more than two decades of unnecessary fear.

The WHI was a legitimate, large, well-funded trial. It produced useful data. The problem was not with the science. It was with how the data were communicated, by statisticians and by journalists, and how that communication shaped public understanding for the next twenty years.

Personally, I was not afraid of MHT. But I had not heard the fear either.

Menopause was not part of the curriculum in my nursing training, or my Health Science degree. My mother did not discuss menopause with me. I have no idea whether she ever used MHT. It was simply not a conversation that happened in my family or my early professional life.

It was not until I started talking with other women about menopause myself, particularly when I was thinking of starting MHT, that I began to hear the fear. Most of it traced back to those 2002 headlines, even when the women telling me could not name the study. For most, it distilled to a vague but persistent sense that "MHT is just full of risk."

That sense did not come from nowhere. It came from 2002. And now it is time for that to change.

What was the WHI actually trying to find out?

The Women's Health Initiative was launched in the United States in 1991. It was the largest study of women's health ever undertaken, with more than 160,000 women enrolled across multiple trials.

The MHT arm of WHI had two co-primary aims. The first was to test whether hormone therapy could prevent coronary heart disease in older postmenopausal women. The second was to track its effect on invasive breast cancer risk over time [3].

This is the first thing to understand. WHI was not designed to test whether MHT helped women going through the menopause transition (the years leading up to and immediately after a woman's final period, when symptoms are most active for many women). It was designed to test whether MHT could prevent disease in older women who were many years past their final period.

The average age of women in the WHI MHT trial was 63.2 years [4]. Many were more than ten years past their final period, technically postmenopausal long before they enrolled.

A significant proportion already had health issues before they ever started MHT. They had high blood pressure. They were overweight or obese. They had other cardiovascular risk factors. These were not problems caused by MHT. They were problems the women already had at the point of enrolment.

Most of these women were not the women whose hot flushes and broken sleep brought them to a GP appointment. They were being asked whether MHT could prevent disease in older age, not whether it could ease the symptoms of the menopause transition.

It is a different population, and the question being asked of them was a different question too.

As Jean Hailes summarised it in 2024: "What seemed to be lost to many in the global audience was the fact that the aim of the WHI trial was to test whether taking oestrogen, either alone or with progesterone, after menopause could help prevent heart disease, stroke and cognitive decline in women" [5].

What hormones did WHI actually use?

The hormones used in WHI were not the body-identical hormones now considered first-line in Australia.

The oestrogen was conjugated equine oestrogen, a mixture of oestrogens derived from pregnant mare urine, sold as Premarin. The progestogen used in women with a uterus was medroxyprogesterone acetate, sold as Provera, a synthetic progestin that has a different structure, and a different risk profile, to the body's own progesterone [3].

This matters because the modern Australian preference is for body-identical oestradiol, usually delivered through the skin via a patch, gel or spray, combined where needed with micronised progesterone, which is chemically identical to the progesterone the body produces. These are not the same molecules WHI tested. The Australasian Menopause Society and Jean Hailes both note this distinction in their current position statements [6,7].

What did the headlines say, and why did they land so hard?

When WHI published its first major results in 2002, the combined oestrogen-plus-progestin arm of the trial was stopped early. The reason given was an increased risk of breast cancer, heart attack, stroke and blood clots [3].

The headlines focused on relative risk, the percentage increase compared to women not taking the treatment. That is what generated the panic. A "twenty-six percent increase in breast cancer risk" sounds enormous.

What the headlines did not focus on was absolute risk, the actual number of additional cases per thousand women per year. In WHI's combined arm, the increase translated to fewer than one additional case of breast cancer per thousand women per year [3].

That is roughly the same additional risk as drinking two glasses of wine a day, or being moderately overweight.

This is the comparison most women have never been told. Each of these carries a similar additional breast cancer risk to the one that frightened them off MHT.

Alcohol is independently linked to breast cancer in women, regardless of menopausal status, and regardless of whether MHT is being used. A 2019 case-control study published in Nutrients found that regular alcohol consumption was associated with a substantially increased risk of breast cancer in both pre and postmenopausal women [8]. Cancer Council Australia and the Australian Department of Health both classify alcohol as a known cause of breast cancer in women, alongside the World Health Organization's International Agency for Research on Cancer [9,10,11].

Neither the relative risk number nor the absolute risk number from WHI was wrong. They were the same data, expressed differently. But relative risk made for better headlines, and the comparison with everyday lifestyle risks that women rarely worry about was almost never made.

The next blog in this series goes into the breast cancer evidence in more detail, including the genuine differences between oestrogen-only MHT and combined MHT.

What did WHI actually show when looked at by age?

In the years since 2002, researchers have re-analysed the WHI data by age group. What they found is now central to how MHT is understood worldwide.

For women who started MHT within ten years of menopause, or before age sixty, the picture looked very different. As Jean Hailes summarised in 2024: "An analysis of the WHI data published in 2017 found that women in the study who used hormone therapy for between five and seven years did not have an increased risk of all-cause, cardiovascular or cancer mortality during the 18-year follow up. And for women in their 50s, there was actually a trend towards a reduced risk of mortality" [5,12].

In this group, the women who actually present clinically asking about MHT for symptoms, the data showed:

- A reduction in all-cause mortality on long-term follow-up [12]

- A neutral or favourable effect on cardiovascular outcomes

- A substantial reduction in fractures from osteoporosis

- An increase in breast cancer in the combined arm that was small in absolute terms, and a reduction in breast cancer incidence and mortality in the oestrogen-only arm

This led to what is now called the timing hypothesis, or the window of opportunity. The principle is straightforward. Starting MHT close to menopause, when the cardiovascular system is still healthy, gives a very different risk-benefit profile to starting it a decade or more later, when atherosclerosis (narrowing and hardening of the arteries) may already be established.

The window of opportunity is now central to how the Australasian Menopause Society, the International Menopause Society, the North American Menopause Society, and the UK National Institute for Health and Care Excellence frame MHT prescribing [6,13,14].

What does the breast cancer evidence actually say?

Of all the WHI findings, the breast cancer signal caused the most fear, and the most enduring damage to MHT prescribing.

What is now well-documented from WHI's own long-term follow-up data is something most women, and many GPs, never heard.

Dr Avrum Bluming, a medical oncologist whose practice was 60% devoted to breast cancer, summarised it directly in CA: A Cancer Journal for Clinicians in 2024: "According to WHI's own data, estrogen alone significantly decreases the risk of breast cancer development (by 23%) and the risk of breast cancer death (by 40%), crucial information for women who have had hysterectomies" [15].

This applies to women on oestrogen-only MHT, which is what is prescribed for women without a uterus. It is one of the most under-publicised findings in the entire MHT literature.

For women with a uterus, who need both oestrogen and a progestogen, the picture is more nuanced, and the type of progestogen matters. The detail of this, including the difference between body-identical micronised progesterone and older synthetic progestins, is covered in the next blog in this series.

What this means in plain terms: the breast cancer fear that drove a generation of women off MHT does not match what the current evidence, including WHI's own long-term data, actually shows.

What does the science say now?

The international position has shifted substantially.

The Australasian Menopause Society, the North American Menopause Society, and the UK National Institute for Health and Care Excellence all now support MHT as appropriate for women under sixty, or within ten years of menopause, who are experiencing menopausal symptoms or have specific clinical indications [6,13,14].

This does not mean every woman should be on MHT.

What it does mean is significant. And it deserves greater attention than it has received. The WHI panic that ended a generation of MHT prescriptions was based on a misreading of who the study was actually testing. The women in the study were older, often had health issues already, and were taking hormones that are no longer the modern Australian first-line. Today, most Australian women starting MHT are prescribed body-identical oestradiol through the skin and, where needed, body-identical micronised progesterone. These are different molecules to those used in WHI. The treatment was not as dangerous as the headlines made it sound. And the modern position, supported by more than two decades of follow-up data, is far more nuanced than the 2002 headlines suggested.

When women work with me and tell me they have been refused MHT because of the WHI study, my first question is always: when was that conversation? If the answer is more than a few years ago, the evidence has moved on. The conversation is worth having again.

If you have been told MHT is too risky because of WHI, the advice you are being given is more than two decades out of date.

If your mother or your aunt told you MHT was unsafe, the evidence has changed since they were given that message.

This does not mean the answer is yes for everyone. MHT has risks, contraindications, and benefits. The decision is individual. It belongs to you, in conversation with a GP who keeps up with current menopause evidence and guidelines.

The point is this. If you decided against MHT because of what you read or heard in 2002, that decision was based on the information available then. The information has changed. Whether or not you choose MHT, the question is worth looking at again.

In simple terms

- WHI was a legitimate, large, well-funded study, and it produced useful information. The fault was not with the science. It was with how the results were communicated, by statisticians and by journalists, and how those reports shaped public understanding.

- The average woman in WHI was 63 years old, more than ten years past menopause, and not having symptoms. Many already had health issues before starting MHT. She is not the typical woman starting MHT today.

- WHI used older hormones (conjugated equine oestrogen and synthetic progestin), not the body-identical oestradiol and micronised progesterone that are first-line in Australia today.

- The additional breast cancer risk from combined MHT in absolute terms is comparable to drinking two glasses of wine a day, or being moderately overweight. Alcohol independently raises breast cancer risk regardless of MHT use.

- For women starting MHT within ten years of menopause, the long-term data show no increased mortality, and a trend towards reduced mortality for women in their 50s.

- WHI's own long-term data show oestrogen-only MHT decreases breast cancer development by 23% and breast cancer death by 40%.

- If you decided against MHT because of what you read or heard in 2002, the evidence has shifted. The question is worth revisiting.

Want the complete picture?

There are three free resources to take this further.

[PLACEHOLDER] Audio guide on WHI and MHT. A 10-minute audio overview in plain language. menopausehub.com.au/whi-audio (URL to be confirmed).

[PLACEHOLDER] WHI Key Fact Sheet. A one-page reference you can keep or take to your GP. menopausehub.com.au/links (when published).

[PLACEHOLDER] MHT Complete Guide. The full plain-language guide. menopausehub.com.au/links (when published).

Next in the series

The next blog goes deeper into the breast cancer question. What the evidence actually says, in absolute numbers, including the genuine differences between oestrogen-only MHT, combined MHT with synthetic progestogens, and combined MHT with body-identical micronised progesterone. If breast cancer is the question that has stopped you from saying yes to MHT, the next blog is for you.

MHT and Breast Cancer. What the Current Evidence Actually Says.

This information is educational only and does not constitute personal medical advice. Always consult a qualified health professional about your individual circumstances.

© 2026 Menopause Hub | Anna Pattison | Former Registered Nurse, Clinical Myotherapist, Menopause Mentor | menopausehub.com.au

CITATIONS

[1] Velentzis, L.S., et al. (2016). Use of menopausal hormone therapy and bioidentical hormone therapy in Australian women 50 to 69 years of age. PLoS One, 11(3): e0146494.

[2] McGee, R.G., et al. (2020). Trends in prescribing menopausal hormone therapy and bisphosphonates in Australia and Manitoba, Canada. Journal of Women's Health, 29(2), 177-185.

[3] 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.

[4] 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.

[5] Jean Hailes for Women's Health. (2024). MHT still maligned and misunderstood: expert. jeanhailes.org.au

[6] Australasian Menopause Society. Position Statement on Menopausal Hormone Therapy. menopause.org.au

[7] Jean Hailes for Women's Health. Menopausal Hormone Therapy (MHT). jeanhailes.org.au

[8] Godinho-Mota, J.C.M., et al. (2019). Sedentary Behavior and Alcohol Consumption Increase Breast Cancer Risk Regardless of Menopausal Status: A Case-Control Study. Nutrients, 11(8), 1871.

[9] Cancer Council Australia. Alcohol and cancer risk. cancer.org.au

[10] Australian Department of Health and Aged Care. Alcohol and your health. health.gov.au

[11] International Agency for Research on Cancer (IARC), World Health Organization. Alcohol consumption and ethyl carbamate. IARC Monographs Volume 96. iarc.who.int

[12] Manson, J.E., et al. (2017). Menopausal hormone therapy and long-term all-cause and cause-specific mortality: the Women's Health Initiative randomized trials. JAMA, 318(10), 927-938.

[13] National Institute for Health and Care Excellence (NICE). (2024). Menopause: Identification and Management. NICE Guideline NG23.

[14] The North American Menopause Society. (2022). The 2022 hormone therapy position statement of The North American Menopause Society. Menopause, 29(7), 767-794.

[15] Fillon, M. (2024). The association between menopausal hormone therapy and breast cancer remains unsettled. CA: A Cancer Journal for Clinicians, 74(3), 217-222. Quote attributed to Dr Avrum Z. Bluming, MD.

[16] Anderson, G.L., et al. (2012). Conjugated equine oestrogen and breast cancer incidence and mortality in postmenopausal women with hysterectomy: extended follow-up of the WHI randomised placebo-controlled trial. Lancet Oncology, 13(5), 476-486.

[17] Davis, S.R., Magraith, K. (2023). Practitioner's Toolkit for the Management of the Menopause. Medical Journal of Australia.