In the early 2000s, a major women’s health study — Women’s Health Initiative (WHI) — made headlines. As an ongoing study launched in the ‘90s, the WHI asked: could menopause hormone therapy (MHT), used to ease menopause symptoms, also protect against serious health problems in later life?

A smaller arm, the WHI Memory Study (WHIMS), focused on brain health in women without dementia.

When results were released in 2002, they were shocking. Women on MHT were more likely — not less — to develop heart disease, stroke, breast cancer and dementia. Doctors quickly advised against MHT, prescriptions plummeted, and for years, MHT nearly disappeared from the conversation.

But the story the findings told at the time was incomplete. The WHI findings weren’t wrong; they revealed real risks. But in the years since, researchers have re-examined the WHI data — not only the brain findings, but also the heart, stroke and cancer results — to better understand when, why and how MHT should be used. Today, experts agree that for many women who start MHT around menopause and don’t have medical reasons to avoid it, the benefits outweigh the risks, and MHT can be safely prescribed to manage menopause symptoms.

Still, several myths about MHT have persisted, including misperceptions about how it affects brain aging.

Let’s bust a few of the biggest myths about MHT and brain health.

Myth 1: MHT raises the risk of dementia for all women

According to WHIMS, women who started MHT at 65 years or older were more likely to develop dementia than those who did not. But most women start MHT much earlier, typically in their 40s or 50s around menopause.

And timing is important to MHT.

Researchers describe this as the critical window hypothesis: starting MHT around menopause may support brain health, while starting years later may increase risk of cognitive decline and dementia. WHIMS didn’t test this “window” — most participants were long past menopause and no longer had menopause symptoms. So the results don’t show the effects of MHT when used at the right age, for the right reasons (experiencing menopause symptoms).

Recent studies show a mixed picture: some women who start MHT near menopause may see brain benefits in later life, like better memory and fewer dementia-related changes. Others see little difference in cognition and dementia risk — but not worse outcomes.

However, starting MHT much later, such as in your 70s or even more than five years after menopause, may link to greater tau protein build-up, which is a marker of Alzheimer disease.

In short, MHT isn’t automatically bad for the brain, but its effects may depend on when it’s started and what kind is used.

Myth 2: All MHT affects the brain the same way

When people hear “MHT” (formerly known as hormone replacement therapy or HRT), they may picture one standard treatment. But MHT comes in many forms, and these differences may matter. In WHIMS, women took conjugated equine estrogen pills and medroxyprogesterone acetate if they had a uterus. This combination was once the standard treatment, but is now rarely used.

Today, 17-beta estradiol, (a type of estrogen), is more common and linked to brain benefits and lower risk of cognitive decline.

Those with a uterus also take progestogens to reduce uterine cancer risk. Progestogens may support brain health, but could also blunt estrogen’s protective effects, including its role in the growth, maintenance and function of brain cells that support memory and thinking. Clearly, both hormone type and combination matter.

Delivery methods of MHT — which are available as pills, patches, gels, creams, sprays or vaginal rings — also matters because each is processed differently.

Oral pills pass through the liver and can increase risk of blood clots and high blood pressure, which can affect brain health by slowing blood flow and increasing stroke risk.

Patches and gels, absorbed through the skin, can carry lower risks by avoiding the liver.

The bottom line is that not all MHTs are created equal. But even with the right form and timing, can MHT prevent dementia?

Myth 3: WHIMS showed that MHT can prevent dementia

Somewhere along the way, MHT was recast from a treatment for menopause symptoms into a supposed defence against dementia. This misconception traces back to WHIMS, which asked whether MHT could reduce dementia risk.

But risk reduction isn’t prevention. WHIMS did not test whether MHT prevents dementia, and because the study enrolled women long after menopause, the results don’t show what happens when MHT is used during the menopause transition. Even so, the findings were often taken to support broader claims about MHT and brain health, even though MHT was never designed to prevent dementia or serve as a stand-alone strategy for lowering dementia risk.

And not everyone needs or should take MHT. Some women breeze through menopause; others struggle. MHT isn’t one-size-fits-all.

But why do some women have symptoms and others don’t? New research suggests menopause symptoms themselves may offer clues about brain health, possibly reflecting the brain’s sensitivity to falling estrogen. Since estrogen supports memory, thinking and mood, more symptoms might signal greater vulnerability to brain aging.

And it’s not just the symptoms — it’s their impact on daily life. When night sweats interrupt sleep or mood changes strain relationships, stress and fatigue may further tax the brain.

In short, MHT isn’t a magic shield against dementia. But for those who struggle and can safely take MHT, managing menopause symptoms may support current well-being and future brain health.

The next chapter for MHT

WHIMS marked an important first chapter in the MHT story, but the science is still unfolding.

Researchers are now asking: when is the best time to start MHT? Which hormones matter most? Who benefits, and why?

Menopause is personal. For some, MHT brings relief and better quality of life. It’s not a guaranteed defence against dementia. But for the right person, at the right time, MHT may support healthy brain aging — an encouraging sign for the next generation entering midlife with more knowledge and support than ever before.

Want to be part of this evolving story? Consider joining Canadian studies like CAN-PROTECT or BAMBI, which explore how MHT and menopause experiences shape brain aging.

This article is republished from The Conversation, a nonprofit, independent news organization bringing you facts and trustworthy analysis to help you make sense of our complex world. It was written by: Zahinoor Ismail, University of Calgary; Jasper Crockford, University of Calgary, and Maryam Ghahremani, University of Calgary

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Zahinoor Ismail receives funding from the Canadian Institutes of Health Research and Gordie Howe CARES.

Jasper Crockford receives funding from the Canadian Institutes of Health Research, Alberta SPOR Support Unit, Canadian Federation of University Women, Vascular Training Platform, and Brain Health Care Canada.

Maryam Ghahremani does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.