Recent media coverage has once again raised questions about whether hormone replacement therapy (HRT) could affect a woman’s future risk of dementia. It is an important question, but the scientific evidence is more nuanced than a simple headline can convey.
For women considering HRT, concerns about cognitive health are entirely understandable. Dementia is more common in women than men, and there is growing interest in understanding whether the hormonal changes associated with menopause could play a role in long-term brain health.
So what does the evidence actually tell us?
The short answer is that there is currently no good evidence that menopausal hormone therapy as a class either increases or decreases the overall risk of dementia. However, the research is evolving, and factors including age, timing of treatment, formulation and individual risk may be important.
Where did concerns about dementia and HRT come from?
Much of the concern originates from the Women’s Health Initiative Memory Study (WHIMS), an important randomised controlled trial investigating cognitive outcomes in older postmenopausal women.
WHIMS enrolled women aged 65 and over, substantially older than the typical age at which women begin HRT to manage menopausal symptoms. Participants received either conjugated equine oestrogen, or conjugated equine oestrogen combined with medroxyprogesterone acetate, compared with placebo.
The combined hormone arm was associated with an increased incidence of probable dementia and mild cognitive impairment compared with placebo. These findings were important and understandably led to concern about the potential relationship between hormone therapy and cognitive health.
However, the context of the study is equally important.
The women participating in WHIMS were, on average, around 15 years beyond menopause. They were therefore very different from women who begin HRT during the perimenopause or in the years immediately following menopause.
The study also examined specific hormone formulations. It is therefore important not to assume that findings from this particular population, treatment regimen and age group automatically apply to every woman using contemporary menopausal hormone therapy.
This does not mean that the WHIMS findings should be dismissed. Rather, they need to be interpreted alongside the wider body of evidence.
Does the timing of HRT matter?
One of the most interesting areas of current research is whether the effect of hormone therapy on the brain may depend on when treatment begins. This is sometimes referred to as the “critical window” or “window of opportunity” hypothesis.
The theory is that there may be a difference between replacing hormones around the time of menopause, when oestrogen levels are changing, and starting hormone therapy many years later.
Evidence for this remains incomplete, but recent research has added to the discussion.
A large UK Biobank study published in 2026 followed more than 183,000 postmenopausal women for an average of around 13 years. Women who had used HRT for at least a year had lower rates of dementia and Alzheimer’s disease than women who had not used HRT. The association was strongest among women who started HRT between approximately 46 and 56 years of age, with particularly strong associations among some women who had experienced surgical menopause or had lower lifetime exposure to oestrogen.
These findings are interesting, particularly because they point towards the possibility that timing may matter.
But there is an important caveat: this was an observational study. It can identify an association between HRT use and dementia outcomes, but it cannot prove that HRT itself caused the reduction in risk. Women who use HRT may differ from those who do not in other ways that influence dementia risk, such as socioeconomic factors, healthcare access, education or underlying health.
The researchers themselves emphasise the need for further research to establish whether HRT is causally responsible for the differences observed.
What do the studies of cognitive function tell us?
Other research has looked more directly at cognition rather than waiting for dementia to develop.
The KEEPS study examined women who were relatively close to the menopause transition and compared different forms of hormone therapy with placebo. It did not find a clear cognitive benefit or evidence of cognitive harm.
The ELITE study similarly investigated whether the timing of oestrogen therapy in relation to menopause affected cognitive outcomes. It found no evidence of either cognitive benefit or harm in the groups studied.
These studies are reassuring in that they did not identify a clear cognitive-harm signal, but they also have important limitations. Neither was sufficiently large or long enough to determine whether hormone therapy changes the incidence of dementia itself.
In other words, not finding evidence of harm is not the same as proving that HRT prevents dementia.
What does the latest overall evidence show?
Perhaps the most useful way to put the current evidence into perspective is to look at the research collectively rather than focusing on any single study.
A systematic review and meta-analysis published in The Lancet Healthy Longevity in December 2025 examined ten studies involving more than one million women. Only one was a randomised controlled trial, with the remainder being observational studies.
The review found no significant association between menopausal hormone therapy and the risk of mild cognitive impairment or dementia. It also found no significant effects when the researchers looked at factors including timing, duration or type of hormone therapy.
The authors concluded that the available evidence does not currently show that menopausal hormone therapy either increases or decreases dementia risk. They also highlighted the need for better long-term studies looking specifically at formulation, dose, route of administration, timing and duration of treatment. This is an important finding because it helps put individual studies into context.
The evidence is not telling us that HRT is a treatment for dementia. But neither does it support the idea that HRT, in general, inevitably increases dementia risk.
What about “bioidentical” hormones?
It is also important to recognise that HRT is not a single treatment.
There are different types of oestrogen and progestogen, different doses and routes of administration, and different combinations of treatment. Research into one formulation cannot automatically be extrapolated to all forms of hormone therapy.
Studies including KEEPS and ELITE have investigated estradiol-based therapy in women closer to the menopause transition. They have not demonstrated a clear cognitive benefit or harm.
However, it would be too strong to interpret these studies as proving that bioidentical hormones protect against dementia. The studies were not designed or powered to provide a definitive answer about long-term dementia incidence.
For this reason, the most evidence-based position is one of careful interpretation rather than certainty.
So, does HRT prevent dementia?
At present, HRT should not be prescribed specifically as a dementia-prevention treatment. The latest systematic review does not establish a protective effect, and the
newer UK Biobank findings, although encouraging, are observational and therefore cannot demonstrate causation.
At the same time, it would be an oversimplification to say that HRT simply causes dementia. The evidence from WHIMS relates to an older population starting specific hormone preparations many years after menopause. More recent research in women around the menopause transition has not produced the same clear cognitive-harm signal, while some observational studies suggest that timing may be relevant.
The honest conclusion is therefore that the relationship between HRT and long-term brain health remains an active area of research.
What does this mean for women considering HRT?
For an individual woman, the decision about HRT should not be based on dementia risk in isolation.
A clinician will consider factors such as:
- age and stage of menopause;
- the timing and circumstances of menopause;
- the woman’s symptoms and reasons for considering HRT;
- personal and family medical history;
- cardiovascular and breast health;
- the type, dose and route of hormone therapy being considered; and
- other individual risk factors.
This is particularly important because the potential benefits and risks of HRT extend well beyond cognition.
HRT remains an established treatment for menopausal symptoms, and decisions about treatment should be based on an individual’s overall circumstances rather than on a single study or headline.
The bigger picture
There is still much to learn about the relationship between menopause, oestrogen and the ageing brain.
The research increasingly suggests that the question may not simply be whether HRT is “good” or “bad” for cognitive health.
It may be more nuanced:
Which woman? Which hormones? At what dose? For how long? And, importantly, at what stage of life?
Answering those questions will require further long-term research, particularly studies capable of distinguishing the effects of different formulations and treatment strategies
and determining whether associations seen in observational research translate into genuine reductions in dementia risk. For women, the most useful message is therefore one of context.
HRT and dementia is a complex area of science, and the evidence is evolving. Women deserve information that reflects that complexity rather than a conclusion based on a single study.
At Marion Gluck Clinic, we believe decisions about hormone therapy should be individualised, evidence-led and made in partnership with a qualified clinician, taking into account a woman’s symptoms, medical history, risk factors and treatment goals.
https://www.thelancet.com/journals/lanhl/article/PIIS2666-7568(25)00122-9/fulltext
https://www.medrxiv.org/content/10.1101/2025.07.22.25331871v1.full
