HRT Risks: What the Numbers Actually Say

NICE, the NHS and the largest breast cancer meta-analysis all describe the same pattern.

HRT (hormone replacement therapy) is oestrogen, plus a progestogen if you still have a womb, taken to replace the hormones your ovaries stop making around menopause. The figures below come from NICE guideline NG23, updated in April 2026, from the NHS HRT pages, and from the 2019 individual-participant meta-analysis by the Collaborative Group on Hormonal Factors in Breast Cancer, which included 108,647 women who developed breast cancer.

What are the real risks of HRT?

Risk is not one number. NICE lists nine health outcomes and finds most of them unchanged, or changed only very slightly, by HRT. The exceptions cluster in two places: breast cancer with combined HRT, and clots and stroke with oral oestrogen.

So the useful question is not "is HRT risky" but "which HRT, for how long, and for whom". A 52-year-old with no risk factors and a 66-year-old who has had a clot face different decisions from the same packet.

Absolute numbers make this easier to think about. "A 60% higher relative risk" sounds alarming. "A few extra cases per 1,000 users" sounds like what it is. Where a source states the absolute version, this guide uses it.

How big is the breast cancer risk with HRT?

The NHS puts it plainly: around 5 extra cases of breast cancer in every 1,000 women who take combined HRT for 5 years. The risk rises the longer you take it, and it falls again after you stop.

The 2019 meta-analysis turns that into rates by preparation. For women of average weight starting HRT at 50, five years of treatment would increase breast cancer incidence between ages 50 and 69 by:

• about 1 in 50 users of oestrogen plus daily progestogen
• about 1 in 70 users of oestrogen plus intermittent progestogen
• about 1 in 200 users of oestrogen alone

Ten years would roughly double those excesses. The same analysis found that some excess risk persists for more than 10 years after stopping, depending on how long you took it.

NICE adds three qualifications that matter in a consultation:

• Sequential combined HRT carries lower breast cancer risk than continuous combined HRT, but still higher than no HRT.
• Oestrogen-only HRT has very little or no increase in breast cancer risk, and little or no increase in breast cancer deaths.
• There is not enough evidence to say whether micronised progesterone or dydrogesterone differ from other progestogens. Anyone who tells you they are proven safer is going beyond the guidance.

Vaginal oestrogen is the exception the meta-analysis singles out: every other type raised risk, vaginal oestrogen did not. It is a low-dose local treatment.

Do HRT tablets increase the risk of blood clots?

Yes, if the oestrogen is swallowed. NICE states that venous thromboembolism risk is increased with oral HRT, is not increased with transdermal HRT, and is greater with oral than transdermal.

Venous thromboembolism means a clot in a deep vein or in the lung. It is the risk that most often decides which type of HRT you are offered. Ask for a patch, gel or spray if any of these apply to you:

• you have had a clot, or a parent or sibling had one before 45
• you have a high body mass index
• you are immobile for long periods, or have surgery planned
• you carry a clotting variant such as Factor V Leiden

Tell your prescriber before surgery or a long flight, and ask whether to pause or change treatment. A clot risk that is manageable on a patch is a reason to change the route, not to give up on treatment.

Can HRT cause a stroke or a heart attack?

Route matters here too, and the difference is larger than most people expect.

• Life expectancy: NICE's guideline, updated in April 2026, says taking either combined or oestrogen-only HRT is unlikely to affect life expectancy.

That last point is the one most people have never been told. It also explains why the guidance changed.

HRT risks compared: combined, oestrogen-only and route

The table summarises NICE's position. The route of oestrogen is read across the rows, so a patch and a tablet do not score the same even in the same column.

What about womb cancer, ovarian cancer, dementia and type 2 diabetes?

Womb cancer. Oestrogen on its own thickens the lining of the womb and raises endometrial cancer risk. That is why anyone with a womb is given a progestogen with it. NICE's discussion aid, which accompanies NG23, puts the five-year figures at about 4 cases per 1,000 women who take no HRT: continuous combined HRT lowers that to about 1, sequential combined HRT raises it to about 8, and oestrogen alone raises it to about 11. Sequential combined HRT may therefore slightly raise the risk, more so with longer use, fewer progestogen days per cycle and higher oestrogen doses. Never take oestrogen alone if you have a womb.

Ovarian cancer. Risk increases very slightly with combined HRT and with oestrogen-only HRT, and rises with duration of use. NICE's discussion aid gives the absolute version: about 1 extra case per 1,000 women over five years, from a baseline of 1 to about 2 per 1,000. Because the baseline risk in women under 60 is very low, that is a small change, but it is real and NICE states it.

Dementia. Combined HRT started at 65 or over might increase dementia risk. NICE's discussion aid estimates about 9 extra cases per 1,000 women over four years when combined HRT is started at 65 or over (about 18 per 1,000, against 9 per 1,000 who take no HRT). Oestrogen-only HRT is unlikely to increase it. HRT is not a way to prevent dementia, and starting it for that reason is not supported.

Type 2 diabetes. HRT does not increase the risk of developing type 2 diabetes, by any route. NICE gives no absolute figure for this outcome because it finds no increase to express.

Why the 2002 warnings still dominate the conversation

The Women's Health Initiative trial reported in 2002 that women taking combined HRT had more breast cancer, heart attacks, strokes and clots. Headlines followed, prescriptions fell sharply, and a generation was told that HRT was dangerous.

The trial's participants were mostly in their sixties, many years past menopause, and it tested one combination at one dose. Applying those results to a 51-year-old starting treatment for hot flushes was never sound.

The NHS now describes that older reading as out of date, because it weighed the risks without the benefits. NICE's guideline, updated in April 2026, is more specific still: no increase in heart disease, no change in life expectancy, and transdermal routes that avoid the clot and stroke signal.

What survives is a narrower caution. Combined HRT and breast cancer. Oral oestrogen and clots or stroke. Combined HRT started in your mid-sixties and dementia. Those are the conversations worth having, and they are all about your own circumstances.

How can you lower your HRT risks?

Most of the levers are in the prescription and the review, not in willpower.

• Ask whether transdermal oestrogen suits you. It avoids the clot risk and the oral stroke signal, and it is the standard choice if you have any vascular risk factor.
• Use the lowest dose that controls your symptoms. NICE recommends discussing dose and duration as part of the original decision.
• Review at least once a year. NICE recommends rediscussing benefits and risks at every review, and reviewing the planned duration of treatment.
• Do not stop at an arbitrary age. Discuss duration instead, and know that symptoms may return if you stop and that you can restart.
• Attend every breast screening appointment. HRT makes screening more important, not less.
• If you only have vaginal dryness, ask about vaginal oestrogen. It does not carry the systemic risks described here.

What side effects are common but not dangerous?

Progestogen side effects are common: bloating, breast tenderness, headaches and low mood. They often settle after the first few months, and changing the progestogen, the dose or the schedule often fixes them.

Oestrogen can cause nausea, breast tenderness and leg cramps. Patches sometimes irritate the skin, and rotating the site helps.

These are nuisances rather than the risks above. Report them, because they are treatable, but they are not a reason to accept untreated symptoms.

Unscheduled vaginal bleeding is common in the first 6 months of systemic HRT, or within 3 months of changing the dose or preparation. NICE advises seeking medical help promptly if it continues beyond those windows.

When to see a doctor:

• A new breast lump, nipple discharge, or a change in the skin or shape of a breast.
• Painful swelling in one calf, sudden breathlessness, or chest pain, which can signal a clot.
• Sudden face droop, arm weakness or slurred speech: call 999, do not wait for an appointment.
• Any vaginal bleeding after 12 months without a period, or unexpected bleeding on continuous combined HRT after the first 6 months.
• A new or worsening severe headache, or a migraine with aura that has changed.
• A blood pressure reading above your usual range, or surgery being planned, so your HRT can be reviewed first.