Is HRT safe? The 2002 study and what changed since

Where the fear came from

In 2002, early results from the Women's Health Initiative study were reported and widely covered. Prescribing fell sharply across the world, and a generation of women were taken off treatment or never offered it.

Two things about that study matter now. The average participant was in her sixties, well past menopause, so the findings were not drawn from the women most likely to be offered HRT for symptoms today. And the preparations used were oral, using hormone types that are not what is typically prescribed in the UK now.

The findings have been substantially reanalysed over two decades, and guidance has been rewritten.

That does not mean the risks were invented. It means they were reported without the qualifiers that turn out to matter enormously.

What the risks actually are

Blood clots. Oestrogen taken by mouth is associated with an increased risk of venous thromboembolism. Oestrogen delivered through the skin is not associated with that increased risk. This is one of the clearest distinctions in the evidence, and it is why UK guidance recommends the transdermal route for women at increased risk, including women with a BMI over 30.

Breast cancer. Combined HRT is associated with a small increase in breast cancer risk that relates to duration of use, and which reduces after stopping. The size of that risk appears to depend on the type of progestogen. A meta-analysis has found that oestrogen combined with micronised progesterone is not associated with an increased risk in the first five years. Beyond five years the evidence is thinner, and duration still matters. Oestrogen-only HRT, used by women who have had a hysterectomy, carries little or no increased risk.

For context, the British Menopause Society and Women's Health Concern make a comparison in their own patient information: the effect of combined HRT on breast cancer risk is broadly comparable to everyday factors such as being overweight, or drinking a couple of units of alcohol a day. That is not a reason to dismiss it. It is a reason to weigh it properly rather than treat it as categorically different.

Womb cancer. Oestrogen alone thickens the womb lining and raises this risk, which is precisely why progesterone is included for every woman who still has a womb. Taken correctly, that protection is the point.

Stroke. A small increased risk is associated with oral oestrogen. Transdermal preparations at standard doses are not associated with increased stroke risk.

What the benefits are

Effective relief of vasomotor symptoms, which is what most women start for. Improvement in sleep, mood and genitourinary symptoms. Protection against the bone loss that accelerates around menopause.

For women with premature ovarian insufficiency, treatment until the usual age of menopause is generally recommended rather than optional, because the risks of prolonged oestrogen deficiency at a young age are significant.

Who needs a proper conversation first

• Current or previous breast cancer or other oestrogen-sensitive cancer
• Previous blood clot, or a known clotting disorder
• Liver disease
• Unexplained vaginal bleeding, which needs investigating before anything is prescribed
• Uncontrolled high blood pressure

None of these means the answer is automatically no. Each means the decision needs a clinician with your history in front of them.

Why timing matters

The evidence is more favourable for women starting near the time of menopause, generally under 60 or within ten years of menopause, than for women starting many years later. That is sometimes called the window, and it is one reason not to spend three years deciding.

What this page cannot tell you

Whether HRT is safe for you.

"Most healthy women" is a population statement. Your history is not a population. That is the entire reason our assessment exists and the entire reason it comes before anything is sold: a free, structured review of your symptoms, history and contraindications, read by a UK-registered prescribing clinician who either prescribes or does not.