HORMONE replacement therapy increases the risk of stroke by almost a third, and the risk of fatal or disabling stroke by more than half, a review of clinical trials has shown.

In the past, HRT was believed to protect against heart disease and stroke, but with more trials the balance of evidence has shifted. Most experts do not recommend the use of HRT except for brief periods, and the new analysis, which pools the results of 28 trials involving nearly 40,000 women, is likely to discourage many more.

The results, published on the online version of the British Medical Journal, show that strokes are increased by 29 per cent in women on HRT. The effect is seen in ischaemic strokes, caused by blockages of blood flow to the brain, not in the less common form of haemorrhagic stroke, caused by bleeding within the brain.

Fatal or disabling strokes are increased by 56 per cent in women on HRT, while minor and transient stokes that do less long-term damage are not affected. The team, from the University of Nottingham, said that patients with a high risk of stroke should stop taking HRT unless there is a strong medical reason not to.

The trials reviewed included a US study from the Women’s Health Initiative that in 2002 linked HRT with higher risks of breast cancer, heart attack and stroke. Last year the study, which involved almost 17,000 women over 50, said that those taking HRT for five years doubled the risk of life-threatening blood clots.

The Royal College of Obstetricians and Gynaecologists has advised that HRT should be used only in the short term to relieve menopausal symptoms.

The team, led by Professor Philip Bath, said: “A poor outcome after stroke, judged as combined death and dependency, was increased by half with hormone replacement therapy. We also found a significant increase in non-fatal stroke.”

They said it was not clear why HRT should increase the risk of stroke and its severity.

The review will raise further concerns among women seeking treatment for symptoms of the menopause, which include debilitating hot flushes, insomnia, headaches and irritability.

The number of prescriptions for HRT has fallen as more trials have emerged highlighting dangers. But experts say that in the short term the benefits can outweigh the risks because of improvements to quality of life with the relief of severe menopausal symptoms.

The researchers said: “We found that the use of hormone replacement therapy is associated with an increased risk of stroke, typically ischaemic in type and severe in nature.

“HRT cannot be recommended for the primary or secondary prevention of stroke.

“Extrapolation of the data suggests that patients at high risk of stroke — such as those with previous stroke, coronary heart disease or multiple vascular risk factors — should stop taking it unless there is a strong contrary medical reason.”

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