Hormone replacement therapy increases the risk of stroke by almost a third, according to new research published today.

The research team from Nottingham University is advising patients who already have a high risk of stroke to stop taking HRT unless there is a strong medical reason to continue.

The study, based on the results of a review of clinical trials, will add weight to current fears about the safety of the long-term use of HRT, which has also been linked to a higher risk of breast cancer and heart attack.

Researchers reviewed the results of 28 trials involving almost 40,000 patients and concluded that HRT increased the risk of stroke by 29%. One of the trials included in the review was the large US study from the Women's Health Initiative which in 2002 linked HRT with higher risks of breast cancer, heart attack and stroke. The latest review found HRT was associated with a sharp increase in the risk of ischaemic stroke, which is caused by an insufficient blood supply to the brain. The severity of the stroke also increased with HRT use.

The researchers, 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 non-significant increase in fatal stroke."

The researchers, whose study appeared on bmj.com this morning, said it was unclear why HRT should increase the risk of stroke and its severity when some studies had suggested it might have a protective effect.

They said: "We have 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."