Non-smokers who don't suffer from migraines have a much lower risk if they're on the pill, but it still increases the risk of ischaemic stroke by 80 per cent, say researchers from Brigham and Women's Hospital in Boston.
Another risk is high blood pressure (hypertension)—and women with two or more of these risk factors should seriously consider stopping the birth control pill, they add.
An earlier study had concluded that the pill didn't increase stroke risk—but this was only for haemorrhagic stroke, which happens when there's bleeding in the brain. But ischaemic stroke—which occurs when an artery in the brain gets blocked—is by far the more common type of stroke, accounting for 85 per cent of all cases. In the US, 55,000 more women than men suffer a stroke every year. Hormones and longevity are other reasons for the disparity, the researchers say.