Oral contraceptives increase the risk of ischaemic stroke, but this risk is very small among women who do not have other stroke risk factors, according to a comprehensive review in the journal MedLink Neurology by Loyola Medicine (Chicago, USA) stroke specialists.
Birth control pills do not increase the risk of haemorrhagic strokes, wrote neurologists Sarkis Morales-Vidal and José Biller. Ischaemic strokes, which account for about 85% of all strokes, are caused by blood clots. Haemorrhagic strokes are caused by bleeding in the brain.
Several mechanisms have been proposed to explain why oral contraceptives increase stroke risk, including by raising blood pressure and by making blood hypercoagulable (more likely to clot).
When prescribing hormonal contraceptives, physicians should consider the type and dose of oestrogen or progestin and route of administration (such as pill or patch). “The ideal drug is one with the lowest oestrogen and progestin doses that will be effective in preventing pregnancy while minimising adverse effects,” Morales and Biller wrote.
For healthy young women without any stroke risk factors, the stroke risk associated with oral contraceptives is very small.
“However, in women with other stroke risk factors, the risk seems higher and, in most cases, oral contraceptive use should be discouraged,” Morales and Biller wrote. These risk factors include high blood pressure, cigarette smoking and migraine headaches, especially migraines with sensory disturbances called aura (such as flashes of light and tingling in the hands or face).
However, women may not always be adequately screened. One previous study found that, among women with one or more stroke risk factors, only 15% recalled being advised not to start oral contraceptives and only 36% remembered being told to stop. Fifteen percent of women were still taking oral contraceptives despite being told to discontinue. These findings highlight the need to improve physician advice and patient compliance, Morales and Biller wrote.