This US poster warns of the risk and urges pill users not to smoke. Thrombotic stroke, also called occlusive or ischemic stroke, occurs when the flow of blood in the brain is blocked. Hemorrhagic stroke occurs when a blood vessel in the brain ruptures. The most common stroke in women of reproductive age is subarachnoid hemorrhage, in which blood from the ruptured vessel enters the space below the brain's arachnoid membrane and spreads through cerebrospinal fluid passageways. The more recent studies provide more information on ischemic stroke than on hemorrhagic stroke.
Lower doses appear to have reduced the risk.
The multicenter WHO study the largest case-control study of stroke and OCs by far found an overall relative risk of ischemic stroke of about 3 among OC users. Current OC users who did not smoke, had their blood pressure checked, and did not have high blood pressure were at 1.5 times greater risk than nonusers. In contrast, OC users who smoked faced a higher risk about two times greater than among nonsmoking OC users in the developing countries studied and about 3.5 times greater in Europe. Current OC users with a history of hypertension faced the greatest risk about five and four times greater than for other OC users. The WHO study produced conflicting findings on the relationship between dosage and ischemic stroke risk.