Researchers with Loyola University Health Center say taking oral contraceptives doubles a woman’s risk for having a stroke.

Eight and a half women out of 100,000 who take the pill will have a stroke, according to the study’s results. Although researchers say the risk is low, they stress that having additional stroke risk factors make them significantly more vulnerable. Those risk factors include smoking, high blood pressure and migraine headaches.

"When prescribing oral contraceptives, doctors should balance the risks and benefits for each individual patient. For a healthy young woman without any other stroke risk factors, the benefits of birth control pills probably outweigh the risks. But if a woman has other stroke risk factors, she should be discouraged from using oral contraceptives," said senior author Dr. Jose Biller.

How oral contraceptives might cause strokes is not completely understood. Researchers say the increased risks of blood clots and high blood pressure associated with oral contraceptives may be to blame.

Nearly 100 million women worldwide use oral contraceptives. The medical community has debated whether or not they increase stroke risk for years with conflicting results.

Among the best ways to prevent strokes are controlling hypertension, avoiding smoking, eating a healthy, low-fat diet and exercising, according to the National Stroke Association.