A U.S. review of different studies indicated that oral contraceptives can double the risk of stroke. But, the actual reasons behind the link between increased risk of stroke and oral contraceptive are not yet completely understood.

However, the authors of the study believe that the increased risks of blood clots and high blood pressure link with oral contraceptives could be the possible reason.

Dr. Jose Biller, Dr. Michael J. Schneck and Dr. Sarkis Morales-Vidal, all Loyola University Health System neurologists, say oral contraceptives used today contain much lower concentrations of estrogens than older preparations.

The review indicated that there were 4.4 ischemic strokes for every 100,000 women of childbearing age, but birth control pills increased 4.4 ischemic strokes to 8.5 strokes per 100,000 women. Hence, the stroke risk is almost doubled.

Moreover, the risk of stroke is highly increased for those women who take birth control pills and smoke along with high blood pressure or a history of migraine headaches.

Study authors warn that possible risks and benefits associated with the use of oral contraceptives should be properly analyzed and compared with other forms of contraception.