Birth control pills pose small but significant stroke risk

Birth control pills cause a small but significant increase in the risk of the most common type of stroke, according to a comprehensive report in the journal MedLink Neurology.

For healthy young women without any stroke risk factors, the risk of stroke associated with oral contraceptives is small. But in women with other stroke risk factors, "the risk seems higher and, in most cases, oral contraceptive use should be discouraged," report co-authors Marisa McGinley, DO; Sarkis Morales-Vidal, MD; and Jose Biller, MD of Loyola University Medical Center and Loyola University Chicago Stritch School of Medicine.

Worldwide, more than 100 million women currently use oral contraceptives or have used them in the past. In the United States, there are about 40 brands of oral contraceptives and 21 brands of emergency contraceptive pills.

Strokes associated with oral contraceptives were first reported in 1962. Early versions of the pill contained doses of synthetic estrogen as high as 150 micrograms. Most birth control pills now contain as little as 20 to 35 micrograms. None contain more than 50 micrograms of synthetic estrogen.

Oral contraceptives increase the risk of ischemic strokes, which are caused by blood clots and account for about 85 percent of all strokes. In the general population, oral contraceptives do not appear to increase the risk of hemorrhagic strokes, which are caused by bleeding in the brain.

There are about 4.4 ischemic strokes for every 100,000 women of childbearing age. Birth control pills increase the risk 1.9 times, to 8.5 strokes per 100,000 women, according to a well-performed "meta-analysis" cited in the report. (A meta-analysis combines the results of multiple studies.) This is still a small risk; 24,000 women would have to take birth control pills to cause one additional stroke, according to the report.

But for women who take birth control pills and also smoke, have high blood pressure or have a history of migraine headaches, the stroke risk is significantly higher. Such women should be discouraged from using oral contraceptives, the report said.

Hormone replacement therapy with estrogen alone or combined with progesterone increases the risk of ischemic stroke by 40 percent; the higher the dose, the higher the risk, the report said.