Millions of women use oral contraceptive to prevent unwanted pregnancy but findings of a new study have shown that birth control pills can slightly elevate the risks for stroke.

While the risk is relatively weak for women who do not have risk factors for stroke, it increases for those who already have higher odds of having one.

For the new study published in MedLink Neurology, researchers conducted a meta-analysis of earlier studies that have associated contraceptive pills with increased risks for heart attack, migraine and stroke.

The analysis revealed that birth control pills raise the risks for stroke by 1.9 times which is equal to one additional stroke for every 25,000 women who uses birth control pills.

The risk is higher in women who use birth control pills and also smoke, have history of migraine, or have high blood pressure. The researchers said that these women should not take contraceptive pills.

The risks of serious side effects appear to be higher in women who take over 50 mcg of estrogen albeit birth control pills that are available today no longer have over 50 micrograms of synthetic estrogen. Some contain as little as 20 micrograms.

About 4.4 ischemic strokes, which are caused by blood clots and make up about 85 percent of all strokes, occur for every 100,000 women who are in their childbearing age.

Oral contraceptives appear to somehow play a role in ischemic strokes albeit they do not seem to contribute to hemorrhagic strokes, which are caused by bleeding on the brain.

"For a healthy young woman without any other stroke risk factors, the benefits of birth control pills probably outweigh the risks," said Jose Biller, from Loyola University Health System. "But if a woman has other stroke risk factors, she should be discouraged from using oral contraceptives."

It is not clear how oral contraceptive might lead to strokes but the researchers pointed out blood pressure and increased risks of blood clots linked with birth control pills as potential factors. Other studies also linked use of contraceptive pills to multiple sclerosis (MS) and breast cancer.

Nearly 100 million women use contraceptive pills worldwide. The U.S currently has about 40 brands of birth control pills and 21 brands of emergency contraceptive pills.

The U.S. Centers for Disease Control and Prevention (CDC) said that the effectiveness of birth control pills along with contraceptive shot, patch and ring as well as fertility awareness-based and barrier methods, depends on consistent and correct use so these are considered less effective compared with intrauterine contraception and the contraceptive implant.

Photo: Iain Watson | Flickr

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