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Evidence of blood-clot risk builds for newer oral contraceptives

A Bayer Schering Pharma employee examines YAZ birth control pills in the company's factory in Berlin, Germany, in this undated handout photo, released to the media on Friday, Jan. 15, 2010.

Matthias Lindner/Via Bloomberg

The future of two of the most widely prescribed birth-control pills in Canada may be in question as more evidence is emerging to suggest that they come with higher risks of blood clots than similar older medications.

A study published on Monday in the Canadian Medical Association Journal found that women who take drospirenone-containing birth-control pills, such as Yaz and Yasmin, face a greater chance of developing potentially serious blood clots in the leg or lung.

The new research comes just days after another study released by the U.S. Food and Drug Administration found that the risk of blood clots was significantly higherin women taking pills containing drospirenone, a type of progestin (a synthetic female sex hormone), compared with those taking older classes of oral contraceptives.

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Two recent studies in the British Medical Journal also reported an increased risk of blood clots from Yaz and Yasmin.

Experts say the overall risk of blood clots for women taking the newer pills is about 3 or 4 in 1,000, compared with about 1 in 1,000 among women taking older-generation contraceptives. But when expanded across an entire population, those risks could affect a large number of women, which is why the findings are prompting growing concerns.

Earlier this year, Health Canada announced that it would conduct a safety review of the two pills, the only ones containing drospirenone on the market in Canada, and last month, the FDA said it will hold a meeting with scientific advisers in December to discuss the safety of the drugs.

But some experts, as well as Bayer, the drug manufacturer that sells Yaz and Yasmin in Canada, dispute the link between newer birth-control pills and higher risk of blood clots.

All birth-control pills are linked to an elevated risk of blood clots, particularly among women who are over 35 or who have certain risk factors, such as smoking or being obese. Deep-vein thrombosis, or a blood clot in the leg or thigh, can cause swelling and pain. But the clot can also break free and travel to the lung, which could lead to serious complications and even death.

The majority of oral contraceptives contain estrogen and progestin. It is believed that the hormones in those pills may increase a woman's risk of developing blood clots. While the overall risks are quite low, research shows that women taking oral contraceptives are more likely to experience them than those who are not taking those pills.

Although researchers aren't sure why, a growing amount of research suggests that newer pills made with drospirenone may increase the incidence of blood clots more than others.

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The potential for serious side effects involving these new pills has attracted a significant amount of attention in the medical community as well as the public because they have become so popular since they came on the market in the past few years. Yasmin was introduced in 2004 and Yaz in 2009; combined, they are more widely prescribed than any other single birth-control pill in Canada

In 2010, about 1.67 million prescriptions for Yasmin were dispensed from retail pharmacies, just slightly less than the top pill, Alesse, which had 1.7 prescriptions last year. At the same time, nearly 620,000 prescriptions for Yaz were filled in 2010, according to IMS Brogan, which tracks the pharmaceutical industry.

The combined value of prescriptions for Yaz and Yasmin in 2010 was nearly $71-million in Canada, IMS Brogan says.

The new CMAJ study, led by researchers based in Israel, focused on about 330,000 women 12 to 50 years old. They found that those taking pills with drospirenone had a higher risk of blood clots, says Naomi Gronich, physician and internist with the pharmacoepidemiology and pharmacogenetics unit at Clalit Health Services in Tel Aviv.

Responding to the study, Bayer said in a statement that the risks associated with using Yaz and Yasmin are comparable to that of other oral contraceptives. "All birth-control pills, including Bayer's, carry an increased risk of blood clots, stroke and heart attack. These serious side effects are rare," it said.

The company also pointed out that it has sponsored several independently conducted studies that have shown that the risks of blood clots from drospirenone-containing pills are similar to that of other birth-control pills.

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The Society of Obstetricians and Gynecologists of Canada said last year that some evidence highlighting the specific risks of drospirenone-containing contraceptives may be flawed and that other studies have found that they carry no increased risk.

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About the Author

Carly Weeks has been a journalist with The Globe and Mail since 2007.  She has reported on everything from federal politics to the high levels of sodium in the Canadian diet. More

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