The announcement Thursday comes a day after the release of a study in BMJ that also found newer birth control pills were tied to a higher risk for clots.
In that study, researchers reviewed data on all Danish women, aged 15 to 49, who were not pregnant between January 2001 and December 2009. During that time, more than 4,200 first episodes of VTEs occurred.
Women taking birth control pills with a newer progestin hormone had twice the risk of clots compared to those who took the older form of contraceptive pills.
Compared to women who did not use birth control pills, the risk of VTE was three times higher among those who used pills with levonorgestrel and six times higher among those who took pills with drospirenone, desogestrel or gestodene.
But the absolute risk of VTE associated with taking the newer pills remained relatively low, about 10 per 10,000 women, according to the University of Copenhagen researchers.
For every 2,000 women who switched from using newer pills to pills with levonorgestrel, there would be one less case of clots a year.
While some doctors may choose to prescribe birth control pills with a lower risk whenever possible, it is crucial not to exaggerate the risk of VTE, Dr. Philip Hannaford of the University of Aberdeen in Scotland, wrote in an accompanying editorial in the journal.
"Oral contraceptives are remarkably safe and may confer important long-term benefits in relation to cancer and mortality," he said in a journal news release.
Dr. Glenn Jacobowitz, vice chair of the division of vascular surgery at NYU Langone Medical Center in New York City, said: "The information for Yaz is not new. That has recently already been shown in studies to have an increased risk of blood clots t
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