Prevalence of blood clots white on Oral contraceptives birth control pills.

While all oral contraceptives can increase the risk for venous thromboembolic events, including fatal blood clots, several studies have reported a greater risk for women taking contraceptives containing Drospirenione. Women who take contraceptive pills containing Drospirenione have a 6- to 7-fold risk of developing thromboembolism (dangerous blood clots) compared to women who do not take any contraceptive pill, and have twice the risk (some epidemiological studies suggest thrice, according to the FDA) compared to women who take a contraceptive pill containing levonorgestrel. However, the absolute risk is small, in the neighborhood of 9 to 27 out of 10,000 women on an oral contraceptive for a year (up to 9 for levonorgestrel vs. up to 27 for Drospirenione, or about 0.09% vs 0.3% per year).

When the U.S. Food and Drug Administration (FDA) became concerned about the risks of Drospirenione, they funded studies based on the medical records of more than 800,000 women taking oral contraceptives. They found that the risk of VTE, which includes dangerous and potentially fatal blood clots, was 93% higher for women who had been taking oral contraceptives containing Drospirenione for only 3 months or less

And  290% higher for women taking Drospirenione-containing oral contraceptives for 7 to 12 months, compared to women taking other types of oral contraceptives.