(PhysOrg.com) -- Two new drug safety studies conducted by researchers at Boston University School of Medicine (BUSM) provide strong evidence that women taking oral contraception with drospirenone have an increased risk of nonfatal venous thromboembolism, or blood clots, compared to women taking oral contraception with levonorgestrel.
The two studies were led by Susan S. Jick, D.Sc., director of the Boston Collaborative Drug Surveillance Program at BUSM and professor of Epidemiology at Boston University School of Public Health. The results are published in the British Medical Journal.
A number of studies examining the risk of nonfatal blood clots in women taking oral contraception containing drospirenone have recently been published, but, according to Jick, have had limitations. The previous studies did not take into account women who had additional risk factors for blood clots, including a recent surgery, pregnancy or lower limb injury. Additionally, some of the other studies did not take into account previous instances of blood clots.
"When doing research to understand drug safety, certain methods need to be used, and our study addressed the limitations of the others," said Jick.
Jick and her colleagues conducted the two studies simultaneously using two different data resources - one from the United Kingdom and the other from the United States. In both studies, participants were women between the ages of 15 and 44 who had received drospirenone-containing or levonorgestrel-containing oral contraception and had not experienced a blood clot before, nor did they have additional risk factors.
The UK study found that women taking drospirenone contraception had a three-fold higher risk of non-fatal blood clots compared with women taking levonorgestrel contraception. In the study examining women in the US, women taking drospirenone contraception had double the risk of non-fatal blood clots compared with women taking levonorgestrel contraception.
"Our data clearly shows an increased risk in women taking drospirenone contraceptives compared to levonorgestrel contraceptives," said Jick. "It is important for women to be informed about the risks and benefits of the different oral contraceptives so they can make informed decisions."
Explore further: Newer oral contraceptive as safe for gall bladder as older birth-control pills: research