Blood clot risk, birth control linked

Women who take newer types of birth control pills face a higher risk of developing blood clots than women who take older types, researchers said Tuesday, providing what some called “clarifying” evidence that more modern contraceptives designed as safer options may in fact pose more risk than earlier formulations.

Poring over two medical records databases to study more than 50,000 15- to 49-year-old women in Britain, University of Nottingham researcher Yana Vinogradova and colleagues found, as researchers have known for decades, that women who took combined oral contraceptives (formulations that include versions of two hormones, estrogen and progestin) had a higher risk of developing venous thromboembolisms – dangerous blood clots – than women who don’t take the pill.

But when the team broke out the data by medication and controlled for other risk factors, they also discovered that certain versions of the birth control pill were associated with higher risk than others. Medications using the synthetic hormones drospirenone (found in Yasmin), desogestrel (found in Kariva and Mircette) and other newer formulations were associated with about a 1.5 to 1.8 times higher risk than older drugs containing synthetic hormones such as levonorgestrel.

The team’s study, published Tuesday in the journal the BMJ, confirms past findings, said Susan Jick, an epidemiologist at the Boston University School of Public Health.