Blood clots have been a known risk of oral contraceptives since the 1990s, but for most women, the chances seemed small enough to justify taking the Pill. Now, in a report published in The BMJ,scientists led by Yana Vinogradova, a research fellow at the University of Nottingham, found that using the Pill was linked to anywhere from a two- to more than four-fold increased risk of developing clots compared to women who didn’t take oral contraceptives.

“Our study suggests that the newer contraceptives have a higher risk of [blood clots] than the older agents,” Vinogradova tells TIME in an email. Overall, the risk for women on the Pill was nearly three times that of women not taking the medication. The risk was highest for people taking Pills that contain newer types of the progestogen hormone, such as drospirenone, desogestrel, gestodene, and cyproterone, as compared to people taking the Pill with first-generation versions of the hormone (levonorgestrel and norethisterone).