Newer pill may cause more clotting

Oral contraceptives are one of the most effective means of preventing an unwanted pregnancy, yet different versions of the Pill carry different risk-benefit profiles. Now, a new study has shed light on what may be a risk for women who use a newer variety of birth control pill that contains the hormone drospirenone, which includes popular brand names like Yaz and Yasmin. Women who used this variety of birth control pill were at greater risk of developing venous blood clots than were women on older, second- and third-generation varieties.

The study looked at 330,000 Israeli women and found that the risk of these blood clots was 43 to 65 percent higher for women who took the newer variety of birth control pill. Yet Dr. Ross observes that the absolute risk for most women is still very small, regardless which version of the Pill they take: While there were just over six cases of venous blood clots per 10,000 users of the older Pill each year in the study, there were eight to 10 clots for every 10,000 women taking pills that contained drospirenone. The study authors also found that the risk of clotting was greatest in the first few months of use, which suggests that women who ve already become comfortable with a regimen of these pills have little reason for concern.

Practically speaking, says ACSH's Dr. Gilbert Ross, the risk of an unplanned pregnancy without birth control pills is still vastly more significant than the risk of a blood clot when a woman is taking an oral contraceptive containing drospirenone. He does point out, however, that some women in particular do need to be more cautious about choosing a birth control pill: Women who smoke and who are older than 35 are at a greater risk for blood clots, and are typically advised to avoid birth control pills altogether. These women, he says, should use barrier methods of contraception instead.