The labels for several drospirenone-containing combination oral contraceptives (COCs) sold in the United States  will be updated to contain information about an increased risk for venous thromboembolism (VTE) after an FDA safety review concluded that COCs may VTE risk as much as three-fold compared with other oral contraceptives.

The label changes apply to nine brand-name contraceptives — Beyaz (Bayer), Gianvi (Teva), Loryna (Sandoz), Ocella (Barr Laboratories), Safyral (Bayer), Syeda (Sandoz), Yasmin (Bayer), Yaz (Bayer) and Zarah (Watson) — and two generic formulations, all of which include 3 mg of drospirenone and either 0.02 or 0.03 mg of ethinyl estradiol. Two (Beyaz and Safyral) also contain 0.451 mg of levomefolate calcium.

The labeling changes specifically state that these COCs may be associated with a higher risk of venous thromboembolism (VTE) than COCs containing levonorgestrel or some other progestins. In addition, the revised labels update information that there is a risk of VTE among all COCs, but that the risk of VTE associated with pregnancy is even greater than the risk associated with any COC use, including drosperidone-containing COCs.

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The FDA emphasized that the increased risk of VTE with drospirenone is not definite, as results from the five studies included in the analysis varied.

“The studies reviewed did not provide consistent estimates of the comparative risk of blood clots between birth control pills that contain drospirenone and those that do not,” the agency said in a Drug Safety Communication.

The FDA noted that patient characteristics not accounted for in the studies may also play a role in VTE risk with drosperidone-containing birth control.

The agency released the following clotting risk estimates per 10,000 person years for different groups of women : one to five among pregnant women not using oral contraceptives; three to nine among combination contraceptive users; five to 20 among pregnant women; and 40 to 65 during the 12 week postpartum period.

This article originally appeared on MPR