Health Canada is reviewing two new studies that show Yasmin, the country's top-selling birth control pill, may put women at a higher risk of blood clots, CBC Marketplace has learned.

The studies were published in the British Medical Journal last month and report that women taking birth control pills containing drospirenone have 2.5 to three times the risk of suffering a blood clot than women on the safest pills on the market.

Most birth control pills contain progestin and estrogen, but only a handful use the synthetic hormone drospirenone for the progestin, including Yasmin and its sister pill, Yaz, which are manufactured by German-based Bayer.

Assessing risks

In an email to CBC Marketplace, a Health Canada official said the department "is evaluating the recently published studies and is looking at available information to fully assess the risk of blood clots."

The email also said Health Canada is reviewing an announcement made May 27 by the European Medicines Agency that it is updating the product information accompanying oral contraceptives containing drospirenone to inform consumers of the increased risk with Yasmin and Yaz.

For now, however, Health Canada said it "considers that the benefits outweigh the risks when drospirenone-containing contraceptives are used as directed in the Canadian Product Monograph."

Health Canada's review comes on the heels of an announcement this week by the U.S. Food and Drug Administration that it, too, is reviewing new research that raises concerns about birth control pills containing drospirenone.

The FDA safety review covers all oral contraceptives made with drospirenone and will look at the risk of blood clots to women using those products.

Growing concern about drospirenone

All birth control pills carry a small risk of blood clots, but as CBC Marketplace reported earlier this year in Spinning a Pill, there are growing concerns about pills made with drospirenone.

Previous studies looking at blood clots for women taking pills containing drospirenone had conflicting findings. Two reported an increased risk of blood clots, while two — funded by Bayer — found no difference. Now, the FDA has commissioned an additional large study looking at all birth control pills and blood clot risk.

Women interviewed by CBC Marketplace said they wished they had known there was a small but significant increase in the risk of blood clots for those taking Yasmin and Yaz.

Class action lawsuits in Canada and the United States allege that drospirenone birth control pills lead to an increased risk of blood clots. Thousands of women have reported serious health issues, including pulmonary embolisms, after going on those pills. In some cases, deaths have been reported.

Bayer says its drospirenon-containing birth control pills Yasmin and Yaz carry no greater risk of blood clots.