Health Canada has asked drug giant Bayer to change the labels on two popular brands of birth control pills after it concluded use of the medications is linked to higher rates of blood clots than seen with older brands of the pill.
The move comes as the drugs are about to undergo scrutiny from the U.S. Food and Drug Administration because of studies that suggest the drugs are associated with higher rates of blood clots among users.
The drugs — sold as Yasmin and Yaz — were heavily promoted as having fewer side-effects than older birth control brands as well as for their ability to clear up acne and other hormonal concerns.
Health Canada began the review earlier in the year after the British medical journal BMJ published studies that raised safety concerns about birth control formulations that contain the drug drospirenone. Yasmin and Yaz are the only oral contraceptives containing drospirenone that are sold in Canada.
On Monday, Health Canada issued a statement saying that its review of safety data for the drugs suggests women using them may be at a 1.5-to-three fold increased risk of experiencing a clot compared to women using other birth control drugs.
The department said the labels for the two drugs have been updated to reflect the increased risk.
Blood clots are a rare but well known side-effect associated with all birth control pills. Though blood clots can be treated, untreated clots can result in the loss of a limb, if that is where the clot is located. Clots that break free and travel to the heart or lung can kill.
In a carefully worded statement Bayer Inc. contested the suggestion its birth control pills pose a higher clotting risk to women.
Bayer's statement, signed by Dr. Shurjeel Choudhri, senior vice-president for medical and scientific affairs, said the company's own studies show a clot risk for Yasmin and Yaz that is in line with other oral contraceptives.
It suggested the studies published in BMJ had "significant methodological issues... that raise important questions about the validity of the conclusions drawn by the authors."
Bayer won't say how much it earns in sales of Yasmin and Yaz in Canada.
Health Canada did not urge women to stop using Yasmin and Yaz, saying only that women and their doctors should discuss the risks and benefits of drospirenone-containing oral contraceptives in the context of each individual's risk of developing blood clots.
The latest analysis from the FDA estimates the increased risk of clots from drosphirenone-based drugs at 1.5 times the risk of the older oral contraceptives, the low end of the Health Canada estimate.
The U.S. drug regulator explained that figure in terms of cases per 10,000 women, suggesting they would expect to see 10 blood clots in women taking contraceptives containing drospirenone, compared to six in 10,000 cases among women on the other drugs.
Class action lawsuits related to the drugs have been filed in both Canada and the United States by women who say they have experienced serious health problems after taking Yasmin or Yaz.
—With files from The Associated Press