Canadians have launched class-action lawsuits against Bayer Inc., the maker of birth control drugs Yaz and Yasmin, alleging the pills have caused serious health problems.

Health Canada approved Yasmin and Yaz in 2004 and 2008 as oral contraceptives. The pills have been used by thousands of women.

"Our firm has received complaints from dozens of women across Canada who have suffered blood clots, pulmonary embolisms, gall bladder removals and other serious medical emergencies, which our class-action lawsuits allege were caused by Yaz/Yasmin," Tony Merchant Law Group LLP said in a release.

The firm launched a class action in British Columbia on Thursday and similar suits were launched in Ontario and Saskatchewan last year.

Likewise, a statement of claim from Siskinds LLP alleges Bayer failed to adequately warn patients and doctors of the increased risk of serious adverse injuries associated with the use of Yasmin and Yaz, compared with other oral contraceptives.

"We believe that through this lawsuit Bayer will be required to explain to Canadian consumers what it knew about the risks associated with using Yasmin and Yaz and when it first became aware of those risks," Matthew Baer, a lawyer with Siskinds, said in a release Wednesday. The suit has not been court-certified.

Siskinds said marketing for Yaz was targeted at young women with claims of clearer skin and reduced menstrual symptoms.

All birth control pills carry risks. The lawsuits claim Yaz and Yasmin carry higher risks, compared with other combined birth control pills brands, because they contain a new type of progestin called drospirenone.

It is alleged that drospirenone does not sufficiently counterbalance the clotting effects of estrogen, compared with other progestins. Another concern is that drospirenone can cause an increase in potassium levels in the blood. If potassium levels become dangerously high, some studies suggest it can lead to heart rhythm problems.

No difference in risk: Bayer  

The allegations have not been tested in court.

In a statement to CBC News on Thursday, Bayer Inc. said it "has received lawsuits regarding its drospirenone-containing contraceptives. The company is in the process of gathering information on these cases."

Bayer said its oral contraceptives have been and continue to be extensively studied worldwide and, for the vast majority of users, "the benefit-risk profile is favourable when used as directed."

The company said large, independently conducted studies sponsored by Bayer have found no difference in the risk of blood clots with drospirenone-containing oral contraceptives, including Yaz and Yasmin, compared with other oral contraceptives.

More than two million prescriptions for the contraceptives were filled in Canada in 2009, according to IMS Health Canada, a company that tracks prescribing.