Bayer said that the company had been served with 74 lawsuits brought by women who charge that they developed health problems after taking Yaz or Yasmin. The company says it intends to defend itself vigorously against the suits.

The health questions and the lawsuits may rattle consumer confidence, but the warnings from federal health authorities about advertising and quality control raise larger questions about Bayer’s approach to complying with government rules, said Michael A. Santoro, an associate professor at the Rutgers Business School who has studied ethics in the pharmaceutical industry.

Birth control pills work by altering a woman’s hormone levels. Researchers have long known that taking a combination hormone birth control pill  which contains estrogen and a progestin hormone  can increase the risk of stroke and blood clots in the legs and lungs. That is because estrogen can play a role in blood coagulation. Indeed, since the introduction of oral contraceptives in the 1960s, drug companies have greatly reduced estrogen doses to decrease the risk of thrombosis, the medical term for blood clots.

With lower-dose estrogen pills now available, the safety debate, continuing for the last decade, has focused on whether the type of progestin in a formula may also play a role in the risk of cardiovascular problems.

In 2001, the F.D.A. approved Yasmin, which contains a novel progestin called drospirenone.

Yaz, which contains drospirenone and a lower dose of estrogen, received agency approval in 2006. For women seeking contraception, the drug is also approved to treat severe emotional and physical symptoms called premenstrual dysphoric disorder and for moderate acne. Because drospirenone can increase potassium levels in the body, it may put women who have liver or kidney problems at risk for serious heart problems, according to the drug label.

Studies on the safety of birth control pills have reported different results on the risks of progestins.

Image Anne Marie Eakins is suing Bayer, saying that she developed blood clots in her lungs after taking Yaz. Labels for Yasmin and Yaz by Bayer contain warnings about the risk of side effects like blood clots and strokes. Credit... David Maxwell for The New York Times

One large-scale study in Europe, sponsored by Bayer, reported that there was no difference in the risk of cardiovascular problems or death in women taking drospirenone birth control pills compared to women who took pills that contained levonorgestrel, a progestin that has been used since the 1970s.