Findings from studies completed by the British Medical Journal and the U.S. Food and Drug Administration (FDA) add to evidence linking oral contraceptives to a higher risk of blood clots, strokes, and pulmonary embolisms in women.

These contraceptives—which include Yaz® and Yasmin®, America’s highest selling birth control since 2006—contain a synthetic hormone drospirenone, which has been discovered to marginally increase the risk of blood clots in its users. The increased risk suggested by the studies is about two to three times more than those from older contraceptives.

Studies show that drospirenone, which is similar in chemical makeup to any popular diuretic, can cause significantly increased potassium levels due to its interference with normal kidney functions. When the kidney function is stalled, potassium builds in the bloodstream. Too much potassium, called hyperkalemia, can lead to cardiac arrest, death, and the formulation of blood clots.

While the report recognizes all birth control contraceptives contain risk for blood clots, the use of drospirenone in drugs such as Yaz and Yasmin has further increased the risk of blood clots forming in a deep vein in the body, a potentially fatal condition known as deep vein thrombosis (DVT).

DVT, a rare birth control pill side effect, could block blood flow and increase the risk of a pulmonary embolism, which has potential for deadly consequences. A pulmonary embolism is often caused by a blood clot in the leg breaking loose, traveling to the lungs. Each year, more than 300,000 people develop DVT or pulmonary embolisms.

Yaz also is linked to heart attacks. Not only does the blood clotting risk increase the chances of heart attacks from Yaz, but also the drug’s link to dangerously high potassium is an extreme emergency because it can cause the heart to stop suddenly. The symptoms are fairly nonspecific, including muscle weakness, malaise, and heart palpitations. Because of these risks, Yaz should not be taken if you have kidney failure, one kidney, liver disease, adrenal disease, or a history of blood clots. Some drugs—such as ibuprofen, high blood pressure medicine, and certain diuretics—can have serious interactions with Yaz and cause hyperkalemia.

An additional report published by the FDA further supports the BMJ findings, revealing that of 800,000 women analyzed, there is a 75 percent increased risk of blood clots in Yaz users when compared to other oral contraceptives. In response to these findings, Bayer—manufactures of Yaz and Yasmin—began updating packaging labels to properly warn consumers of the health risks associated with the drug. Reflecting this body of evidence, the new labels now state:

A prospective cohort study (EURAS1), conducted in Europe, showed the risk of thromboembolism (particularly venous thromboembolism) and death in Yasmin users to be comparable to that of oral contraceptive preparations, including those containing levonorgestrel.
Another prospective cohort study (Ingenix2), conducted in the USA, also showed a comparable risk of thromboembolism in Yasmin users compared to users of other COCs, including those containing levonorgestrel. In this study, COC comparator groups were selected based on having similar characteristics to those being prescribed Yasmin.
Prior to the release of amended warning labels, lawsuits had been filed against Bayer for unlawfully promoting the drug by concealing side effects, including blood clots, heart attacks, and pulmonary embolisms in Yaz users.

So far, the FDA has received hundreds of reports of injury or death among women taking Yaz or Yasmin. The Institute for Safe Medicine Practices also reported that Yaz and Yasmin ranked second in 2011 for the number of complications reported to the FDA.