Actos, the ninth most commonly prescribed drug in the U.S., may double your chances of bladder cancer. Actos belongs to a widely used class of diabetes drugs called thiazolidinediones (TZDs). These drugs total about 20 percent of the drugs prescribed to diabetics in the U.S.

The researchers from the Perelman School of Medicine at the University of Pennsylvania emphasize that their findings are important: People with diabetes are known to already be at increased risk of bladder cancer.

The study analyzed the health records of 60,000 people with type 2 diabetes and showed that patients treated with the TZD drugs pioglitazone (Actos) or rosiglitzaone (Avandia) for five or more years were between two and three times more likely to develop bladder cancer compared to those who took sulfonylurea drugs.

Though most patients in the United States no longer take Avandia since it was linked to cardiovascular complications, Actos is the ninth most commonly prescribed drug in the Nation, accounting for 15 million prescriptions each year. The drug is a common choice when type 2 diabetes patients’ illnesses can no longer be controlled with the first-line diabetes drug Metformin.