Last week, the first of what many predict will be thousands of lawsuits were filed against the maker of the popular diabetes drug, Actos. More specifically, the lawsuits allege that Actos triggered the development of bladder cancer, in some cases fatal, in patients taking the drug on a daily basis for years.

Takeda Pharmaceuticals, manufacturer of the blockbuster drug, has been facing an onslaught of mounting legal challenges since news broke that taking their popular diabetes pill for more than a year could raise the risk of bladder cancer. Sales of the drug were halted in Europe, following pressure from regulatory agencies, but the U.S. Food and Drug Administration allowed sales of Actos to continue. In fact, the FDA simply issued a warning about the risks associated with use of the drug and reported that the risk of bladder cancer was 40% higher for patients taking Actos for more than a year.

Despite the drug’s link to serious side effects, Actos became the No. 1 selling diabetes drug, following the news that its only competitor, Avandia, was found to drastically increase the risk of heart attacks. Avandia was eventually banned in Europe and heavily restricted in the U.S., and as such, sales of Actos grew from almost $3 billion in 2006 to more than $4 billion in 2010. Given the legal battles currently on the horizon for Actos, those billions may very well shift again, to the pockets of Takeda’s rivals.

The increased risk for bladder cancer is a huge blow to diabetes patients, as Actos was a means by which patients could properly control their blood sugar with very few side effects. Going forward, patients suffering from diabetes and their doctors will have to carefully evaluate their future treatment.