Pfizer didn't need to be sued it admtted liability in many cases. Some of the actions against it were by state legislators. But there have been actions about drug side effects and supplying substandard products, like heart valves
In 1994 the company agreed to pay $10.75 million to settle Justice Department charges that it lied to regulators in seeking approval for the valves; it also agreed to pay $9 million to monitor valve patients at Veterans Administration hospitals or pay for removal of the device.
In 2004 Pfizer announced that it had reached a $60 million settlement of a class-action suit brought by users of Rezulin, a diabetes medication developed by Warner-Lambert, which had withdrawn it from the market shortly before the company was acquired by Pfizer in 2000. The withdrawal came after scores of patients died from acute liver failure said to be caused by the drug.
In 2004, in the wake of revelations about dangerous side effects of Merck’s painkiller Vioxx, Pfizer agreed to suspend television advertising for a related medication called Celebrex. The following year, Pfizer admitted that a 1999 clinical trial found that elderly patients taking Celebrex had a greatly elevated risk of heart problems.
In 2005 Pfizer withdrew another painkiller, Bextra, from the market after the FDA mandated a “black box” warning about the cardiovascular and gastrointestinal risks of the medication. In 2008 Pfizer announced that it was setting aside $894 million to settle the lawsuits that had been filed in connection with Bextra and Celebrex.