It's true. Look at the fiasco Merck went through a few years back when Vioxx was determined to increase the risk of cardiac episodes. They voluntarily pulled it and suffered major financial setbacks. (Celebrex, a Pfizer product in the same class and with the same side effects as Vioxx, is still on the market and is still widely used.)

More recently, the FDA actually pulled Zelnorm from the market when it was found to cause "severe cardiovascular risks."

Most of the time, the amount of R&D that goes into these meds just isn't enough to determine long term side effects, which effectively turns the patients being prescribed the medication into guinea pigs.