Over the past decade or so, there have been at least 20 prescription drugs removed from the market, including several cases of high-profile blockbuster drugs that were found to be harmful only after millions of patients had taken them. Vioxx, the pain reliever sold by Merck is one example; taken by an estimated 20 million Americans, it increased the risk of heart attack and stroke in some patients. The company ended up paying out a $4.85 billion settlement after the drug was pulled from the market in 2004. The diet drug Meridia, also linked to a higher risk of heart attack and stroke, was on the market for over 12 years before it was withdrawn last year. According to the watchdog group Public Citizen, drugs taken off the market since 1993 were sold for an average 4.1 years before being pulled.