Docs warn of dangers of misusing pain reliever Accidental poisonings from the nation's most popular pain reliever seem to be rising, making acetaminophen the leading cause of acute liver failure. Use it correctly and acetaminophen, best known by the Tylenol brand, is one of the safest painkillers, doctors say. It's taken by some 100 million people a year, and liver damage occurs in only a small fraction of users. But it's avoidable damage that can kill or require a liver transplant, frustrated liver specialists say. The problem comes when people don't follow dosing instructions - or unwittingly take too much, not realizing acetaminophen is in hundreds of products, from the over-the-counter remedies Theraflu and Excedrin to the prescription narcotics Vicodin and Percocet.