FDA warns of serious rash risk with acetaminophen pain pills WASHINGTON (Reuters) - Tylenol and other painkillers containing the ingredient acetaminophen can cause a potentially deadly skin rash known as Stevens-Johnson Syndrome, U.S. health regulators said on Thursday. Companies that sell prescription acetaminophen will be required to add a warning about the skin rash to the drug's package insert, the Food and Drug Administration said. The agency will also request or encourage companies who sell acetaminophen products over the counter to add a warning about the risk of serious skin reactions. Reporting by Toni Clarke in Washington; Editing by Gary Hill