High doses of acetaminophen, also known as Tylenol, can damage the liver. This figure shows how acetaminophen (APAP) is broken down into a reactive compound (NAPQI) that binds covalently to proteins at cysteine residues. While this effect is well known, it does not account for all of the changes observed in acetaminophen-induced liver failure. Researchers have reported that binding by the reactive compound NAPQI activates a protein modification pathway called glutathionylation, which impairs protein function. The research illuminates early steps in a cascade of failures that can cause tissue damage, liver failure and sometimes death by acetaminophen overdose.