Acetaminophen by itself doesn't have caffeine in it. But when you take an acetaminophen or aspirin tablet, you're not taking pure drug, or else it would kill you. You're taking the drug plus chemicals that help the drug absorb, make it stay in the body longer, etc. One of these ingredients is caffeine. A big reason they put caffeine in pain reliever medicine is because it can give you a little pep to make you feel better. Another reason is because a lot of people who take them for headaches are suffering from caffeine withdrawal. Drink 2 cups of coffee a day for a month and then stop for a few days and see how it feels. The small amount of caffeine in the pill will make these headaches go away.