Buy Fioricet 40mg online this medication is used to treat tension headaches and other types of primary headaches. Acetaminophen is a pain reliever and fever reducer. Caffeine helps increase the effects of acetaminophen. Butalbital (acetaminophen/caffeine/butalbital) belongs to a class of drugs known as barbiturates. It works by slowing down nerve impulses in the brain that trigger migraine and cluster headache pain.