Compare to Tylenol 8HR Arthritis Pain active ingredient. Acetaminophen Extended-Release Tablets, 650 mg is a pain reliever/fever reducer used for the temporary relief of minor arthritis pain. Each extended-release caplet contains 650 mg of acetaminophen and may also be used to temporarily relieve other types of pain such as: the common cold, premenstrual and menstrual cramps, headache, backache, toothache and other muscular aches.