Acetaminophen is the active ingredient in TYLENOL. TYLENOL products do not contain aspirin, ibuprofen, or naproxen, the active ingredients found in other common nonprescription pain relievers. Each of these active ingredients relieves pain, but they work differently. While the mechanism of action of TYLENOL is not fully understood, it is thought that TYLENOL works by elevating the body’s overall pain threshold so you feel less pain and lowers your fever by helping your body eliminate excess heat. Learn more about active ingredients by comparing pain relievers here.