if you can buy a drug sitting next to the toothpaste and shampoo, how dangerous could it be? so, before you grab a bottle of pain reliever the next time you have a headache, learn some dos and don'ts first. the same chemicals that amplify pain -- which some pain medicines block -- also help maintain the protective lining of the stomach and intestines. acetaminophen -- the active ingredient in tylenol -- works differently and poses a much lower risk of gi problems. cryer admits that balancing the benefits and risks of these medicines can be tricky.