You cannot take acetaminophen and Alka-seltzer together. This is because they perform similar tasks in the body whereby, acetaminophen is a pain reliever for minor aches mostly used for headaches. Read more from http://en.wikipedia.org/wiki/Paracetamol. Alka-seltzer on the other hand is a multipurpose pain reliever which also caters for heartburn. Read more from http://en.wikipedia.org/wiki/Alka-Seltzer.