Alka-Seltzer original effervescent tablets contain three active ingredients, aspirin, sodium hydrogen carbonate and citric acid.
Aspirin belongs to a group of medicines called non-steroidal anti-inflammatory drugs (NSAIDs). It works by blocking the action of an enzyme in the body called cyclo-oxygenase (COX).
COX is involved in making substances in the body known as prostaglandins, in response to injury and in certain conditions. The prostaglandins cause pain, swelling and inflammation. Aspirin reduces inflammation and pain by reducing the production of these prostaglandins.