rn Please consult your physician before taking any medication. Ponstan capsules contain the active ingredient mefenamic acid, which is a type of medicine called a non-steroidal anti-inflammatory drug (NSAID). NSAIDs are used to relieve pain and inflammation. Mefenamic acid is also available without a brand name, ie as the generic medicine. Mefenamic acid works by blocking the action of a substance in the body called cyclo-oxygenase (COX). Cyclo-oxygenase is involved in the production of various chemicals in the body, some of which are known as prostaglandins. Prostaglandins are produced by the body in response to injury and certain diseases and conditions, and cause pain, swelling and inflammation. Mefenamic acid blocks the production of these prostaglandins and is therefore effective at reducing inflammation and pain.