Mefenamic acid drug molecule. Computer model of a molecule of the anti-inflammatory drug mefenamic acid (marketed as Ponstel). Atoms are represented as rods and are colour-coded: carbon (pink), hydrogen (white), oxygen (blue) and nitrogen (yellow). Mefenamic acid is a non-steroidal anti- inflammatory drug (NSAID). It is taken as an analgesic (painkiller) and an antipyretic (fever reducing drug) as well as an anti-inflammatory drug. It is thought to work by inhibiting the enzyme cyclo-oxygenase, which synthesises prostaglandin, the molecule transmits pain signals to the brain. Mefenamic acid is used to treat rheumatoid arthritis and pain caused by heavy periods.