Diclofenac. Computer molecular model of diclofenac (molecular formula: C14.H11.Cl2.N.O2), a non- steroidal anti-inflammatory drug (NSAID). It is composed of carbon (grey), hydrogen (white), oxygen (red), chlorine (green) and nitrogen (blue). Although the exact mechanism of action is not understood, it is thought that diclofenac prevents the synthesis of prostaglandin by inhibition of the enzyme cyclo-oxygenase, and this leads to the drug's anti-inflammatory, painkilling properties.