GW 274150 was developed by GlaxoSmithKline as a selective inhibitor of inducible nitric oxide synthase (iNOS; also known as NOS2). Nitric oxide synthase (NOS) is an important chemical involved in the production of NO. Reduction of NOS, and therefore NO, may be an effective technique for the treatment of migraine headache. GW 274150 offered the potential of anti-inflammatory activity in migraine through a novel mechanism of action. The drug has completed phase II of the clinical trials for patients with rheumatoid arthritis and migraine disorders. In addition, GW 274150 was involved in phase I clinical trial for patients with mild asthma. However, all these studied were discontinued.