Adipiplon (developmental code name NG2-73) is an anxiolytic drug developed by Neurogen Corporation. It has similar effects to benzodiazepine drugs, but is structurally distinct and classed as a nonbenzodiazepine anxiolytic. Adipiplon is a subtype-selective GABAA receptor partial agonist, which binds preferentially to the α3 subtype. This is significant as while several previous nonbenzodiazepine drugs have been developed that are selective for α2/3 over the other subtypes, adipiplon is one of the first drugs selected for clinical development which can discriminate between α2 and α3, as well as showing a little affinity for the α1 or α5 subtypes — alpidem is selective for α3 over α2, but still has moderate affinity for α1, whereas adipiplon is highly α3-selective with little affinity for either α1, α2 or α5. Adipiplon was being researched as a potential medication for the treatment of anxiety and insomnia, and in 2008 it was being used in Phase IIb trials. These trials were suspended after significant next-day side effects were discovered.