Adipiplon is an oral, partial agonist of the GABAA alpha-3 (α3) receptor that was being developed by Neurogen Corporation for the treatment of insomnia, anxiety disorders and schizophrenia. Adipiplon has been tested in Phase 1 and 2 studies in over 600 subjects for the treatment of insomnia, demonstrating statistical significance compared to placebo on primary endpoints for sleep initiation and maintenance in patients with chronic insomnia. Adipiplon has also demonstrated statistical significance compared to placebo for self-reported quality of sleep in all completed Phase 2 studies to date. Additionally, in studies completed to date it has been well tolerated at all doses tested. Development of adipiplon was discontinued during 2008.