Glemanserin
Glemanserin is a drug which acts as a potent and selective 5-HT2A receptor antagonist. The first truly selective 5-HT2A ligand to be discovered, glemanserin resulted in the development of the widely used and even more potent and selective 5-HT2A receptor antagonist volinanserin, which is a fluorinated analogue. Though it was largely superseded in scientific research by volinanserin, glemanserin was investigated clinically for the treatment of generalized anxiety disorder and reached phase 3 trials for this use. However, it was ultimately found to be ineffective and was not marketed. The drug was also investigated for treatment of cardiac arrhythmias, but was not marketed for this use either.