Cipralisant is an extremely potent Histamine H₃ receptor ligand originally developed by Gliatech. Cipralisant was initially classified as a selective H₃ antagonist, and seemed to be well tolerated during early testing, entering Phase II trials for ADHD in 2000.

The relatively recent cloning of human H₃ receptor, as well as the discovery of its constitutive activity provided the ability to better assess the activity of H₃ receptor ligands. Consequently cipralisant was reassessed as an H₃ receptor agonist in human and rat recombinant systems, showing functional selectivity

Functional Selectivity

Functional selectivity is the ligand-dependent selectivity for certain signal transduction pathways in one and the same receptor. This can be present when a receptor has several possible signal transduction pathways...

 and stimulating one type of G-protein coupled pathway while failing to activate other intracellular pathways.

Gliatech filed for bankruptcy in 2002, and its intellectual property was inherited by Merck

Merck & Co.

Merck & Co., Inc. , also known as Merck Sharp & Dohme or MSD outside the United States and Canada, is one of the largest pharmaceutical companies in the world. The Merck headquarters is located in Whitehouse Station, New Jersey, an unincorporated area in Readington Township...

. The development of cipralisant seems to have been suspended since 2003 but research is ongoing, and recently it has been shown that it is the 1S,2S enantiomer which is the biologically active one.