Cyamemazine is a neuroleptic agent that contains the phenothiazine chromophore. Cyamemazine is often used as an anxiolytic. Cyamemazine is a potent 5-HT3 (Ki of 12 nM), 5-HT2A (Ki = 1.5 nM) and 5-HT2C (Ki of 75 nM) receptors antagonist with antipsychotic activity[1][2].

Cyamemazine exhibits a high affinity for dopamine receptors, which is consistent with its antipsychotic activity. The antagonist activity of Cyamemazine at muscarinic receptors is consistent with its affinity for M1 (Ki = 13 nM), M2 (Ki = 42 nM), M3 (Ki = 321 nM), M4 (Ki = 12 nM), and M5 (Ki = 35 nM) receptors[1].

Cyamemazine behaves as an antagonist at the 5-HT3, 5-HT2C, and 5-HT2A receptors in 5-HT3-dependent contraction of isolated guinea pig ileum and bradycardic responses in rats, in 5-HT2C-dependent phospholipase C stimulation in the rat brain membrane, and in 5-HT2A-dependent contraction of isolated rat aorta rings and isolated guinea pig trachea. Cyamemazine antagonizes 5-HT3 and 5-HT2C receptors and that this effect is partially involved in its therapeutic activity in anxiety disorders. Acute administration of low doses of Cyamemazine can reduces extracellular dopamine and metabolite concentrations in rat striatum[1].

[1]. Bourin M, et al. Preclinical and clinical pharmacology of cyamemazine: anxiolytic effects and prevention of alcohol and benzodiazepine withdrawal syndrome. CNS Drug Rev. 2004 Fall;10(3):219-29. [2]. Vendrell-Criado V, et al. Photobehavior of the antipsychotic drug cyamemazine in a supramolecular gel protective environment. J Photochem Photobiol B. 2020 Jan;202:111686.