Diphenhydramine

Diphenhydramine (CAS No.: 58-73-1) is a first-generation histamine H1 receptor antagonist widely employed as a pharmacological tool in neuropharmacology and immunology research, characterized by prominent anticholinergic activity and central nervous system penetration due to its ability to cross the blood–brain barrier. Mechanistically, it acts primarily through competitive inhibition of H1 receptors, thereby modulating histamine-mediated signaling pathways, while also interacting with muscarinic acetylcholine receptors and exhibiting off-target effects such as inhibition of NMDA receptor-mediated currents at low micromolar concentrations. These combined activities make it a useful compound for investigating the interplay between histaminergic, cholinergic, and glutamatergic systems in cellular and animal models. In vitro studies demonstrate that diphenhydramine can modulate receptor activity and ion channel function in the low micromolar range, supporting its application in receptor binding assays and electrophysiological analyses. Additionally, it is frequently utilized in experimental paradigms examining neurobehavioral responses, blood–brain barrier permeability, and mechanisms of central sedation and sensory processing. The concentrations or doses used in experiments typically depend on specific experimental designs and research objectives, making diphenhydramine a versatile reference compound in studies of receptor pharmacology and central nervous system function.