It is expressed in smooth muscles, on vascular endothelial cells, in the heart, and in the central nervous system.

The H1 receptor is linked to an intracellular G-protein (Gq) that activates phospholipase C and the inositol triphosphate (IP3) signalling pathway.

[7] H1-antihistamines have been shown to attenuate NF-κB expression and mitigate certain inflammatory processes in associated cells.

[10] H1-antihistamines that cross the blood–brain barrier inhibit H1 receptor activity on neurons that project from the tuberomammillary nucleus.

Antihistamine drugs effectively prevent viral infection by competitively binding to HRH1, thereby disrupting the interaction between the spike protein and its receptor.