The function of Ensembl gene identifier ENSG00000196639 (HRH1, histamine receptor H1) is as follows. G protein-coupled receptor for histamine, a biogenic amine that functions as an immune modulator and a neurotransmitter (PubMed:33828102, PubMed:8280179). Through the H1 receptor, histamine mediates the contraction of smooth muscles and increases capillary permeability due to contraction of terminal venules. Also mediates neurotransmission in the central nervous system and thereby regulates circadian rhythms, emotional and locomotor activities as well as cognitive functions (By similarity). {ECO:0000250|UniProtKB:P70174, ECO:0000269|PubMed:33828102, ECO:0000269|PubMed:8280179}.