Moderately selective excitatory receptor for orexin-A and, with a lower affinity, for orexin-B neuropeptide (PubMed:9491897, PubMed:26950369). Triggers an increase in cytoplasmic Ca(2+) levels in response to orexin-A binding (PubMed:9491897, PubMed:26950369). The N-terminal region is required for orexin signaling. The antagonists suvorexant and SB-674042 bind at the cognate neuropeptide binding site that is situated between the transmembrane helices and accessible from the extracellular side of the membrane. Belongs to the G-protein coupled receptor 1 family.