Almorexant hydrochloride (ACT-078573 hydrochloride) is a potent and competitive dual orexin 1 receptor (OX1)/orexin 2 receptor (OX2) antagonist with Ki values of 1.3 and 0.17 nM for OX1 and OX2, respectively.

Almorexant inhibits the increase in intracellular Ca2+ induced by 10 nM human orexin-A in Chinese hamster ovary cells with IC50 of 16 nM (rat) and 13 nM (human) for the OX1 receptor and 15 nM (rat) and 8 nM (human) for the OX2 receptor. [1]

Almorexant (300 mg/kg p.o.) decreases alertness, and increases electrophysiological indices of both non-REM and REM sleep in male Wistar rats. In dogs, Almorexant (100 mg/kg p.o.) causes somnolence and increases surrogate markers of REM sleep. [1] Almorexant induces a robust antidepressant-like effect and the restoration of stress-related HPA axis defect independently from a neurogenic action. [2] In addition, Almorexant also reduces ethanol self-administration in high-drinking rodent models. [3]