Tetrahydrozoline-d4 (hydrochloride) is the deuterium labeled Tetrahydrozoline hydrochloride. Tetrahydrozoline hydrochloride (Tetryzoline hydrochloride), a derivative of imidazoline, is an α-adrenergic agonist that causes vasoconstriction. Tetrahydrozoline hydrochloride is widely used for the research of nasal congestion and conjunctival congestion[1][2].