Doxepin-D3 hydrochloride is a deuterium-labeled doxepin hydrochloride.Doxepin hydrochloride is an oral active tricyclic antidepressant used as a sedative.Doxepin hydrochloride is also an effective CYP450 inhibitor,significantly inhibiting CYP450 2C19 and 1A2.Doxepin hydrochloride is an effective selective histamine receptor H1 antagonist.