Doxepin hydrochloride (Standard) is the standard substance of Doxepin hydrochloride, and it is applicable for quantitative analysis, quality control, and related research in biochemical experiments. Doxepin hydrochloride (Aponal) is a dibenzoxepin tricyclic compound. It displays a range of pharmacological actions including maintaining adrenergic innervation. Its mechanism of action is not fully understood, but it appears to block reuptake of monoaminergic neurotransmitters into presynaptic terminals. It also possesses anticholinergic activity and modulates antagonism of histamine H(1)- and H(2)-receptors.