<p>Doxepin hydrochloride is one of a class of agents known as dibenzoxepin tricyclic antidepressant compounds. Although doxepin HCl does have H1 and H2 histamine receptor blocking actions, the exact mechanism by which doxepin exerts its antipruritic effect is unknown. It can produce drowsiness in significant numbers of patients, and this sedation may reduce awareness, including awareness of pruritic symptoms.</p>