At these low doses, doxepin mainly blocks histamine (it is a selective H1 blocker, or histamine H1 receptor antagonist), with very little antidepressant effect and few drying side effects such as dry mouth or constipation. Sold under the brand name Silenor, it is approved for adults who have trouble staying asleep (sleep maintenance insomnia). Unlike the higher doses of doxepin used for depression and anxiety, low-dose doxepin mainly works as a sleep aid, without much effect on norepinephrine or serotonin.