H1 antihistamine

Doxepin is a tricyclic antidepressant first approved in the United States in 1969 that is now also licensed there, at 3 and 6 mg, for insomnia marked by trouble staying asleep: doses 10 to 100 times lower than antidepressant ones. At those doses it acts almost only as a histamine H1 blocker. In industry-funded trials of up to 12 weeks it cut time awake during the night by about 22–23 minutes, with little effect on how quickly people fell asleep, and the American Academy of Sleep Medicine gives it a weak recommendation for sleep maintenance on evidence it rates as very low quality. At 75–300 mg a day it is a sedating antidepressant with the anticholinergic side effects and overdose toxicity of its class.