Doxepin is a tricyclic dibenzoxepin compound, primarily utilized as an active pharmaceutical ingredient (API) in the formulation of antidepressants for treating depression and anxiety disorders. It functions by modulating neurotransmitter levels in the brain, such as serotonin and norepinephrine, to improve mood and alleviate symptoms of sadness or worry.

In lower concentrations, it serves as a component in medications for managing insomnia, especially sleep maintenance issues. Doxepin is also incorporated into topical formulations for chronic pruritic skin conditions like eczema and dermatitis, where it reduces itching and inflammation through antihistaminic and sedative effects.

As a chemical reagent, doxepin is supplied as a light yellow liquid with purity greater than 98%, confirmed by infrared spectroscopy and NMR to conform to structure. It is used in pharmaceutical research, synthesis, and quality control applications.