Doxepin (oral capsules)

Doxepin is a tricyclic antidepressant that also occupies histamine H1 and H2 receptors. That antihistamine action occurs downstream of mast-cell degranulation: it prevents released histamine from signalling at its receptors rather than removing the trigger for release.

A separate laboratory paper exposed isolated rat peritoneal mast cells to several tricyclic antidepressants, including doxepin, and measured serotonin secretion, uptake, and reuptake. That is why this entry records non-human laboratory work on mast cells. It does not show that the oral capsule directly stabilizes human mast cells at clinical exposure.

The randomized human evidence is a double-blind placebo-controlled crossover study in 16 adults with chronic idiopathic urticaria. The investigators measured lesion and itch scores, additional antihistamine use, and histamine- and codeine-induced skin wheals. Chronic urticaria is not MCAS, and suppression of a wheal does not identify whether receptor antagonism or a mast-cell effect produced the measurement.

The AAAAI work-group report includes doxepin in its MCAS management table, but that source is clinical guidance rather than a doxepin outcome study. This page is limited to the oral-capsule evidence object used in the urticaria literature and current major-depression label; topical cream and insomnia-specific tablet formulations have different labels and exposure.