Doxepin is used to treat depression and anxiety. Doxepin is in a class of medications called tricyclic antidepressants. It works by increasing the amounts of certain natural substances in the brain that are needed for mental balance. Doxepin is also available as a tablet to treat insomnia. This monograph only gives information about doxepin for depression or anxiety. If you are using this medication for insomnia, read the monograph entitled doxepin (insomnia).