What is doxepin (Sinequan) (Sinequan)? Doxepin is a tricyclic antidepressants. Doxepin affects chemicals in the brain that may become unbalanced. Doxepin (Sinequan or other generic name) is used to treat symptoms of depression and/or anxiety associated with alcoholism, psychiatric conditions, or manic-depressive conditions. Doxepin may also be used for purposes not listed in this medication guide.