Common side effects include sleepiness, dry mouth, constipation, nausea, and blurry vision. Serious side effects may include increased risk of suicide in those under the age of 25, mania, and urinary retention. A withdrawal syndrome may occur if the dose is rapidly decreased. Use during pregnancy and breastfeeding is not generally recommended. Doxepin is a tricyclic antidepressant (TCA). While how it works for treating depression remains an area of active inquiry, it may involve increasing the levels of norepinephrine, along with blocking histamine, acetylcholine, and serotonin.