Doxylamine succinate is an antihistamine for allergy symptoms such as cough, sneezing and watery eyes. Manufacturers also sell the drug for relief of insomnia. It is sold under the brand name Unisom, according to WebMD.
Patients using doxylamine succinate should follow the label directions exactly and not increase or reduce the dosage from the printed instructions unless directed by their doctor. Drugs.com recommends only using this medication for insomnia when able to dedicate several hours to sleep. It is not for treating insomnia in children without a doctor's direction. Individuals using the medication for allergies should call a doctor if the condition fails to improve within a week. For insomnia, the individual should call a doctor if he does not get relief within two weeks.