Antihistamines such as doxylamine and diphenhydramine are some sedative medications that are available over-the-counter, according to Sleepdex. Antihistamines are usually indicated for the relief of allergy symptoms.
The body tends to build up a tolerance for antihistamine medications when they are used regularly, notes Mayo Clinic. Because many over-the-counter sedatives contain antihistamines, they are best-suited for occasional use.
Doxylamine is a powerful over-the-counter sedative that sometimes causes side effects including dry mouth and nausea. Diphenhydramine was the first Food and Drug Administration-approved antihistamine drug in the United States. It may cause intense drowsiness, dizziness and difficulty urinating. Antihistamines may interact negatively with other over-the-counter and prescription drugs. A person who is taking other medications should inform her doctor before taking antihistamines as a sleep-aide, says Sleepdex.