: The active ingredient in Benadryl , ZzzQuil , and Sominex . It is a first-generation antihistamine that causes significant sleepiness within about an hour.

: Found in Unisom SleepTabs and NyQuil. This antihistamine tends to stay in the system longer than diphenhydramine, which may lead to a "hangover" feeling the next morning. Natural and Herbal Sedatives

These medications are regulated by the FDA and are often used as "nighttime sleep aids" because their primary side effect is drowsiness.