Nytol One-A-Night is a clinically proven sleep aid that helps you drift off, sleep soundly and wake up refreshed after a full nights sleep. Used to relieve temporary sleeplessness.  And let’s get a little sciencey for a second. Nytol One-A-Night contains a commonly used antihistamine called diphenhydramine hydrochloride (trust us it’s easier to use than to say!) It works by blocking the normal actions of histamine, the chemical that stimulates arousal-promoting areas of the brain. This helps reduce alertness and promote that first drowsy stage of sleep, helping you to then drift off into a restful, deeper sleep.