Nytol one a night is used to relieve temporary sleeping difficulties the active ingredient contained within nytol diphenhydramine hydrochloride is an antihistamine that causes sleepiness drowsiness sleeping difficulties can be caused due to many reasons such as jet lag stress personal problems and by taking nytol it is an aid to a good nights sleep nytol one a night has been proven to help you fall asleep faster and have a longer deeper sleep leaving you feeling fresh and rested in the