How Does Nytol One A Night Work?The active ingredient in Nytol is Diphenhydramine.Diphenhydramine helps to block the normal actions of the chemical histamine. Histamine stimulates the arousal-promoting areas of the brain, Nytol helps to help reduce alertness and help promote drowsiness, leading you into the first stage of sleep which makes it a lot easier to fall into a deep, restful sleep.How To Take Nytol One A Night TabletsAdults; Take one tablet 20 minutes before bedtime.Nytol is not suitable for children under 16 years of age.Do not take this product if you are asthmatic, are pregnant, have a peptic ulcer or have narrow-angle glaucoma.Avoid alcohol.Avoid driving and operating machinery if affected by drowsiness.If this medicine is taken for a prolonged period, you may become tolerant to the effects and it will become less effective at promoting sleep.Consult your doctor if you continue to have trouble sleeping.