Nytol How does it work? Diphenhydramine belongs to a group of medicines called sedating antihistamines. Diphenhydramine enters the brain in significant quantities and causes marked drowsiness. It decreases the time taken to fall asleep and increases the depth and quality of sleep. Therefore, diphenhydramine is commonly used for temporary relief of sleep disturbances. Histamine is a chemical produced by the body that stimulates the symptoms of an allergic reaction such as inflammation of the skin, airways or tissues, rashes, itching of the skin, eyes or nose, nasal congestion or narrowing of the airways. As diphenhydramine is an antihistamine it blocks the action and therefore effects, of histamine. This results in the prevention or relief of the typical symptoms of an allergic reaction. Diphenhydramine is used for this purpose in many cold and flu preparations. What is it used for? Temporary relief of sleep disturbances Warning! This medicine may cause drowsiness. If affected do not drive or operate machinery. Alcohol should be avoided. The effectiveness of this medicine may decrease if used for long periods of time (tolerance). Use with caution in Abnormal muscle weakness Seizure disorders, eg due to brain injury or epilepsy Not to be used in Asthma Blockage of the area where the stomach joins the intestines (pyloro-duodenal obstruction) Blockage of the drainage passage of the bladder (bladder neck obstruction) Children under 16 years of age Closed angle glaucoma Enlarged prostate gland Peptic ulcer causing narrowing of an area of the gut passage This medicine should not be used if you are allergic to one or any of its ingredients. Please inform your doctor or pharmacist if you have previously experienced such an allergy. If you feel you have experienced an allergic reaction, stop using this medicine and inform your doctor or pharmacist immediately.