Many generic sleep aids consist solely of one active ingredient – diphenhydramine.It is one of the oldest antihistamines available (classified as a first-generation antihistamine), but for many patients surpasses the efficacy of even new prescription drugs.It then produces histamine, which causes symptoms such as rashes, a runny nose and/or sneezing.Antihistamines help stop this happening if you take them before you come into contact with the substance you're allergic to. They're also sometimes used to prevent motion sickness and as a short-term treatment for sleeping difficulties (insomnia).Most antihistamines can be bought from pharmacies and shops, but some are only available on prescription.
Diphenhydramine was the first antihistamine approved by the FDA (in the 1940s) and is widely used in OTC sleeping pills.
Non-drowsy antihistamines are generally the best option, as they're less likely to make you feel sleepy.
But types that make you feel sleepy may be better if your symptoms affect your sleep.
Food and other drinks don't affect most antihistamines, but check the leaflet that comes with your medicine to make sure.
Some antihistamines may not be suitable in these cases.