Diphenhydramine hydrochloride (HCL) is a sedating antihistamine that is used to counter temporary sleep disturbance in adults. As an antihistamine, diphenhydramine hydrochloride blocks the effects of the compound histamine within the body. The chemical name for diphenhydramine hydrochloride is 2-(Diphenylmethoxy)-N,N-dimethylethylamine hydrochloride.As well as being a sedative, diphenhydramine hydrochloride also has anticholinergic and antiemetic qualities. Anticholinergic means that it blocks the neurotransmitter acetylcholine and its antiemetic properties means that it alleviates nausea and vomiting, which is why it is also used to treat motion sickness.Diphenhydramine hydrochloride is used is some products to help provide relief for those suffering from pain at night-time that is preventing them from getting to sleep. This can include rheumatic or muscle pain, neuralgia, backache, toothache, migraine, headache, and period pain.Diphenhydramine hydrochloride is effective within 15 to 30 minutes of being taken orally. Its effects will last approximately 4 to 8 hours. Almost all of the diphenhydramine hydrochloride, about 95%, is metabolised by the liver.