The active ingredient in Benadryl™ is the drug diphenhydramine hydrochloride, sometimes simply called diphenhydramine or by one of two abbreviations, DPH and DPM. Diphenhydramine was one of the first antihistamines available and was developed in the 1940s. It was the first drug approved as a prescription antihistamine, blocking the effects on the body of a naturally occurring chemical called histamine, which the human body produces as a response to allergens. Today, it is commonly available over the counter in a very large number of products of which Benadryl™ is one of the more well known brands. Its primary use is for the treatment of symptoms of common allergies, such as hay fever, but it is also used as an ingredient in sleep aid medications, due to its sedative effect, to treat hives and skin rashes due to allergic reactions, and for other uses.
While many of the products sold under the Benadryl™ brand contain other active ingredients, such as acetaminophen and phenylephrine, the only active ingredient in Benadryl™ itself is diphenhydramine. Benadryl™ is sold as a treatment for symptoms of the common cold or allergies such as hay fever or pet allergies. Formulations containing the active ingredient in Benadryl™ are sold as both an ingestible medication and as a topical ointment or cream. The topical forms are used locally to treat mild pain, swelling and itching of skin rashes, hives and insect bites.
Diphenhydramine is not the active ingredient in Benadryl™ only. It is present in a large number of products, sold by many manufacturers, and is often combined with other medications for the treatment of cold and flu symptoms. The drug is used for a number of purposes besides the treatment of allergy symptoms. Motion sickness, the symptoms of Parkinson's disease and severe allergic reactions can all be treated with diphenhydramine.
As diphenhydramine can have several possible effects on the human body other than as an antihistamine, it is sometimes used for other uses than described on the package, sometimes at the suggestion of a doctor or pharmacist. Of course, no medication should be used in any way other than indicated by its instructions without first consulting a doctor. Failure to use any medication in accordance with its instructions or those of a doctor can result in serious health problems.