Diphenhydramine is an antihistamine active ingredient that has a number of different uses in over-the-counter (OTC) medicines. Depending on the dose and form, the active ingredient diphenhydramine can be used to treat hay fever and other allergies, help reduce occasional sleeplessness, or relieve skin irritations and itching. It may be written as diphenhydramine, diphenhydramine hydrochloride (HCl), or diphenhydramine citrate, but each has the same effect in the human body.
When taken orally, diphenhydramine can be the only active ingredient in allergy medicines, or it can be combined with other ingredients in multi-symptom cough and cold products. In a higher strength, diphenhydramine is available in single-ingredient oral nighttime sleep-aid medicines, as well as in combination products that relieve other symptoms, such as aches and pains. When used externally, diphenhydramine may be combined with other active ingredients in topical pain medicines (i.e., those applied to the body’s surface).
Diphenhydramine is approved by the U.S. Food and Drug Administration (FDA) and is safe and effective when used according to the Drug Facts label. Taking too much of any medicine could potentially cause a problem. In order to avoid taking too much diphenhydramine, do not use an oral diphenhydramine-containing medicine at the same time as a topical product that also contains diphenhydramine.