Diphenhydramine hydrochloride is an antihistamine commonly used to relieve symptoms of allergies, hay fever, and the common cold. It works by blocking the action of histamine, a substance in the body that causes allergic symptoms. This medication can help reduce sneezing, runny nose, and itching. Additionally, Diphenhydramine is often used as a short-term treatment for insomnia due to its sedative properties. It is available in various forms, including tablets, capsules, and liquid. As with any medication, it is important to follow dosage instructions and consult a healthcare professional if you have any concerns.