Diphenhydramine: A Review of Its Clinical Applications and Potential Adverse Effect Profile

Diphenhydramine (Benadryl) is a first-generation antihistamine that is primarily used to treat allergic reactions including anaphylaxis, urticaria, and allergic rhinitis. Despite its availability as an over-the-counter medication, adverse physiologic effects and toxicity may occur with its use especially when administered rapidly via the intravenous route or when administered in large or excessive doses. The development and history of diphenhydramine is presented, its physiologic effects and clinical uses outlined, previous reports of clinically significant and potentially life-threatening adverse effects reviewed, and options to limit these effects discussed.