Overview Diphenhydramine is a first-generation antihistamine commonly used to treat allergies, insomnia, and motion sickness. It is widely available over the counter (OTC) and is found in various formulations, including tablets, capsules, liquids, and topical creams. While effective, it can cause drowsiness and other side effects, making it important to use it properly. What is Diphenhydramine? Diphenhydramine is an antihistamine that works by blocking histamine, a chemical responsible for allergic reactions. It also has sedative properties, which make it useful for sleep aid and motion sickness prevention. How It Works Diphenhydramine blocks histamine H1 receptors, preventing allergy symptoms like itching,…