Diphenhydramine is a first-generation antihistamine that works by blocking H1 histamine receptors, helping to relieve allergy symptoms, hay fever, common cold effects, and motion sickness, such as sneezing, itching, runny nose, and watery eyes. It also has sedative and anticholinergic properties, which make it useful in sleep aids and for preventing nausea. First synthesized in 1943 by American chemist George Rieveschl during research on antihistamines, diphenhydramine was introduced commercially in the late 1940s and 1950s. It quickly became widely used not only for allergic reactions but also for its calming and antiemetic effects. Over time, it has been incorporated into numerous over-the-counter and prescription products worldwide, establishing itself as a versatile and essential drug in both clinical and self-care settings.
