The functional group in Benadryl, an antihistaminic drug, is an ethylamine group. Specifically, diphenhydramine, the active ingredient in Benadryl, contains this group. The ethylamine group is crucial for Benadryl’s pharmacological activity as it interacts with histamine receptors in the body. Benadryl is an H1 receptor antagonist, meaning it competes with histamine for binding to these receptors. By blocking histamine action, Benadryl alleviates symptoms of allergic reactions, such as itching, sneezing, and runny nose. The ethylamine group’s presence enhances the drug’s affinity for histamine receptors, making Benadryl effective in managing allergic symptoms.