NPLEX II Pharmacology Practice Test

Diphenhydramine works primarily as an H1 histamine receptor antagonist, which makes it an effective antihistamine for allergy symptoms such as itching, sneezing, and runny nose. Its ability to cross into the brain also gives it sedative effects, which is why it’s used as a sleep aid in some situations. Additionally, it has anticholinergic properties that contribute to its antiemetic effects, helping prevent nausea and vomiting, particularly with motion sickness. It is not a beta-blocker, not an antipyretic, and not a diuretic, so it won’t treat fever, heart-related symptoms, or affect urine production. Hence, combining antihistamine action with sedative and antiemetic effects best fits what diphenhydramine does.