Diphenhydramine is best described as which of the following?

Diphenhydramine is best described as which of the following?

• A. Monoamine oxidase inhibitor
• B. H2 blocker used for ulcers
• C. H1 blocker that prevents histamine response; also anticholinergic effects and CNS depression
• D. Expectorant

Answer: (C)

Diphenhydramine is best described as an H1 antihistamine that blocks histamine’s actions at the H1 receptor, which helps prevent the allergic symptoms caused by histamine such as itching and nasal/oral congestion. Because it is a first‑generation antihistamine, it easily crosses the blood-brain barrier, leading to central nervous system depression or sedation. It also has anticholinergic effects from muscarinic receptor antagonism, which can cause dry mouth, blurred vision, urinary retention, and constipation. It is not a monoamine oxidase inhibitor, nor an H2 blocker used for ulcers, nor an expectorant.

Diphenhydramine is best described as an H1 antihistamine that blocks histamine’s actions at the H1 receptor, which helps prevent the allergic symptoms caused by histamine such as itching and nasal/oral congestion. Because it is a first‑generation antihistamine, it easily crosses the blood-brain barrier, leading to central nervous system depression or sedation. It also has anticholinergic effects from muscarinic receptor antagonism, which can cause dry mouth, blurred vision, urinary retention, and constipation. It is not a monoamine oxidase inhibitor, nor an H2 blocker used for ulcers, nor an expectorant.