Diphenhydramine is more likely to cause which effect compared with second-generation antihistamines?

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Multiple Choice

Diphenhydramine is more likely to cause which effect compared with second-generation antihistamines?

Explanation:
Sedation is the key difference. Diphenhydramine is a first‑generation H1 blocker that readily crosses the blood–brain barrier, so it strongly blocks central histamine receptors and causes drowsiness. Second‑generation antihistamines are designed to limit CNS entry (lower lipophilicity and active efflux by P‑glycoprotein), so they produce much less sleepiness. The other options aren’t characteristic effects that differentiate these drug classes, while drowsiness is the hallmark side effect that makes diphenhydramine more sedating.

Sedation is the key difference. Diphenhydramine is a first‑generation H1 blocker that readily crosses the blood–brain barrier, so it strongly blocks central histamine receptors and causes drowsiness. Second‑generation antihistamines are designed to limit CNS entry (lower lipophilicity and active efflux by P‑glycoprotein), so they produce much less sleepiness. The other options aren’t characteristic effects that differentiate these drug classes, while drowsiness is the hallmark side effect that makes diphenhydramine more sedating.

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