The antihistamine Benadryl has a sedative effect, but the antihistamine Zyrtec does not, because
A) Benadryl is taken as a liquid and Zyrtec as a pill.
B) Benadryl costs more than Zyrtec.
C) Zyrtec crosses the blood-brain barrier but Benadryl does not.
D) Benadryl crosses the blood-brain barrier but Zyrtec does not.

Question

Quizplus · Accepted Answer

The sedative effect of Benadryl is due to its ability to cross the blood-brain barrier and bind to histamine receptors in the brain, leading to drowsiness. Zyrtec, on the other hand, does not easily cross the blood-brain barrier, and therefore does not cause sedation. The other options provided in the question (A and B) are not relevant to the reason for the difference in sedative effect between these two antihistamines.

The Antihistamine Benadryl Has a Sedative Effect, but the Antihistamine