Which of the following medications can cause drowsiness as a side effect?

Antihistamines are known for their sedative properties, which often lead to drowsiness as a common side effect. This occurs because many antihistamines can cross the blood-brain barrier and interfere with the central nervous system, which can produce a calming effect. Understanding this characteristic is crucial for healthcare providers when advising patients about the potential side effects, especially when activities requiring alertness, such as driving, are involved.

In contrast, cathartics primarily affect bowel movements and are not associated with drowsiness. Decongestants primarily target nasal congestion and can sometimes lead to increased alertness due to their stimulant effects. Antitussives, generally used to relieve cough, may have some formulations that can cause drowsiness; however, not all do, and they are not as consistently sedating as antihistamines. Therefore, antihistamines are the most recognized class of medications associated with causing drowsiness among the options provided.