Which of the following is a common side effect of antihistamines?

Antihistamines are commonly used to alleviate symptoms associated with allergies, such as runny nose, sneezing, and itching. One of the well-known side effects of many antihistamines is drowsiness. This occurs because first-generation antihistamines, in particular, can cross the blood-brain barrier and interfere with neurotransmitters in the central nervous system, leading to sedation. This sedating effect is often why these medications are sometimes used to help with sleep issues, despite their primary function being to treat allergies.

While nausea, insomnia, and dry mouth can also be associated with antihistamine use, drowsiness stands out as a predominant and well-documented effect, making it a key consideration for both patients and healthcare providers when prescribing or taking these medications.