What do the medications Allegra, Zyrtec, and Benadryl have in common?

Allegra, Zyrtec, and Benadryl are all classified as antihistamines, which is the reason for selecting this answer. Antihistamines are commonly used to relieve symptoms of allergies, such as sneezing, runny nose, and itchy or watery eyes. They work by blocking the action of histamine, a substance in the body that triggers allergic symptoms. Each of these medications is effective in treating allergic reactions and associated symptoms, making this category their shared characteristic.

In contrast, the other options do not apply. Antibiotics are used to treat bacterial infections, which is not the function of these medications. They do not treat anxiety disorders, as anxiety requires different types of medications, typically anxiety relievers or antidepressants. Lastly, while some antihistamines may help with sleep due to their sedative effects, they are not intended for pain management, which typically involves a different class of drugs such as analgesics. This context highlights why the correct choice is specific to their classification as antihistamines.