Which of the following is an example of an antihistamine?

Benadryl is an example of an antihistamine because it contains diphenhydramine, which is a first-generation antihistamine effective in blocking the action of histamine at H1 receptors. This helps alleviate symptoms associated with allergies, such as sneezing, runny nose, and itching. Antihistamines work by preventing histamine from attaching to its receptors, thus reducing allergy symptoms.

In contrast, the other options serve different purposes: Advil is a nonsteroidal anti-inflammatory drug (NSAID) used primarily for pain relief and reducing inflammation; Zithromax is an antibiotic used to treat bacterial infections; and Lipitor is a medication prescribed to lower cholesterol levels. Each of these medications operates through different mechanisms and is used for different medical conditions, highlighting the specific role of antihistamines like Benadryl in allergy management.