Which of the following is an antihistamine?

Claritin, also known as loratadine, is classified as an antihistamine because it specifically works by blocking the action of histamine, a substance in the body that causes allergic symptoms. Antihistamines are commonly used to alleviate symptoms associated with allergies such as runny nose, sneezing, and itching.

In contrast, Proventil HFA is a bronchodilator used primarily for asthma, Zestril is an antihypertensive medication (an ACE inhibitor) used to treat high blood pressure, and Lopressor is a beta-blocker used to manage hypertension and heart conditions. Each of these medications serves entirely different therapeutic purposes, confirming Claritin as the only option that fits the antihistamine classification.