Fexofenadine, loratadine, cetirizine, and diphenhydramine are the four most popular medications used to treat allergies. These medications are antihistamines, which help to block the action of histamine, a chemical released in the body which causes an allergic reaction. Although these medications are all antihistamines, there are some differences between them. Fexofenadine (most commonly sold as “Allegra”) and loratadine (most commonly sold as “Claritin”) are both long-acting medications, meaning that they can last up to 24 ...