First, Zyrtec may work faster than Claritin. Studies show that cetirizine, the active ingredient in Zyrtec, can start working in as little as 20 minutes while loratadine, Claritin's active ingredient, ...

While Allegra, Claritin, and Zyrtec are all in the same family of drugs — antihistamines — they each have different active ingredients, and there are some differences between them. The same ...