My patients frequently ask me which over-the-counter antihistamine they should take -- Claritin, Zyrtec or Allegra? You might be thinking, "Wait a second, I didn't know Allegra is available over-the-counter?" As of now, it isn't, but Allegra should be available over-the-counter this spring. But, if you're thinking these antihistamines are all the same -- well, they aren't. Depending on the allergic condition being treated, the age of the person, as well as other underlying issues (such as pregnancy), the best choice of antihistamine might be different. So, instead of thinking that these medicines are all the same, learn more about each one of them and figure out which choice is the best for you.