There are currently only a handful of what are considered second-generation antihistamines. These are drugs that can prevent allergy symptoms while NOT causing the drowsiness that most of the first-generation antihistamines brought on.

The original second-generation drugs included Claritin, Allegra, and Zyrtec. Though all are similar in action and scope, each one has been approved for slightly different uses by the FDA. A couple of years ago, Claritin's patent expired and it went both generic...