Even so, newer antihistamines like Allegra and Zyrtec are known to cause side effects like: Nausea Diarrhea Headache Back pain Lethargy According to a landmark 2010 study published in the journal ...

Anti-histamines combined with a decongestant are usually marked with a "D." Claritin-D, Allegra-D, and Zyrtec-D all contain a decongestant called pseudoephedrine, the same active ingredient that ...

There are a couple of ways to deal with seasonal allergies. Oral antihistamines such as Zyrtec, Allegra and Claritin help curb sinus issues. Corticosteroid nasal sprays such as Flonase ...