Jan 14, Zyrtec contains cetirizine and Claritin contains loratadine. dry mouth · constipation or diarrhea; abdominal cramps and pain; eye redness. Oct 15, Learn about the potential side effects of Claritin (loratadine). wheezing, fatigue, hyperkinesia, abdominal pain, conjunctivitis, dysphonia. Zyrtec and Claritin are similar over-the-counter medicines that can help to reduce your allergy symptoms. Your choice may come down to a subtle difference.