Follow your doctor's advice. Take Zyrtec exactly as prescribed. The normal suggested dose for adults is one 10 mg tablet daily. If you miss a dose of Zyrtec, take it as soon as you remember. If it's almost time for your next scheduled dose, skip it and continue with your regular dosing schedule.

In clinical studies, less than 3 percent of patients quit taking Zyrtec because of side effects. The most common side effects reported in clinical trials were drowsiness, fatigue, and dry mouth.

If you experience an allergic reaction during your treatment, stop taking Zyrtec and seek medical attention immediately. Symptoms of an allergic reaction include rash, itching, swelling, dizziness, and/or trouble breathing.