Zyrtec is an antihistamine medication containing 10mg of Cetirizine dihydrochloride per tablet. It comes in a pack of 20 film-coated tablets and is used to treat allergy symptoms like sneezing, runny nose, watery eyes, and itching from hay fever and other allergies. Zyrtec provides 24-hour relief from allergy symptoms. The active ingredient Cetirizine dihydrochloride works by blocking histamine, a substance that causes allergic symptoms. The tablets are film-coated for easy swallowing. This is a prescription medication that should be taken as directed by your healthcare provider. Common side effects may include drowsiness, dry mouth, and fatigue.