An anti-allergic drug having histamine H1 receptor antagonistic properties is cetirizine dihydrochloride, a hydroxyzine metabolite. Cetirizine in Zyrtec Oral Drops 10 ml temporarily reduces allergic reactions and symptoms by inhibiting the activity of histamine, a chemical that triggers the body's immune system and inflammations. It aids in the alleviation of allergy symptoms such watery eyes, congestion, itching, swelling, sneezing, and runny noses.