Zyrtec Allergy Liquid Gels provide 24 Hour relief of your worst indoor and outdoor allergy symptoms. With 10 milligrams of cetirizine hydrochloride per capsule, this prescription-strength allergy medicine provides 24 hours of relief from common symptoms of hay fever and other upper respiratory allergies: runny nose, sneezing, itchy and watery eyes, and itching of the nose or throat. Zyrtec is the number-one allergist-recommended brand among OTC oral antihistamines. It is effective in treating indoor allergies from dust, mold, and pet dander, and outdoor, seasonal allergies from tree pollen, weeds, and grasses. Zyrtec is indicated for use by adults and children six years and older; one dose starts working at hour 1 and keeps on working for a full 24 hours.