Cetirizine hydrochloride, brand name Zyrtec, reduces the amount of histamine in the body, according to Drugs.com. Elevated histamine levels cause sneezing, a runny nose, itching and watery eyes. Cetirizine hydrochloride helps treat colds and allergies with these symptoms.
Cetirizine hydrochloride is approved for use in adults and in children 6 months and older, says Drugs.com. Drowsiness, dizziness, fatigue and dry mouth are common side effects, states RxList.com. Children may also experience stomach pain and vomiting. Alcohol, anti-anxiety medications and other central nervous system depressants should be avoided while using the medication as they can exacerbate the drowsiness caused by the medication.