I suppose you mean cetirizine, an antihistamine.
Information at MedHelp:
If overdose is suspected, contact your local poison control center or emergency room immediately. US residents can call the US National Poison Hotline at 1-800-222-1222. Canada residents can call a provincial poison control center. Symptoms of overdose may include: severe drowsiness. In children, symptoms may include: restlessness and irritability, and may be followed by drowsiness.
Information at www.drugs.com:
Seek emergency medical attention if you think you have used too much of this medicine.
Overdose symptoms may include feeling restless or nervous, and then feeling drowsy.