Do NOT use Zyrtec if:

You are allergic to any ingredient in Zyrtec or to hydroxyzine Contact your doctor or health care provider right away if any of these apply to you.
Some medical conditions may interact with Zyrtec . Tell your doctor or pharmacist if you have any medical conditions, especially if any of the following apply to you:
if you are pregnant, plan to become pregnant, or are breast-feeding
if you are taking any prescription or nonprescription medicine, herbal preparation, or dietary supplement
if you have allergies to medicines, foods, or other substances
if you have kidney or liver problems, or are receiving dialysis

Do not drink alcohol or use medicines that may cause drowsiness (eg, sleep aids, muscle relaxers) while you are using Zyrtec ; it may add to their effects.

Ask a doctor or pharmacist if it is safe for you to take this medicine if you have any medical conditions.

Tell your doctor if you regularly use other medicines that make you sleepy (such as other cold or allergy medicine, narcotic pain medicine, sleeping pills, muscle relaxers, and medicine for seizures, depression, or anxiety). They can add to sleepiness caused by Zyrtec.

This list is not complete and other drugs may interact with Zyrtec. Tell your doctor about all medications you use. This includes prescription, over-the-counter, vitamin, and herbal products. Do not start a new medication without telling your doctor.

Important safety information: 

Do not use with any other antihistamines applied to the skin (such as diphenhydramine cream, ointment, spray) because increased side effects may occur.

If you are scheduled for allergy testing, ask your doctor if you should stop taking this medication for several days before testing. This drug may affect your allergy test results.

This document does not contain all possible interactions. Therefore, before using this product, tell your doctor or pharmacist of all the products you use. Keep a list of all your medications with you, and share the list with your doctor and health care provider.

All medicines may cause side effects, but many people have no, or minor, side effects. Check with your doctor if any of these most COMMON side effects persist or become bothersome when using Zyrtec:

Drowsiness; dry mouth; stomach pain (in children); tiredness; trouble sleeping (in children).

Seek medical attention right away if any of these SEVERE side effects occur when using Zyrtec:

Severe allergic reactions (rash; hives; itching; difficulty breathing; tightness in the chest; swelling of the mouth, face, lips, or tongue; unusual hoarseness); dark urine; fainting; fast or irregular heartbeat; mental or mood changes; persistent fatigue; seizures; severe dizziness; unusual bruising or bleeding; yellowing of eyes or skin.

This is not a complete list of all side effects that may occur. If you have questions about side effects, contact your health care provider. Call your doctor for medical advice about side effects.