What are the possible side effects of Zyrtec?

October 14, 2025 •

3 min read

Though often considered a non-drowsy antihistamine, drowsiness occurs in a notable portion of users, with clinical studies indicating it affects up to 14% of patients taking cetirizine. Understanding what are the possible side effects of Zyrtec is important for anyone considering or currently taking this common over-the-counter allergy medication.

Quick Summary

An overview of Zyrtec's side effects, covering common reactions like drowsiness, dry mouth, and headache, as well as rarer complications such as severe allergic reactions and potential withdrawal symptoms after prolonged use. Drug interactions and precautions are also discussed.

Key Points

Common Side Effects: The most frequent side effects of Zyrtec include drowsiness, dry mouth, headache, and stomach issues like nausea or diarrhea.
Drowsiness is Possible: Despite being a second-generation antihistamine, Zyrtec can cause drowsiness, especially in higher doses or in children; taking it in the evening can minimize daytime effects.
Severe Withdrawal Itching: A rare but significant risk for long-term daily users is severe, widespread itching (pruritus) upon stopping the medication, with the FDA issuing a specific warning about this issue.
Risk of Serious Reactions: Though very rare, severe allergic reactions (anaphylaxis) can occur, and other rare side effects include mood changes, liver enzyme elevation, and cardiovascular effects.
Avoid Specific Interactions: It is crucial to avoid alcohol and other sedating medications (including opioids and certain cold medicines) while on Zyrtec to prevent excessive drowsiness and impairment.
Consult a Doctor for Long-Term Use: For long-term management of allergies or pre-existing health conditions like liver or kidney disease, consulting a healthcare provider is essential to discuss appropriate dosages and risks.

Common Side Effects of Zyrtec (Cetirizine)

Like all medications, Zyrtec (cetirizine) can cause a range of side effects, though many people tolerate the drug well with minimal issues. Common side effects include:

Drowsiness and Fatigue: While often called non-sedating, Zyrtec can cause drowsiness, which may be dose-related. It's advisable to know how you react before operating machinery. Taking Zyrtec in the evening can help manage daytime sleepiness.
Dry Mouth: This can be managed by staying hydrated or using sugar-free products.
Headache: Mild headaches can occur.
Gastrointestinal Issues: Some users experience stomach pain, nausea, vomiting, or diarrhea. Taking Zyrtec with food may help.
Sore Throat: This is a possible side effect.

Less Common and Rare Side Effects

Though not frequent, other side effects can occur:

Mood or Behavior Changes: Rarely, agitation, anxiety, hyperactivity, confusion, or more extreme reactions like hallucinations have been reported, especially with higher doses.
Liver Problems: Very rarely, temporary elevation of liver enzymes has been observed, returning to normal upon stopping the medication.
Cardiovascular Effects: Rare reports include palpitations and low blood pressure.
Urinary Retention: Difficulty urinating is rare, particularly in those with pre-existing conditions.
Vision Problems: Blurred vision has been reported rarely.

Long-Term Use and Withdrawal Effects

Long-term, daily use of cetirizine carries a rare risk of a specific withdrawal symptom.

Severe Pruritus (Itching): The FDA has issued a warning about severe, widespread itching after stopping long-term daily use of cetirizine. This is a withdrawal reaction, not a return of original allergy symptoms, and can be intense. Discuss long-term use with a healthcare professional.

Serious Allergic Reaction (Anaphylaxis)

Though rare, a severe allergic reaction to Zyrtec is possible and is a medical emergency.

Symptoms of anaphylaxis include hives, swelling of the face/throat, difficulty breathing, rapid heartbeat, or feeling faint. Seek emergency medical help if these symptoms occur.

Drug Interactions and Precautions

Zyrtec can interact with substances, increasing the risk of side effects, particularly drowsiness. Avoid the following while taking Zyrtec:

Alcohol: Significantly increases drowsiness.
Sedatives and Tranquilizers: Intensifies sedative effects.
Other Antihistamines: Increases side effect risk.
Narcotics and Opioids: Increases risk of severe drowsiness and dizziness.
Other Sedating Medications: Muscle relaxers and some antidepressants can increase drowsiness.
Pre-existing Conditions: Those with liver or kidney disease may need dose adjustments and should consult a doctor.

Comparing Zyrtec with Other Antihistamines

Here's a comparison of Zyrtec's side effects with Claritin and Benadryl:


Side Effect	Zyrtec (Cetirizine)	Claritin (Loratadine)	Benadryl (Diphenhydramine)
Drowsiness	Moderate, more likely than Claritin.	Minimal, very low-sedating.	High, often used as a sleep aid.
Onset of Action	Relatively quick.	Generally slower than Zyrtec.	Rapid, short-acting.
Duration	24 hours.	24 hours.	Short duration.
Common Side Effects	Headache, dry mouth, fatigue, nausea, diarrhea.	Headache, drowsiness, fatigue, dry mouth.	Drowsiness, dizziness, dry mouth, blurred vision.
Withdrawal Itching	Risk of severe itching after long-term daily use.	Not reported in the same way as Zyrtec.	Not associated with this specific withdrawal symptom.

Conclusion

Zyrtec is generally an effective and safe allergy medication. However, understanding what are the possible side effects of Zyrtec, including common issues like drowsiness and rare risks such as severe withdrawal itching and anaphylaxis, is crucial for safe use. Consult a healthcare professional before starting or stopping long-term use, especially with other health conditions or medications. Being aware of interactions and alternatives can help optimize treatment.

For more information on the risk of severe itching, see the FDA's drug safety communication.

Frequently Asked Questions

Yes, while Zyrtec is a second-generation antihistamine designed to be less sedating, it can still cause drowsiness in some individuals. Taking the dose at night can help reduce daytime sleepiness.

After long-term, daily use, some individuals may experience a rare but severe withdrawal symptom known as pruritus, or intense itching, which can be widespread and uncomfortable.

No, it is advised to avoid alcohol while taking Zyrtec. Combining them can significantly increase drowsiness and impair alertness.

The most common side effects include drowsiness, fatigue, dry mouth, headache, sore throat, and mild gastrointestinal issues like nausea or diarrhea.

Individuals with kidney or liver disease should consult a doctor before using Zyrtec, as a different dosage may be necessary.

Zyrtec-D is a combination medication containing cetirizine and the decongestant pseudoephedrine. It has additional side effects due to the decongestant, such as increased heart rate, elevated blood pressure, and restlessness or insomnia.

In rare cases, Zyrtec has been reported to cause mood changes such as agitation, anxiety, or confusion. If these occur, it is best to consult a healthcare professional.