Zyrtec Patient Tips

Medically reviewed by Carmen Pope, BPharm. Last updated on Aug 11, 2025.

1. How it works

• Zyrtec is used to temporarily relieve symptoms of hay fever or other respiratory allergies. It is a brand name for cetirizine.
• Zyrtec (cetirizine) works selectively on peripheral histamine-1 (H-1) receptors (these are histamine receptors that are located outside of the brain and spinal cord) to block the effects of histamine. Histamine is a chemical that is released by mast cells in response to an allergen, and it is responsible for many of the symptoms of an allergic reaction, such as swelling of the mucous membranes, sneezing, and itching. Zyrtec binds to histamine receptors and prevents histamine from having an effect on those receptors, which reduces the symptoms of an allergic reaction. Because it acts on peripheral histamine receptors, Zyrtec is much less likely to cause drowsiness compared with some older antihistamines.
• Zyrtec belongs to the drug class called antihistamines. Zyrtec may also be called an H1-antihistamine, a second-generation antihistamine, or a nonsedating antihistamine.

2. Upsides

• Used to temporarily relieve symptoms due to hay fever or other upper respiratory allergies such as a runny nose, sneezing, itchy or watery eyes, or itching of the nose or throat. May be used to relieve symptoms associated with an insect bite or hives.
• Less likely to cause sedation than older antihistamines such as promethazine.
• Can be taken once a day. The dosage for adults and children over the age of 6 is one 10 mg tablet once daily. 5 mg may be an appropriate dose for those less severe symptoms. Do not take more than 10 mg in 24 hours.
• May be given regularly, every day, when allergens are most prevalent (such as during spring or summer).
• Does not appear to interact with many drugs (theophylline slightly decreased the clearance of Zyrtec).
• A doctor's advice should be sought before using Zytrec in children younger than 6 years.
• No dosage adjustment is required in liver disease.
• Available over-the-counter.
• Zyrtec is available as a generic under the name of cetirizine.

3. Downsides

If you are between the ages of 18 and 60, take no other medication or have no other medical conditions, side effects you are more likely to experience include:

• A headache, sore throat, abdominal pain, fatigue, drowsiness, or coughing. Other side effects are uncommon. Stop using Zyrtec if you develop an allergy to it.
• Generally does not cause drowsiness, although more likely to do so at higher dosages. Caution should be exercised before driving or operating machinery until the full effects of Zyrtec are known. Alcohol, sedatives, and tranquilizers may enhance this effect and should be avoided.
• The dosage of Zyrtec should be reduced in kidney disease and caution should be exercised when Zyrtec is used in people with seizure disorders.
• Zyrtec, like all other antihistamines, may decrease the response to skin prick tests. Discontinue Zyrtec at least 72 hours before skin testing.
• Weigh up the risks versus benefits before using during pregnancy and breastfeeding.

Note: In general, seniors or children, people with certain medical conditions (such as liver or kidney problems, heart disease, diabetes, seizures) or people who take other medications are more at risk of developing a wider range of side effects. View complete list of side effects

4. Bottom Line

Zyrtec is used to temporarily relieve symptoms due to hay fever or other upper respiratory allergies such as a runny nose, sneezing, itchy or watery eyes, or itching of the nose or throat. It is a nonsedating antihistamine that may also be used to relieve symptoms associated with an insect bite or hives. Although drowsiness with Zyrtec is uncommon, it is more likely to cause drowsiness than loratadine, another nonsedating antihistamine.

5. Tips

• May be taken with or without food. Zyrtec is usually taken once a day. During the pollen season, your doctor may advise you to take it every day if you suffer from seasonal allergic rhinitis.
• Although Zyrtec is unlikely to make you drowsy, some people are susceptible to this effect, especially if they are taking dosages at the upper end of the recommended dosage range. Do not drive or operate machinery if Zyrtec makes you drowsy. Alcohol and other sedative-like drugs may cause additional reductions in alertness if used with Zyrtec.
• Seek urgent medical advice if you have hives and develop swelling of the face, throat, or tongue, dizziness, drooling, difficulty speaking, or shortness of breath.
• Zyrtec is not a substitute for epinephrine which is used for the treatment of severe allergies and anaphylaxis.
• Zyrtec is available as a tablet, chewable tablet, or a suspension for adults or children who have difficulty swallowing tablets.
• See your doctor if your mild allergy symptoms have not improved after three days of treatment with Zyrtec, or if your hives persist for more than six weeks despite taking Zyrtec.
• Discontinue Zyrtec once your allergy symptoms have resolved.
• Do not take Zyrtec during pregnancy or while breastfeeding unless on the advice of your doctor.

6. Response and effectiveness

• Peak concentrations are reached within one hour of administration of Zyrtec tablets or syrup. The onset of its effect occurs within 20 minutes in 50% of people and an hour in 95%.
• Effects persist for at least 24 hours following a single dose of Zyrtec. No tolerance has been found to Zyrtec's antihistaminic effect. Once discontinued, the skin recovers its normal reactivity to histamine within three days.
• Taking 10 mg of Zyrtec is more effective than taking 5 mg; taking 20 mg appears not to provide any additional effect.
• Food does not affect the overall absorption of Zyrtec; however, it may increase the time it takes for peak levels of Zyrtec to be reached in the blood.

7. Interactions

Medicines that interact with Zyrtec may either decrease its effect, affect how long it works, increase side effects, or have less of an effect when taken with Zyrtec. An interaction between two medications does not always mean that you must stop taking one of the medications; however, sometimes it does. Speak to your doctor about how drug interactions should be managed.

Common medications that may interact with Zyrtec include:

• anticonvulsants, such as fosphenytoin, lamotrigine, levetiracetam, phenytoin, or valproic acid
• antidepressants, such as clomipramine, escitalopram, or fluvoxamine
• antipsychotics, such as aripiprazole, chlorpromazine, or clozapine
• baclofen
• barbituates, such as butabarbital
• benzodiazepines, such as diazepam or temazepam
• benztropine
• bupropion
• buspirone
• cannabis and cannabinoids
• clonidine
• HIV medications such as darunavir, lopinavir, ritonavir, or saquinavir
• duloxetine
• ketamine
• lithium
• monoamine oxidase antidepressants, such as phenelzine, isocarboxazid
• mumps skin test antigen
• opioids, such as codeine, fentanyl, hydrocodone
• other antihistamines, such as azatadine, azelastine, or brompheniramine
• sleeping medications, such as zolpidem
• St John's wort
• topiramate
• voriconazole.

Alcohol may increase the risk of sedation with Zyrtec.

Note that this list is not all-inclusive and includes only common medications that may interact with Zyrtec. You should refer to the prescribing information for Zyrtec for a complete list of interactions.

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Frequently asked questions

• What cold medicine can you take with diabetes?
• Is it OK to take antihistamines every day?
• Zyrtec vs Claritin: Which is more effective for allergies?
• Does Zyrtec cause weight gain?
• Allegra vs Zyrtec: What's the difference?
• Which antihistamines make you drowsy?
• Can I take Allegra in the morning and Zyrtec in the evening?
• Can you take antihistamines when pregnant?
• I took Zyrtec for 1 year but have now stopped. How long does it stay in the body?

Further information

Remember, keep this and all other medicines out of the reach of children, never share your medicines with others, and use Zyrtec only for the indication prescribed.

Always consult your healthcare provider to ensure the information displayed on this page applies to your personal circumstances.

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