What is Cetirizine? How it Works, Dosage, and Interactions

Man holding tissues in front of face, about to sneeze.
  • Cetirizine is an active ingredient in many second-generation antihistamines like Zyrtec.

  • This medication works by suppressing the immune system’s reaction to allergens that produce histamine. Histamine causes most of the symptoms associated with allergies.

  • Medications that contain cetirizine don’t typically cause drowsiness, but some people have reported feeling sleepy.

  • Other potential side effects include headaches, dry mouth, and nausea. These side effects usually pass once the body becomes used to the medicine.

With more than 100 million people in the U.S. experiencing some type of allergy each year, it’s no surprise that the allergy medication ingredient cetirizine has become so popular.

Found in many over-the-counter (OTC) drugs, cetirizine is designed to treat and relieve the symptoms associated with an allergic reaction.

Cetirizine has become a common ingredient in antihistamines due to its affordability, how fast it works, and because it doesn’t typically lead to drowsiness.

What is Cetirizine?

Cetirizine Hydrochloride (HCI) — most commonly known as Zyrtec — is a second-generation FDA-approved antihistamine.

Second-generation means it causes less drowsiness and interacts with fewer medications than first-generation antihistamines.

Most people only need to take cetirizine once a day, while children under 12 typically take it twice daily. Cetirizine comes in the form of:

  • Capsules

  • Tablets

  • Gels

  • Syrup

  • Dissolvable tablets

What does cetirizine treat?

Cetirizine is formulated to treat the following allergic conditions:

  • Hay fever related to seasonal allergic rhinitis

  • Perennial allergic rhinitis

  • Conjunctivitis

  • Eczema

  • Hives as a result of urticaria

  • Allergic reactions to insect stings and bites

  • Certain food allergies

  • Chronic idiopathic urticaria

  • Allergic asthma

What are the potential side effects of cetirizine?

Although cetirizine is classified as a non-drowsy antihistamine, some people may experience some sleepiness as a result of taking this medication.

Other possible side effects of taking cetirizine include:

  • Headaches

  • Dry mouth

  • Dizziness

  • Diarrhea

  • Weakness

  • Sore throat

  • Nausea

If you experience any of these side effects and they become problematic, seek medical attention.

Key Point: What Happens During a Serious Allergic Reaction to Cetirizine?

Although very rare, some people may experience an allergic reaction to drugs that contain cetirizine. Get emergency medical help if you experience:

  • Wheezing, shortness of breath, or any other breathing problems
  • Tightness in your chest or throat
  • Swelling in your throat, lips, tongue, or mouth
  • A rash that includes swollen, itchy, or inflamed skin

How Effective is Cetirizine for Allergy Symptoms?

Since its FDA approval in 1995, cetirizine has undergone many studies to test its efficacy in treating allergy symptoms, particularly in comparison to other drugs.

Research shows that cetirizine is more effective than many other antihistamines at blocking the histamine reaction in the body.

When compared to another OTC antihistamine called loratadine, it was found that cetirizine worked faster and more effectively in treating seasonal allergies.

One study identified that children who took 5 mg of cetirizine for a period of four weeks during the high-pollen season experienced reduced allergy symptoms.

Other trials have found that a dose of 10 to 30 mg of cetirizine per day improved asthma and allergies in adults who took the medication for five to six weeks.

Woman blowing her nose.

Dosage and Duration of Cetirizine

The dose you take of this medication will depend on your age and how severe your allergy symptoms are.


Most children can take cetirizine. Depending on their age, they may need a prescription for this medication.

Here are the recommendations for cetirizine dosages based on a child’s age:


Dosage and form

Children aged 1 year and older

Can take cetirizine as a liquid medicine if it is prescribed by a doctor.

Children aged 2 years and older

Can take cetirizine liquid as an OTC drug or as prescribed by a doctor.

Children aged 6 years and older

Can take cetirizine tablets and in liquid form that can be bought from pharmacies.

Children aged 12 years and older

Can take cetirizine tablets, capsules, and liquid bought from pharmacies.


For individuals younger than 65, a dosage of 10 mg daily is recommended.

People in this age group should not exceed a 10 mg dose within a 24-hour period.

Your doctor may recommend splitting the 10 mg into two 5 mg doses twice daily if you have mild to moderate allergy symptoms.

Older adults

Older adults may need to take a lower dose of cetirizine, so it’s important to speak with a doctor about taking this medication if you are over 65.

Key Point: Is Cetirizine a Long-Term Drug?

Cetirizine is designed to be taken as a short-term treatment for allergy relief. However, your doctor may advise you to take this medication for an extended period.

If you have been taking an antihistamine drug that contains cetirizine for a long time and want to stop using it, speak to your doctor or pharmacist first.

How to Take Cetirizine

Antihistamines that contain cetirizine can be taken with or without food and should be taken with water or milk. It’s important not to chew or crush this medication.

Cetirizine typically takes about 20 minutes to an hour to work.

If you or your child is taking cetirizine in liquid form, it must be administered using a syringe or spoon to ensure the correct dosage. Ask your pharmacist for a proper medication spoon or syringe to ensure dosing accuracy.

What should I do if I’ve missed a dose?

If you forget to take your antihistamine medication, follow these guidelines:

  • If you have missed your usual dose of cetirizine, don’t take extra doses to make up for this.

  • Only take your missed dose if it’s not near the time for your next dose.

  • If you realize you have missed a dose and it is close to the time of your next dose, skip the missed one.

  • If your child takes cetirizine twice a day and misses a dose, you can give it to them within four hours of their usual dose. After this four-hour period, wait until the next dose.

Different forms of cetirizine on a table next to an allergy testing form.
Key Point: Can You Take Too Much Cetirizine?

This drug is considered quite safe, and taking more than your usual dose shouldn’t cause any harm.

Taking an extra dose by accident might trigger some of the common side effects listed above. Other overdose symptoms include feeling nervous or restless. You might also feel drowsy.

To avoid any adverse effects of taking too much cetirizine, visit your nearest emergency center.

Common Brand Names of Cetirizine

Cetrizine is an active ingredient in the following brand names of antihistamines:

  • Zyrtec

  • Zyrtec Allergy

  • Children’s Zyrtec Allergy

  • Children’s Zyrtec Hives Relief

  • PediaCare Children’s 24-Hour Allergy

  • Aller-Tec

  • Wal-Zyr

Who Shouldn’t Take Cetirizine?

Some health conditions make taking cetirizine dangerous. Talk to your doctor or pharmacist if you:

  • Have ever had an allergic reaction to cetirizine or other antihistamine ingredients

  • Have food allergies — especially if you’re allergic to peanuts or soya, as the coating on capsules can include these ingredients

  • Have kidney or liver disease

  • Have epilepsy or any other condition that causes fits and seizures

  • Have difficulty urinating for any reason

  • Are pregnant or breastfeeding

Key Point: Are You Due for an Allergy Test?

If your healthcare provider has asked that you take an allergy test, it’s important to note that taking cetirizine will affect the results.

To ensure accurate results, you should stop taking the medication a few days before your allergy test.

Understanding cetirizine-D

Cetirizine-D — or the brand name Zyrtec D — contains a decongestant called pseudoephedrine. This decongestant is a stimulant, which means it could negatively affect some health conditions.

If you have any of the following health problems, it’s not recommended that you take cetirizine-D:

  • Kidney disease, including kidney failure

  • High blood pressure (hypertension)

  • Cardiovascular disease

  • Thyroid disease

  • Diabetes

  • An enlarged prostate which could cause difficulty urinating

Drug Interactions with Cetirizine

Certain medications may increase your risk of developing the side effects associated with cetirizine.

If you are taking any drugs that lead to drowsiness, dry mouth, or urinary problems, it’s important to talk to your doctor, as this active ingredient can worsen these effects.

Also, some sleeping pills, tranquilizers, and first-generation antihistamines may interact with cetirizine. This means that they may prevent the ingredient from being absorbed properly in the body and may interfere with how it works.

Here are the names of some medications that may interact with cetirizine:


Active ingredient

Popular brand names

First-generation allergy medications

Diphenhydramine, hydroxyzine, and promethazine

Phenergan, Benadryl, and Vistaril

Tranquilizers (benzodiazepines)

Diazepam, lorazepam, alprazolam

Ativan, Valium, and Xanax

Sleeping medications

Eszopiclone, zaleplon, and zolpidem

Ambien, Lunesta, and Sonata

Other Interactions with Cetirizine

Food and beverages typically don’t interact with cetirizine, so you can eat and drink normally when taking this drug.

If you are taking a medication that contains cetirizine, you should avoid drinking alcohol. This is because cetirizine may cause some drowsiness as a side effect, and alcohol can worsen this symptom.

When to Talk to Your Doctor About Allergies

You should speak to your doctor or pharmacist if you experience allergic reactions regularly and if your symptoms affect your quality of life.

If your allergies are resulting in sinus infections, nasal congestion, or breathing difficulties, it’s also important to see a healthcare provider.

They can recommend or prescribe medication to manage and prevent allergies.

Where Can I Learn More About Cetirizine?

If you are experiencing allergies and would like to learn more about the drugs available to you, book an online consultation with LifeMD.

LifeMD can connect you with a board-certified physician or nurse practitioner to get allergy relief – all from the comfort of your home..

Head over to LifeMD website to book your telehealth consultation.

LifeMD makes it easy to stay on top of your health because talking to a doctor, filling your prescriptions, getting your labs done—and more—are all easy and cost-effective. Come discover a healthcare solution built around you and your life.

Connect with a doctor now!

This article is intended for informational purposes only and should not be considered medical advice. Consult a healthcare professional or call a doctor in the case of a medical emergency.

Feel better with LifeMD.

Your doctor is online and ready to see you.

Join LifeMD today and experience amazing healthcare, discounted labs and prescription medications... plus around-the-clock access to medical guidance.