Cetirizine: Uses, How It Works, and Safety Information

Overview

Cetirizine is a second-generation antihistamine commonly used to relieve symptoms of allergies. It is available over the counter in the United States under the brand name Zyrtec and as generic cetirizine. The medication was initially available by prescription beginning in 1995 and became available for over-the-counter purchase in 2007.

Cetirizine is classified as a second-generation antihistamine, which means it is less likely to cause drowsiness compared to older, first-generation antihistamines such as diphenhydramine. However, cetirizine does cause drowsiness in some people more frequently than some other second-generation antihistamines.

This page provides an overview of cetirizine, including what it is used for, how it works, common forms and strengths, who should use caution, and important safety considerations.

What Cetirizine Is Used For

Cetirizine is commonly used to manage symptoms associated with allergic conditions. These symptoms occur when the immune system reacts to substances such as pollen, dust mites, pet dander, or other allergens.

Common uses include relief of symptoms from:

Seasonal allergic rhinitis (hay fever)
Year-round (perennial) allergic rhinitis
Allergic conjunctivitis (itchy, watery eyes)
Hives (urticaria)
Itching from allergic skin reactions

Specific symptoms that cetirizine may help relieve:

Sneezing
Runny or stuffy nose
Itchy nose, throat, or eyes
Watery eyes
Itching from hives or other allergic skin reactions

Cetirizine treats the symptoms of allergies but does not address the underlying allergic condition or prevent allergic reactions from occurring. It works by blocking the effects of histamine, a chemical released during allergic reactions.

How Cetirizine Works

Cetirizine works by blocking histamine receptors in the body. Histamine is a chemical messenger released by the immune system when it encounters an allergen. When histamine binds to receptors on cells throughout the body, it triggers allergic symptoms such as itching, swelling, mucus production, and increased blood flow to affected areas.

By preventing histamine from binding to its receptors (specifically H1 receptors), cetirizine reduces or prevents these allergic symptoms from developing. This mechanism is the same for all antihistamines, though different antihistamines have varying properties in terms of how long they last, how well they cross into the brain, and how likely they are to cause drowsiness.

Cetirizine is considered a peripheral antihistamine, meaning it primarily acts outside the central nervous system. However, it does cross the blood-brain barrier to some degree, which is why it can cause drowsiness in some people, though less frequently than first-generation antihistamines.

The medication does not cure allergies or prevent future allergic reactions. It provides symptomatic relief while it is active in the body.

Available Forms and Strengths

Cetirizine is available in several forms to accommodate different preferences and age groups.

Common forms include:

Tablets (standard and orally disintegrating)
Capsules (liquid-filled)
Chewable tablets
Oral solution (liquid)
Syrup

Common strengths available over the counter:

5 mg tablets
10 mg tablets
1 mg per mL oral solution (typically used for children)

Some products combine cetirizine with a decongestant (such as pseudoephedrine) for additional relief of nasal congestion. These combination products have different indications and safety considerations compared to cetirizine alone.

For detailed information about dosing, see our page on cetirizine dosage.

Who Should Use Caution or Avoid Cetirizine

While cetirizine is generally considered safe for most people when used as directed, certain individuals should use caution or discuss use with a healthcare provider before taking it.

People who should use caution include those with:

Kidney disease or reduced kidney function (cetirizine is eliminated primarily through the kidneys)
Liver disease
History of urinary retention or difficulty urinating
Glaucoma
Enlarged prostate
Pregnancy or breastfeeding

People who may experience increased drowsiness:

Elderly individuals
Those taking other medications that cause drowsiness
People who consume alcohol
Those with sleep disorders

Activities requiring alertness:

People who drive, operate heavy machinery, or perform tasks requiring full alertness should be cautious when first taking cetirizine, as it can cause drowsiness in some individuals. It’s advisable to determine how the medication affects you before engaging in these activities.

Side Effects Overview

Most people tolerate cetirizine well, but side effects can occur. The most notable side effect is drowsiness, which occurs more frequently with cetirizine compared to some other second-generation antihistamines such as loratadine.

Common side effects may include:

Drowsiness or sedation
Fatigue or tiredness
Dry mouth
Headache
Dizziness

Less common side effects may include:

Nausea or stomach discomfort
Sore throat
Drowsiness severe enough to interfere with daily activities

Serious side effects are rare but may include:

Severe allergic reactions (rash, itching, swelling, difficulty breathing)
Rapid or irregular heartbeat
Difficulty urinating
Confusion or unusual behavior

For comprehensive information about side effects, their frequency, and when to seek medical attention, see our detailed page on cetirizine side effects.

Drug Interactions and Combination Products

Cetirizine has relatively few significant drug interactions compared to older antihistamines. However, some interactions are worth noting.

Potential interactions include:

Central nervous system depressants (alcohol, sedatives, sleeping medications, muscle relaxants, narcotic pain medications) may increase drowsiness
Other antihistamines may have additive effects
Some medications that affect kidney function may alter cetirizine levels in the body

Important considerations for combination products:

Many over-the-counter allergy and cold medications contain multiple active ingredients. Taking cetirizine along with other products that also contain antihistamines can result in excessive dosing. Always check the labels of all medications to avoid unintentional duplication of active ingredients.

People taking prescription medications should inform their healthcare provider before adding cetirizine to ensure there are no concerns with their specific medication regimen.

Onset and Duration of Action

Cetirizine is relatively fast-acting compared to some other second-generation antihistamines.

Timing characteristics:

Typically begins to work within 20 to 60 minutes after taking it
Peak effects occur at approximately 1 hour
Effects last approximately 24 hours
Taken once daily for ongoing allergy management

The quick onset of action makes cetirizine a common choice for people who need relatively fast relief of acute allergy symptoms. For detailed information about how long cetirizine takes to work and factors that influence its effectiveness, see our page on how long cetirizine takes to work.

Special Populations

Children

Cetirizine is available for children ages 2 and older in appropriate formulations and doses. Liquid forms are commonly used for younger children. Product labels provide specific guidance based on age and weight.

Elderly Individuals

Older adults may be more sensitive to the effects of cetirizine, particularly drowsiness and dizziness. Those with reduced kidney function may require dosage adjustments.

Pregnancy and Breastfeeding

Cetirizine is classified as Pregnancy Category B by the FDA, meaning animal studies have not shown risk, but there are no adequate studies in pregnant women. Many healthcare providers consider it a reasonable option for managing allergies during pregnancy, but medical guidance should be sought.

Cetirizine passes into breast milk in small amounts. While it is generally considered compatible with breastfeeding, discussing use with a healthcare provider is advisable.

People with Kidney Disease

Because cetirizine is eliminated primarily through the kidneys, people with reduced kidney function may need to take a lower dose or take the medication less frequently. Healthcare provider guidance is important for this population.

When to Seek Medical Care

While cetirizine is generally safe when used as directed, certain situations warrant medical attention.

Contact a healthcare provider if:

Allergy symptoms do not improve after several days of regular use
Symptoms worsen or new symptoms develop
Severe or persistent drowsiness interferes with daily activities
Unusual or concerning side effects occur
There is uncertainty about whether cetirizine is appropriate for a specific situation

Seek emergency medical care if:

Difficulty breathing or wheezing occurs
Severe swelling of the face, lips, tongue, or throat develops
Signs of a severe allergic reaction appear (hives, severe rash, rapid pulse)
Chest pain, rapid heartbeat, or fainting occurs
Confusion, hallucinations, or other unusual mental changes develop

These symptoms may indicate a serious condition requiring immediate medical attention and are not necessarily related to cetirizine use but may occur in the context of severe allergic reactions or other medical emergencies.

Sources

This information is based on data from the following authoritative sources:

U.S. Food and Drug Administration (FDA). Drug Approval Package: Cetirizine Hydrochloride.
MedlinePlus, U.S. National Library of Medicine. Cetirizine.
National Institutes of Health (NIH). Cetirizine—Clinical Pharmacology.
American Academy of Allergy, Asthma & Immunology. Antihistamine Use in Allergic Disease.
FDA Consumer Health Information. Allergy Relief for Your Child.
Clinical Pharmacology and Therapeutics. Second-Generation Antihistamines: Efficacy and Safety.