Cetirizine vs Loratadine: Key Differences and When to Use Each

Overview

Cetirizine and loratadine are two of the most commonly used over-the-counter antihistamines in the United States for managing allergy symptoms. Both medications are classified as second-generation antihistamines, meaning they are less likely to cause drowsiness compared to older antihistamines. While they share similar uses and effectiveness, they have some differences in how quickly they work, how long they last, and their side effect profiles.

This page compares cetirizine and loratadine across several key areas, including how they work, what they’re used for, their side effects, and safety considerations.

What Are Cetirizine and Loratadine?

Cetirizine is a second-generation antihistamine available over the counter under the brand name Zyrtec and as generic cetirizine. It was approved by the FDA for over-the-counter use in 2007, though it was available by prescription for several years before that.

Loratadine is also a second-generation antihistamine available over the counter under the brand name Claritin and as generic loratadine. It became available without a prescription in the United States in 2002.

Both medications are available in various forms, including tablets, capsules, chewable tablets, and liquid suspensions. They are also available in combination products with decongestants.

How They Work Similarly

Both cetirizine and loratadine work by blocking histamine receptors in the body. Histamine is a chemical released by the immune system during allergic reactions and is responsible for many allergy symptoms such as sneezing, itching, runny nose, and watery eyes.

By preventing histamine from binding to its receptors, both medications help reduce or prevent allergic symptoms. Unlike first-generation antihistamines (such as diphenhydramine or chlorpheniramine), second-generation antihistamines like cetirizine and loratadine are designed to be less sedating because they do not cross into the brain as readily.

What They’re Used For

Both medications are commonly used to relieve symptoms of:

Seasonal allergic rhinitis (hay fever)
Year-round (perennial) allergic rhinitis
Itchy, watery eyes due to allergies
Sneezing and runny nose
Itchy nose or throat
Hives (urticaria)
Itching from allergic skin reactions

Neither medication treats the underlying cause of allergies—they only manage the symptoms. Both are intended for people ages 6 and older for most formulations, though children’s versions are available for younger ages.

For more detailed information, see our pages on cetirizine uses and loratadine uses.

Speed of Action: How Long Each Takes to Work

One of the key differences between these medications is how quickly they begin to work.

Cetirizine typically begins to provide relief within 20 to 60 minutes after taking it, with many people noticing effects within the first hour. Peak blood levels are reached approximately 1 hour after ingestion. The effects last approximately 24 hours, making it a once-daily medication.

Loratadine usually begins to work within 1 to 3 hours after taking it, which is slightly slower than cetirizine. Peak blood levels are reached at about 1 to 2 hours. Like cetirizine, loratadine’s effects last about 24 hours, so it is also taken once daily.

For people seeking faster relief of acute allergy symptoms, cetirizine’s quicker onset may be preferable. However, both medications are effective when taken regularly for ongoing allergy management.

For detailed information, see our pages on how long cetirizine takes to work and how long loratadine takes to work.

Comparing Side Effects

Both medications are generally well-tolerated, but they have slightly different side effect profiles.

Cetirizine Side Effects

Common side effects may include:

Drowsiness or sedation (more common than with loratadine)
Fatigue or tiredness
Dry mouth
Headache

Less common side effects may include:

Dizziness
Nausea
Stomach discomfort

While cetirizine is considered a non-sedating antihistamine, it is more likely to cause drowsiness compared to loratadine. Studies suggest that approximately 10 to 14% of people taking cetirizine experience some degree of drowsiness.

Loratadine Side Effects

Common side effects may include:

Headache
Fatigue
Dry mouth

Less common side effects may include:

Drowsiness (less common than with cetirizine)
Dizziness
Nervousness
Stomach discomfort

Loratadine is generally considered one of the least sedating antihistamines available. Studies indicate that drowsiness occurs in approximately 2 to 8% of people taking loratadine, which is comparable to placebo rates.

For comprehensive information, see our pages on cetirizine side effects and loratadine side effects.

Safety Considerations and Drug Interactions

Both medications have similar safety considerations, though there are some differences to be aware of.

Who Should Use Caution

People with the following conditions should discuss use with a healthcare provider:

Kidney disease (both medications are eliminated primarily through the kidneys)
Liver disease (particularly for cetirizine)
Pregnancy or breastfeeding (both are generally considered compatible, but medical guidance is recommended)
Elderly individuals (may be more sensitive to side effects)

For people with significant kidney impairment, dosage adjustments may be necessary for both medications, though cetirizine may require more significant adjustment.

Drug Interactions

Both medications have relatively few significant drug interactions compared to older antihistamines.

Potential interactions to be aware of:

Central nervous system depressants (alcohol, sedatives, sleeping pills) may increase drowsiness, particularly with cetirizine
Other medications that cause drowsiness may have additive effects
Some medications may increase blood levels of these antihistamines

Neither medication significantly interacts with grapefruit juice or most common medications, but it’s always advisable to inform healthcare providers about all medications being taken.

Driving and Operating Machinery

Because cetirizine is more likely to cause drowsiness, people should be cautious when first taking it and avoid driving or operating heavy machinery until they know how it affects them. Loratadine is less likely to impair cognitive function or cause drowsiness, but individual responses vary.

Dosage Considerations (Overview Only)

Both cetirizine and loratadine are typically taken once daily for ongoing allergy symptom management. The specific dosing for each medication varies based on age, individual health status, formulation type, and other factors.

Product labels provide detailed information about appropriate use for different age groups and circumstances. People with kidney or liver conditions may need different dosing approaches.

For comprehensive dosage information specific to each medication, see our detailed pages on cetirizine dosage and loratadine dosage.

How People Commonly Decide Between Them

In practice, the choice between cetirizine and loratadine often depends on individual factors and preferences.

People often choose cetirizine when:

They need faster relief of acute allergy symptoms
They have tried loratadine and found it less effective
Drowsiness is not a significant concern for them
They plan to take it in the evening

People often choose loratadine when:

They need to remain fully alert during the day
They have experienced drowsiness with cetirizine
They drive frequently or operate machinery
They prefer a medication with minimal sedation risk

Some people find that:

One medication works better for their specific symptoms than the other
Tolerance to drowsiness develops over time with cetirizine
Switching between the two medications can be helpful if one becomes less effective
Personal trial is the best way to determine which works better

Both medications are considered effective for allergy relief, and individual response can vary. What works well for one person may not be ideal for another.

When to Seek Medical Care

While both cetirizine and loratadine are safe for most people when used as directed, there are situations when medical attention is appropriate.

Contact a healthcare provider if:

Allergy symptoms do not improve after several days of use
Symptoms worsen or new symptoms develop
Severe drowsiness or dizziness occurs
Signs of an allergic reaction to the medication appear (rash, itching, swelling)
Allergy symptoms significantly interfere with daily activities despite medication use

Seek emergency medical care if:

Difficulty breathing or wheezing occurs
Severe swelling of the face, lips, tongue, or throat develops
Signs of anaphylaxis appear (rapid pulse, dizziness, severe rash)
Chest pain or rapid heartbeat occurs

It’s important to remember that antihistamines treat symptoms but do not address underlying allergic conditions. People with persistent or severe allergies may benefit from consultation with an allergist for comprehensive management.

Sources

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

U.S. Food and Drug Administration (FDA). Drug Approval Package: Cetirizine.
U.S. Food and Drug Administration (FDA). Drug Approval Package: Loratadine.
MedlinePlus, U.S. National Library of Medicine. Cetirizine.
MedlinePlus, U.S. National Library of Medicine. Loratadine.
National Institutes of Health (NIH). Antihistamines for Allergic Rhinitis Treatment.
American College of Allergy, Asthma & Immunology. Antihistamine Medications.
Clinical Pharmacology Review, Second-Generation Antihistamines.