Allegra Vs. Zyrtec: How Do They Differ? - Healthline

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Allegra vs. Zyrtec: How Do They Compare?

Medically reviewed by Avi Varma, MD, MPH, AAHIVS, FAAFP — Written by University of Illinois — Updated on July 25, 2025

What they treat
Forms and dosage
Side effects
Warnings
Takeaway
Bottom line

Allegra and Zyrtec are both over-the-counter allergy medications that help prevent some of the same symptoms, such as a runny nose, itchy eyes, or sneezing. But Allegra and Zyrtec have different side effects.

Sneezing, runny nose, and itchy, watery eyes. This can only mean one thing: allergy season.

Seasonal allergies are typically caused by your body’s reaction to pollen, a substance produced by trees and other plants. When these allergies strike, your body combats them by creating the symptoms you so despise. When these occur, you may consider using an over-the-counter (OTC) medication to ease your symptoms.

Allegra and Zyrtec are two commonly used allergy drugs. Both are also available in prescription forms, but this article only covers the OTC versions. Here’s a side-by-side comparison to help you decide if one of them is right for you.

The symptoms they treat

The main active ingredient in Allegra is fexofenadine. The main active ingredient in Zyrtec is cetirizine. Both of these drugs are antihistamines.

Antihistamines work by blocking a substance called histamine in your body. Histamine is known for causing allergy symptoms. Blocking it helps prevent symptoms of seasonal allergies or hay fever. Both medications treat the following symptoms:

runny nose
sneezing
itchy, watery eyes
itching of your nose or throat
hives (not a typical symptom of seasonal allergies)

Both Allegra and Zyrtec are effective at treating allergy symptoms and take a similar amount of time to start working. However, some studies have found that Zyrtec’s beneficial effects last longer than those of Allegra.

Drug forms

Allegra and Zyrtec are available in many forms as OTCs. The table below details the forms. For specific dosage information on either drug, read the product package carefully or talk with your doctor or pharmacist.

Forms	Allegra	Zyrtec
Oral tablet	X	X
Oral dissolving tablet	X	X
Oral gel capsule	X	X
Oral liquid syrup	X
Oral liquid suspension	X

An oral chewable tablet is also available in a generic form of Zyrtec.

Depending on the form you choose, Allegra and Zyrtec may both be approved for use in people ages 2 years and older. You can find that information on the product label.

Remember to read the product label carefully. Many OTC cold and allergy drugs contain the same active ingredients, so taking them together with Allegra or Zyrtec could lead to an overdose of these ingredients.

Also, be sure to take Allegra or Zyrtec around the same time each day. This can ensure that you have just enough medication in your system to prevent allergies while also reducing the risk of side effects.

Common and severe side effects

Allegra and Zyrtec may cause mild side effects that tend to go away as your body gets used to the drug. Most of these don’t call for medical attention. But tell your doctor if any side effects are especially bothersome or don’t go away. Call your doctor or seek medical attention if you experience severe side effects.

The tables below list examples of side effects of Allegra and Zyrtec. Both Allegra and Zyrtec can cause similar side effects. The main difference is that Zyrtec is more likely to cause drowsiness than Allegra.

Common side effects

Common side effects	Allegra	Zyrtec
diarrhea	X	X
vomiting	X	X
headache	X
dizziness	X
pain in your arms, legs, or back	X
menstrual cramps	X
cough	X
drowsiness or fatigue	X
dry mouth	X
stomach pain	X

Serious side effects

Serious side effects	Allegra	Zyrtec
hives	X
rash	X
itching	X
trouble breathing or swallowing	X	X
swelling of the face, throat, tongue, lips, eyes, hands, feet, ankles, or lower legs	X
hoarseness	X

If you’ve taken either of these medications and are experiencing severe side effects that may indicate an allergic reaction, get emergency medical treatment right away.

Interactions and other warnings

Drug interactions

If you’re taking other drugs, you should talk with your doctor before using Allegra or Zyrtec. Either one can affect the way the other medications work in your body.

These interactions can increase or decrease the effect of the other medications, or of Allegra or Zyrtec. Interactions may also increase your risk of side effects from any drug you’re taking.

Zyrtec may interact with benzodiazepines or other central nervous system depressants, opioid pain relievers, or anti-asthma drugs such as theophylline.

Allegra may interact with drugs such as:

ketoconazole
erythromycin
rifampin
antacids

If you’re taking antacids such as Maalox or Mylanta, take Allegra a few hours before or after you take the antacid.

These antacids contain aluminum and magnesium, which can prevent your body from absorbing enough Allegra. This can make Allegra less effective. You can reduce this interaction by taking your antacid at a different time from when you take Allegra.

Conditions of concern

Allegra and Zyrtec may also not be safe for people with certain health issues. For example, you should talk with your doctor about how safe it is to use Allegra or Zyrtec if you have kidney disease.

If you have liver disease, you should also talk with your doctor before using Zyrtec.

Other warnings

Fruit juices such as grapefruit juice, orange juice, and apple juice can decrease the amount of Allegra that your body absorbs. This can make the drug less effective.

To avoid this interaction, wait at least 4 hours after drinking fruit juice before taking Allegra. Or you can wait 2 hours after taking Allegra to drink fruit juice. Make sure you take Allegra tablets with water, not juice.

You should also avoid taking Zyrtec and Allegra with alcohol. Combining the drugs with alcohol can cause excessive drowsiness.

Talk with your doctor

Allegra and Zyrtec treat the same symptoms and come in similar forms, but these drugs have a few key differences between them:

You need to pay attention to what you drink with Allegra because fruit juices can affect how well it works.
Zyrtec is more likely to cause drowsiness than Allegra.
The effects of Zyrtec may last a few hours longer than the effects of Allegra.

Your doctor or pharmacist can tell you more about Allegra and Zyrtec and which drug may be right for you. They can also give you advice on taking the drugs safely.

»MORE:Get an evaluation for seasonal allergies in as little as 15 minutes with Optum Now Online Care.

Optum Now is operated by RVO Health. By clicking on this link, we may receive a commission. Learn more.

The bottom line

Allegra and Zyrtec are common over-the-counter drugs used to treat allergy symptoms. Both drugs are safe and effective, but studies show Zyrtec’s effects may last longer than Allegra’s.

Zyrtec is more likely to cause drowsiness. Drinking fruit juices can make Allegra less effective.

How we reviewed this article:

SourcesHistoryHealthline has strict sourcing guidelines and relies on peer-reviewed studies, academic research institutions, and medical journals and associations. We only use quality, credible sources to ensure content accuracy and integrity. You can learn more about how we ensure our content is accurate and current by reading our editorial policy.

Allegra allergy - fexofenadine hydrochloride tablet, film coated. (2024).https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=81c1dcbb-28b3-4ad5-9f3d-9ccc16ddd173
Childrens allergy relief - cetirizine hcl tablet, chewable. (2017).https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=c67082d0-8524-42b0-bec8-af683363b999
Day JH, et al. (2005). Comparative efficacy of cetirizine and fexofenadine for seasonal allergic rhinitis, 5-12 hours postdose, in the environmental exposure unit.https://pubmed.ncbi.nlm.nih.gov/16270720/
Horak F, et al. (2001). Controlled comparison of the efficacy and safety of cetirizine 10 mg o.d. and fexofenadine 120 mg o.d. in reducing symptoms of seasonal allergic rhinitis.https://pubmed.ncbi.nlm.nih.gov/11385291/
Zyrtec allergy - cetirizine hydrochloride tablet, film coated. (2025).https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=b165db38-b302-4220-8627-77cb07bb078c

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Medically reviewed by Avi Varma, MD, MPH, AAHIVS, FAAFP — Written by University of Illinois — Updated on July 25, 2025

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The symptoms they treat

Drug forms

Common and severe side effects

Common side effects

Serious side effects

Interactions and other warnings

Drug interactions

Conditions of concern

Other warnings

Talk with your doctor

The bottom line

How we reviewed this article:

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