You have sneezing, runny nose, and itchy, watery eyes. This can only mean one thing: it’s 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, 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 available in prescription forms, as well, 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 allergic symptoms. Blocking it helps prevent symptoms of seasonal allergies or hay fever.

Symptoms treatedAllegraZyrtec
runny noseXX
itchy, watery eyesXX
itching of your nose or throatXX
*Not a typical symptom of seasonal allergies

Forms and dosage

Allegra and Zyrtec are available over-the-counter in many forms. The table below details the forms and the approved age ranges. For specific dosage information on either drug, read the product package carefully or talk to your doctor.

Oral tabletXX
Oral dissolving tabletXX
Oral gel capsule XX
Oral liquid syrup X
Oral liquid suspensionX
*Approved for use in people ages 12 years and older
**Approved for use in people ages 6 years and older

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, 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.

Side effects

Allegra and Zyrtec may cause mild side effects that may go away as your body gets used to the drug. Most of these do not call for medical attention. But tell your doctor if any side effects are especially bothersome or do not go away.

If you have serious side effects, call your doctor. If they’re severe, call 911 or go to the nearest emergency room.

The tables below list examples of side effects of Allegra and Zyrtec.

Common side effectsAllegra Zyrtec
pain in your arms, legs, or backX
menstrual crampsX
drowsiness X
excessive tiredness X
dry mouth X
stomach pain X
Serious side effectsAllegra Zyrtec
trouble breathing or swallowingXX
swelling of the face, throat, tongue, lips, eyes, hands, feet, ankles, or lower legsX


Drug interactions

If you’re taking other drugs, you should talk to 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 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. By taking your antacid at a different time from when you take Allegra, you can reduce this interaction.

Conditions of concern

Allegra and Zyrtec may also not be safe for people with certain health issues. For example, you should talk to 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 to your doctor before using Zyrtec.

Other warnings

You should not take Allegra with fruit juice. 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.

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. Some of these include:

  • Zyrtec can be used in people as young as 6 years, but Allegra should only be used in people who are 12 years or older.
  • You need to pay attention to what you drink with Allegra because fruit juices can affect how well it works.
  • Some of the mild and serious side effects that Allegra or Zyrtec can cause are different.

Your doctor 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.