Allegra and Zyrtec are both over-the-counter allergy medications that help prevent some of the same symptoms, such as running 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 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 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.
| Symptoms treated | Allegra | Zyrtec |
| runny nose | X | X |
| sneezing | X | X |
| itchy, watery eyes | X | X |
| itching of your nose or throat | X | X |
| hives* | X | X |
*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,
Allegra and Zyrtec are available OTC in many forms. The table below details the forms. For specific dosage information on either drug, read the product package carefully or talk to 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.
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 serious 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 | 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 | X | |
| excessive tiredness | X | |
| dry mouth | X | |
| stomach pain | X |
| 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 serious side effects that may indicate an allergic reaction, get emergency medical treatment right away.
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
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.
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.
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.