How Long Does Allegra Last? Plus 5 More Frequently Asked Questions About Allegra

If you experience seasonal allergies, you’re likely familiar with antihistamines. These oral medications are often a go-to choice when the pollen starts flying. They start working quickly and can help prevent allergy symptoms when taken every day. Allegra (fexofenadine) is a popular over-the-counter (OTC) antihistamine.

But just how long does Allegra take to work? And how long will it keep working? In this article, we will answer six frequently asked questions about Allegra. That way, you can decide if Allegra is the best allergy medication for you.

1. How long does Allegra take to work?

Typically, Allegra takes about 1 to 2 hours to start working for allergy symptoms such as sneezing and runny nose. Allegra also works within 2 hours for hives. This fast-acting quality can make it a good choice for people needing quick relief from allergy symptoms.

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2. How long does Allegra last?

Certain forms of Allegra can last for up to 24 hours for most people. But this can vary, depending on the dosage form you’re taking and whether you have kidney disease.

Allegra comes as 12- and 24-hour dosage forms. As the names suggest, 12-hour Allegra usually lasts for about 12 hours. And the 24-hour versions typically last for up to 24 hours.

The kidneys help clear Allegra from the body. If you have kidney disease, it may take longer for your body to clear the medication. You may need to take a lower daily dosage to avoid unwanted side effects. If you have a history of kidney problems, talk to your healthcare team before taking Allegra.

3. How does Allegra work?

As mentioned earlier, Allegra is an antihistamine. It works by blocking histamine in the body. Histamine is a natural substance in your body that can cause allergy symptoms such as sneezing, itchy or watery eyes, and runny nose. By blocking histamine, Allegra helps relieve these symptoms.

Good to know: Allegra is considered a nondrowsy antihistamine. It’s much less likely to cause drowsiness when compared to older antihistamines, such as Benadryl (diphenhydramine).

4. Can you take Allegra with fruit juice?

Fruit juices, such as grapefruit, apple, and orange juice, may decrease how much Allegra your body absorbs. This can lower its effectiveness. To avoid this possible interaction, you should separate Allegra from fruit juice by at least 4 hours.

Good to know: Green tea also affects how the body absorbs Allegra. You should separate the two by at least 4 hours as well.

5. What’s the difference between Allegra and Allegra-D?

Allegra and Allegra-D (fexofenadine / pseudoephedrine) sound similar, but they have notable differences. Both medications contain the antihistamine fexofenadine. But Allegra-D also contains pseudoephedrine, a nasal decongestant.

Pseudoephedrine can help relieve nasal congestion by tightening swollen blood vessels. So Allegra-D may be a better option if you’re experiencing a stuffy nose along with other allergy symptoms. But pseudoephedrine can raise your blood pressure and heart rate. So Allegra-D isn’t recommended if you have high blood pressure or other heart problems.

Both Allegra and Allegra-D are available without a prescription. But Allegra-D is kept behind the pharmacy counter. There are also limits on how much you can buy per day and per month. Allegra doesn’t have these restrictions.

6. What happens if you take 2 doses of Allegra in the same day?

If you take two of the 24-hour Allegra in the same day, don’t fret. You may experience mild side effects, such as drowsiness, headache, or dry mouth. Taking an extra dose by accident shouldn’t cause serious harm.

However, if you take an excessive amount of Allegra, more serious side effects can happen. Notably, Allegra overdoses can potentially cause an abnormal heart rhythm called long QT syndrome. In severe cases, long QT syndrome can be life-threatening. There’s also a risk of serious side effects if you combine antihistamines. These can include seizures, hallucinations, and even death.

Antihistamines are included in many OTC products, including sleep aids, menstrual cramp medications, and cold and flu products. Reading your medication labels carefully can help prevent an accidental antihistamine overdose. If you’re not sure whether a product contains an antihistamine, ask your pharmacist.

Good to know: Taking two 12-hour Allegra in the same day is OK. But the doses should be separated by about 12 hours to help prevent the side effects discussed above. For example, if you take the first dose at 7 AM, you shouldn’t take a second dose of 12-hour Allegra until 7 PM.

How to save on Allegra

There are ways to save on Allegra, which is available as both a brand-name and generic medication. By having a member of your healthcare team write a prescription for OTC Allegra, GoodRx can help you save over 80% off the average retail price. Allegra's price at certain pharmacies is as low as $7.66 with a free GoodRx discount.

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Written by:

Sarah Morin, RPh

Sarah Morin, RPh, has been a registered pharmacist for over 25 years. She started out as a hospital pharmacist, working at Rhode Island Hospital and then at the University of Connecticut Health Center.

Edited by:

Christina Aungst, PharmD

Christina Aungst, PharmD, is a pharmacy editor for GoodRx. She began writing for GoodRx Health in 2019, transitioning from freelance writer to editor in 2021.

Reviewed by:

Alyssa Billingsley, PharmD

Alyssa Billingsley, PharmD, is the director of pharmacy content for GoodRx. She has over a decade of experience as a pharmacist and has worked in clinical, academic, and administrative roles.

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