Allegra (fexofenadine) is a non-drowsy antihistamine that blocks your body’s reaction to allergens. It treats seasonal allergy symptoms like sneezing, runny nose, itchy or watery eyes, and throat irritation. It’s also used to relieve chronic hives. The medication works fast, reaching peak histamine-blocking activity within 1 to 2 hours of taking it.
How Allegra Works in Your Body
When you’re exposed to pollen, pet dander, or another allergen, your immune system releases a chemical called histamine. Histamine latches onto receptors throughout your body, triggering the familiar cascade of allergy symptoms: swelling in your nasal passages, itching, sneezing, and watery eyes.
Allegra works by blocking those histamine receptors before the chemical can activate them. It’s selective for receptors outside the brain, which is why it doesn’t cause the drowsiness associated with older antihistamines like diphenhydramine (Benadryl). The liquid suspension is absorbed slightly faster than the tablet form, reaching peak blood levels in about 1 hour compared to 1.5 hours for tablets. Either way, maximum histamine suppression kicks in within 1 to 2 hours after you take a dose.
What Allegra Treats
Seasonal Allergies (Hay Fever)
Allegra’s primary use is relieving the nasal and eye symptoms triggered by seasonal allergens like tree pollen, grass pollen, and ragweed. It reduces sneezing, nasal congestion, runny nose, and the itchy, watery eyes that make allergy season miserable. Because it lasts up to 24 hours per dose, many people take it once daily throughout their allergy season for consistent relief.
Chronic Hives
Allegra is also effective for chronic idiopathic urticaria, the medical term for recurring hives without a clear cause. In a placebo-controlled trial, patients taking fexofenadine experienced significantly less itching and fewer hives compared to placebo. They also reported less interference with sleep and daily activities. Doses of 60 mg twice a day or higher were most effective, and side effects were mild and occurred at about the same rate as placebo.
Dosage by Age
For hay fever and hives, the standard adult dose is 180 mg once a day or 60 mg twice a day. Children aged 6 to 11 take 30 mg twice a day. Allegra is not recommended for children under 4, and dosing for children 4 to 6 should be determined by a doctor. These guidelines apply to both over-the-counter and prescription forms, according to the Mayo Clinic’s 2026 dosage information.
Why It Doesn’t Make You Drowsy
Older antihistamines like diphenhydramine and chlorpheniramine cross freely into the brain, where they block histamine receptors involved in wakefulness. That’s why they make you sleepy. Allegra was specifically designed to stay out of the central nervous system. It targets histamine receptors in your nose, throat, eyes, and skin without significantly crossing the blood-brain barrier. In clinical trials, the rate of drowsiness with fexofenadine was comparable to a sugar pill. This makes it a practical option if you need to drive, work, or stay alert during the day.
Food and Drink Interactions
One surprising quirk of Allegra is that fruit juice can dramatically reduce how much of the drug your body absorbs. Grapefruit, orange, and apple juice interfere with a transport protein in your gut that helps move fexofenadine into your bloodstream. A normal serving of one of these juices can cut absorption roughly in half, meaning you’d get significantly less symptom relief from the same dose.
The simplest fix is to take Allegra with water rather than juice. If you drink juice regularly, just space it at least a couple of hours away from your dose.
Antacids containing aluminum or magnesium also interfere with Allegra. Taking them together reduces the drug’s peak blood levels by about 43% and overall absorption by 41%. If you use antacids, take them at least 2 hours before or after your Allegra dose.
Side Effects
Allegra has one of the mildest side effect profiles among antihistamines. In clinical trials, the most commonly reported effects were headache, back pain, and nausea, but these occurred at rates similar to placebo. The chronic hives trial found that adverse events were mild across all dose groups, with no meaningful difference between patients taking fexofenadine and those taking a placebo.
Because it doesn’t penetrate the brain in significant amounts, Allegra avoids the cognitive impairment and dry mouth that are common with first-generation antihistamines. It also doesn’t carry the heart rhythm risks that pulled some older non-drowsy antihistamines (like terfenadine, its predecessor) off the market.
How to Get the Most Out of Allegra
For seasonal allergies, Allegra works best when taken consistently rather than as needed. Starting it a week or two before your allergy season begins can help keep symptoms from ramping up in the first place. Take it at the same time each day with a full glass of water, and avoid fruit juice and antacids around your dose. If you’re treating chronic hives, the twice-daily 60 mg dosing schedule tends to provide more even coverage than a single daily dose, though both approaches are effective.